A.O. Smith NW 37-670 User Manual

DURA-POWER MODELS NW 37- 670

COMMERCIAL ELECTRIC WATER BOILERS

• Installation • Operation • Service • Maintenance • Limited Warranty

CAUTION

STANDARD

TEXT PRINTED OR OUTLINED IN RED CONTINS INFORMA TION
RELATIVE TO YOUR SAFETY. PLEASE READ THOROUGHLY
BEFORE INSTALLING AND USING THE APPLIANCE.

FLOOD WARNING

IF THE BOILER SHOULD BECOME IMMERSED IN
WATER AT ANY TIME, THE BOILER SHOULD BE
EXAMINED BY A COMPETENT SERVICE PERSON
BEFORE IT IS RETURNED TO SERVICE.

PLACE THESE INSTRUCTIONS ADJACENT TO THE BOILER AND NOTIFY OWNER TO KEEP FOR

PRINTED IN U.S.A. 0004G 0900 P ART NO. 60047-002 REV.2

FUTURE REFERENCE.BE SURE THA T THE WARRANTY INFORMATION

HAS BEEN FILLED IN ON COMPLETION OF INSTALLATION.

1

A DIVISION OF A.O. SMITH CORPORATION

RENTON, WASHINGTON

www.hotwater.com

DIMENSIONAL DAT A

SIZES AND DATA 45KW THRU 720KW

Model Number Inlet* & Boiler

Prefix Gal.Cap. Std.KWInput D E F G** H J K S T U Outlet* Drain

NW 37 45K 32 30 12 42 12 1/2 - - 20 4 42 3 1
NW 37 60K 32 30 12 42 12 1/2 - - 20 4 42 3 1
NW 37 75K 32 30 12 42 12 1/2 - - 20 4 42 2 1
NW 37 90K 32 30 12 42 12 1/2 - - 20 4 42 3 1
NW 37 105K 32 30 12 42 12 1/2 - - 20 4 42 3 1
NW 37 120K 32 30 12 42 12 1/2 - - 20 4 42 3 1
NW 37 150K 32 30 12 42 12 1/2 - - 20 4 42 3 1
NW 37 180K 32 30 12 42 12 1/2 - - 20 4 42 3 1
NW 60 210K 32 30 12 57 12 1/2 - - 20 4 57 3 1
NW 60 240K 32 30 12 57 12 1/2 - - 20 4 57 3 1
NW 60 270K 32 30 12 57 12 1/2 - - 20 4 57 3 1
NW 60 300K 32 30 12 57 12 1/2 - - 20 4 57 3 1
NW 96 330K 40 38 16 691/2 17 1 1/2 17 24 5 78 4 1 1/4
NW 96 390K 40 38 16 69 1/2 17 1 1/2 17 24 5 78 4 1 1/4
NW 96 420K 40 38 16 69 1/2 17 1 1/2 17 24 5 78 4 1 1/4
NW 96 450K 40 38 16 69 1/2 17 1 1/2 17 24 5 78 4 1 1/4
NW 96 480K 40 38 16 69 1/2 17 1 1/2 17 24 5 78 4 1 1/4
NW 150 540K 54 44 19 69 1/2 20 2 20 27 5 1/2 69 1/2 5 1 1/2
NW 150 600K 54 44 19 69 1/2 20 2 20 27 5 1/2 69 1/2 5 1 1/2
NW 150 660K 54 44 19 69 1/2 20 2 20 27 5 1/2 69 1/2 5 1 1/2

NW 150 720K 54 44 19 69 1/2 20 2 20 27 5 1/2 691/2 5 1 1/2

* All fittings under 4” will be threaded type. All fittings 4” and larger will be flanged. 3” fittings extend 4” beyond jacket.
** Where overall height is a problem a larger diameter vessel with a reduced height may be furnished.
 Lifting lugs and channel skid base on 96 gallon and larger units.

2

SIZES AND DATA 780KW THRU 3300KW

Model Number Inlet* & Boiler

Prefix Gal.Cap. Std.KWInput D E F G** H J K S T Outlet* Drain

NW 220 780K 60 50 25 71 21 2 25 1/2 30 5 1/2 5 1 1/2
NW 220 840K 60 50 25 71 21 2 25 1/2 30 5 1/2 5 1 1/2
NW 220 900K 60 50 25 71 21 2 25 1/2 30 5 1/2 5 1 1/2
NW 220 960K 60 50 25 71 21 2 25 1/2 30 5 1/2 5 1 1/2
NW 220 1020K 60 50 25 71 21 2 25 1/2 30 5 1/2 5 1 1/2
NW 220 1080K 60 50 25 71 21 2 25 1/2 30 5 1/2 5 1 1/2
NW 220 1140K 60 50 25 71 21 2 25 1/2 30 5 1/2 5 1 1/2
NW 334 1200K 60 50 25 99 25 2 25 1/2 30 7 1/4 6 2
NW 334 1260K 60 50 25 99 25 2 25 1/2 30 7 1/4 6 2
NW 334 1380K 60 50 25 99 25 2 25 1/2 30 7 1/4 6 2
NW 334 1500K 60 50 25 99 25 2 25 1/2 30 7 1/4 6 2
NW 334 1620K 60 50 25 99 25 2 25 1/2 30 7 1/4 6 2
NW 334 1740K 60 50 25 99 25 2 25 1/2 30 7 1/4 6 2
NW 400 1800K 66 56 28 90 1/2 25 1/2 2 1/2 30 33 7 3/4 8 2
NW 400 1860K 66 56 28 90 1/2 25 1/2 2 1/2 30 33 7 3/4 8 2
NW 400 1980K 66 56 28 90 1/2 25 1/2 2 1/2 30 33 7 3/4 8 2
NW 400 2100K 66 56 28 90 1/2 25 1/2 2 1/2 30 33 7 3/4 8 2
NW 500 2200K 72 62 31 90 1/2 26 1/2 2 1/2 34 36 7 3/4 8 2
NW 500 2340K 72 62 31 90 1/2 26 1/2 2 1/2 34 36 7 3/4 8 2

NW 500 2460K 72 62 31 90 1/2 26 1/2 2 1/2 34 36 7 3/4 8 2
NW 500 2580K 72 62 31 90 1/2 26 1/2 2 1/2 34 36 7 3/4 8 2

NW 670 2700K 78 68 34 96 1/2 30 1/2 2 1/2 38 39 7 3/4 8 2
NW 670 2820K 78 68 34 96 1/2 30 1/2 2 1/2 38 39 7 3/4 8 2
NW 670 2940K 78 68 34 96 1/2 30 1/2 2 1/2 38 39 7 3/4 8 2
NW 670 3060K 78 68 34 96 1/2 30 1/2 2 1/2 38 39 7 3/4 8 2
NW 670 3180K 78 68 34 96 1/2 30 1/2 2 1/2 38 39 7 3/4 8 2

NW 670 3300K 78 68 34 96 1/2 30 1/2 2 1/2 38 39 7 3/4 8 2
NOTE: For boilers 3400KW to 6000KW, consult factory.
* All fittings under 4” will be threaded type. All fittings 4” and larger will be flanged.
** Where overall height is a problem a larger diameter vessel with a reduced height may be furnished.

3

ELECTRICAL/RECOVERY DATA

Model Number

Prefix Cap. Input 100°F Rise Elements Steps and KW of Steps 208v 240V 480V 575V

NW 37 45K 153,585 180 3 1 1@45 128 108 55 45
NW 37 60K 204,720 240 4 1 1@60 171 144 73 60
NW 37 75K 255,975 300 5 1 1@75 213 180 90 75
NW 37 90K 307,170 369 6 3 3@30 250 217 108 90
NW 37 105K 358,365 430 7 4 3@30+1@15 292 253 126 105
NW 37 120K 409,560 492 8 4 4@30 334 289 144 121
NW 37 150K 511,950 615 10 5 5@30 417 361 180 151
NW 37 180K 614,340 738 12 5 4@30+1@60 500 433 216 181
NW 60 210K 716,730 861 14 5 3@30+2@60 584 505 252 211
NW 60 240K 819,120 984 16 5 2@30+3@60 668 577 288 241
NW 60 270K 921,510 1107 18 5 1@30+4@60 751 650 324 271
NW 60 300K 1,023,900 1230 20 5 5@60 834 722 360 301
NW 96 330K 1,126,290 1353 22 6 5@60+1@30 917 794 396 331
NW 96 360K 1,228,680 1476 24 6 6@60 1001 866 432 362
NW 96 390K 1,331,070 1599 26 7 6@60+1@30 1084 938 468 392
NW 96 420K 1,433,460 1722 28 7 7@60 1168 1010 504 422
NW 96 450K 1,535,850 1845 30 8 7@60+1@30 1251 1083 540 452
NW 96 480K 1,638,240 1968 32 8 8@60 1334 1155 576 487
NW 150 540K 1,843,020 2214 36 9 9@60 1501 1299 648 542
NW 150 600K 2,047,800 2460 40 10 10@60 1668 1443 720 602
NW 150 660K 2,252,580 2706 44 10 8@60+2@90 792 663
NW 150 720K 2,457,360 2952 48 8 8@90 864 723
NW 220 780K 2,662,140 3198 52 9 8@90+1@60 936 783
MW 220 840K 2,866,920 3444 56 10 9@90+1@30 1008 843
NW 220 900K 3,071,700 3690 60 10 10@90 1080 904
NW 220 960K 3,276,480 3936 64 10 8@90+2@120 1152 964
NW 220 1020K 3,481,260 4182 68 10 6@90+4@120 1224 1024
NW 220 1080K 3,636,040 4428 72 10 4@90+6@120 1296 1084
NW 220 1140k 3,890,820 4674 76 10 2@90+8@120 1368 1145
NW 334 1200K 4,095,600 4920 80 10 10@120 1440 1205
NW 334 1260K 4,300,380 5166 84 10 8@120+2@150 1512 1265
NW 334 1380K 4,709,940 5658 92 10 4@120+6@150 1656 1386
NW 334 1500K 5,119,500 6150 100 10 10@150 1800 1506
NW 334 1620K 5,529,060 6642 108 15 6@90+9@120 1944 1627
NW 334 1740K 5,938,630 7134 116 15 2@90+13@120 2068 1747
NW 400 1800K 6,143,400 7380 120 15 15@120 2160 1807
NW 400 1860K 6,348,180 7626 124 15 13@120+2@150 2232 1868
NW 400 1980K 6,757,740 8118 132 15 9@120+6@150 2376 1988
NW 400 2100K 7,167,300 8610 140 15 5@120+10@150 2520 2109
NW 500 2200K 7,576,860 9102 148 15 1@120+14@150 2664 2229
NW 500 2340K 7,986,420 9594 156 20 18@120+2@90 2808 2350
NW 500 2460K 8,395,980 10080 164 20 18@120+2@150 2952 2470
NW 500 2580K 8,805,540 10578 172 20 14@120+6@150 3096 2590
NW 670 2700K 9,315,100 11070 180 20 10@120+10@150 3240 2711
NW 670 2820K 9,624,660 11562 188 20 6@120+14@150 3384 2832
NW 670 2940K 10,034,220 12054 196 20 2@120+18@150 3528 2952

Gal. Std. KW BTU Output Gal./Hr. Number of Number of Standard Number Amperage 3 Phase

Not Recommended

Not Recommended

WATER BOILER SPECIFICATIONS

NOTE: For boilers 3000KW to 6000KW consult factory.

MODEL AND RA TING PLATE

4

FOREWORD

APPROVALS

These designs comply with requirements of Underwriters Laboratories
and bear the U.L. label on the cabinet.

All models are built to the standards of Section lV of the American
Society of Mechanical Engineers. Boiler and Pressure Code,
inspected and identified by this symbol.

The ASME plate is located on the tank above the cleanout opening.
When specified, the National Board of Boiler and Pressure Vessel
Inspectors listing will be furnished and identified by an NB number on
the ASME plate.

FEATURES

INST ALLATION CODE REQUIREMENTS

In addition to these instructions, the equipment shall be installed in
accordance with those installation regulations in force in the local
area where the installation is to be made. These shall be carefully
followed in all cases. Authorities having jurisdiction should be
consulted before installations are made.

In absence of local codes the installation must comply with the latest
edition of the National Electrical Code, NFPA 70. Copies of this
document are available from the National Fire Protection Association,
1 Batterymarch Park, Quincy, MA 02269.

GROUNDING

Grounding and electrical wiring connected to the boiler must conform
to the latest edition of the National Electric Code, NFPA 70.

Figure 1, below, is an illustration of a typical model NW/Commercial
Electric Hot Water Boiler with the features called out.

FIGURE 1

5

IMPORTANT

LOCATING THE BOILER

IT IS RECOMMENDED THA T A QUALIFIED SERVICE TECHNICIAN
PERFORM THE INITIAL FIRING OF THE BOILER. AT THIS TIME
THE USER SHOULD NOT HESITATE TO ASK THE TECHNICIAN
ANY QUESTIONS WHICH THEY MAY HAVE IN REGARD TO THE
OPERATION AND MAINTENANCE OF THE BOILER.

BEFORE FILLING THE SYSTEM FOR OPERATION the hot water
system should be internally cleaned and flushed to remove any
contaminants which may have accumulated during installation. See
section of this manual titled SYSTEM CLEANING.

RELIEF V ALVE

An ASME rated pressure relief valve is furnished with the boiler. A
fitting for the relief valve is provided in the top of the boiler. A drain
line from the relief valve should terminate near a suitable drain. Do
not thread, plug, or cap the end of the drain line.

The pressure setting of the relief valve should not exceed the pressure
capacity of any component in the system including the boiler.

HIGH TEMPERA TURE DEVICES

Automatic Device

The boiler control circuit contains a high temperature cutoff switch.
This device shuts off the heating elements if excessive water
temperatures are reached. The high temperature cutoff has an
adjustable range of 100° to 240°F and automatically resets on a drop
of temperature.

Manual Device

A manual reset high limit will be in the control circuit in addition to the
automatic device previously described. The control has an adjustable
range of 110° to 290°F and must be manually reset after a drop of
temperature.

Reset button is located under the right side panel of the boiler.
Disconnect the power before removing the panel to push the button.

INSTALLATION

REQUIRED ABILITY

INSTALLATION OR SERVICE OF THIS BOILER REQUIRES ABILITY
EQUIVALENT TO THAT OF A LICENSED TRADESMAN IN THE
FIELD INVOLVED. PLUMBING AND ELECTRICAL WORK ARE
REQUIRED.

For the best installation, the boiler should be located:

1. On a level surface.

• Shim the channel type skid base as necessary if leveling
is required.

2. Near a floor drain.

• The boiler should be located in an area where leakage of
the tank or connections will not result in damage to the
area adjacent to the boiler or to lower floors of the
structure. When such locations cannot be avoided, a
suitable drain pan should be installed under the boiler.

The pan should be at least two inches deep, have a
minimum length and width of at least two inches greater
than the dimensions of the boiler and should be piped to
an adequate drain.

• The discharge opening of the relief valve should always
be piped to an open drain.

3. Suggested clearances from adjacent surfaces are found on a label
attached to the control compartment door.

• UL minimum clearances:

- 24” all sides

- 12” top

• Allow clearance for hinged control compartment doors.

• Elements can be changed with 24” clearance.

4. The boiler may be installed in a confined space if adequate
ventilation is provided.

ELECTRICAL

General

Check the boiler model and rating plate information against the
characteristics of the branch circuit electrical supply. Do not connect
the boiler to an improper source of electricity.

Vo ltage applied to the boiler should not vary more than + 5% to -10%
of the model and rating plate marking for satisfactory operation.

Do not energize the branch circuit for any reason before the boiler is
filled with water. Doing so may cause the heating elements to burn
out. Such damage is not covered under the terms of the warranty.

The branch circuit is connected to the block through an opening
provided on top of the boiler.

GENERAL

Do not test electrical system before boiler is filled with water, follow
START UP procedure in this manual.

The principal components of the boiler are identified in Figure 1. The
model and rating plate, see illustration on page 4, provides certain
useful information required at installation. Both of these references
should be used to identify the boiler and its components.

Water boilers are usually placed in series with the heating system on
the outlet side of the circulating pump. The boiler piping should include
inlet and outlet water valves to permit maintenance and service work
to be performed without disturbing the rest of the system.

Detailed system installation drawings are normally provided by the
equipment purchaser or system designer.

The boiler should be connected to a separate, grounded, branch circuit
with overcurrent protection and disconnect switch. These are part of
the electrical supply system not components of the boiler, as such
they are obtained locally . The boiler should be grounded in accordance
with national and local codes.

Branch Circuit

The branch circuit wire size should be established through reference
to the National Electrical Code or other locally approved source in
conjunction with boiler amperage rating. Branch circuit wiring which
connects to the boiler terminal block should be temperature rated at
75°C. For convenience, portions of the wire size tables from the
Code are reproduced here. It is suggested the electrician size the
branch circuit at 125 percent of the boiler rating and further increase
wire size as necessary to compensate for voltage drop in long runs.
Branch circuit voltage drop should not exceed 3% at the boiler.

6

Calculating Amperage/Overcurrent Protection

The boiler is factory wired for connection to three wire single-phase
or three and four wire three-phase branch circuits. In addition, a
ground conductor may be required.

A diagram of the wiring is furnished with the boiler for the electrician’s
use. An amperage table is on page 4 of this manual. The boiler
model and rating plate provides full load amperage data.

The rating of the overcurrent protection should be computed on the
basis of 125 percent of the total connected load amperage. Where
the standard ratings and settings do not correspond with this
computation, the next higher standard rating or setting should be
selected.

Boiler Circuits

The boiler’s electrical components are pictured and identified on page

5. The model and rating plate illustration on page 4 identifies the
electrical characteristics. Basically, there are two electrical circuits:

• The control circuit, where the temperature control directly or
indirectly operates the contactor coils.

• The power circuit, which is operated by the control circuit, carries
the electrical load of the heating elements.

The following describes the circuits and includes typical wiring
diagrams. All circuits are designed for 60 or 50 Hertz alternating
current.

Refer to ELECTRICAL CONFIGURATION TABLE, below, and wiring
diagram provided with your boiler before completing connections to
electrical supply.

NOTE: Wiring diagrams in this manual are typical examples. The
specific wiring diagram for your boiler is the one supplied with the
boiler.

Control Circuit

All control circuits are operated on single-phase 120V . A transformer
is used in the control circuit.

Control circuit wiring is 14 Awg, THHN or THWN type, rated 600 volts,
105°C.

Portion of Table 310-16

Allowable Ampacities of Insulated

Copper Conductors

Not more than three conductors in

raceway or cable or direct burial

(based on ambient temperature of

30°C, 86°F.)

Temperature Rating of Temperature Rating of

Conductor. See Table Conductor. See Table

Size 310-13 in Code Size 310-13 in Code
AWG 75°c AWG 75°C
MCM (167°F) MCM (167°F)

TYPES TYPES

RH, RHW, RUH RH, RHW, RUH

(14-2), (12-2),

THW, THWN, THW, THWN,

XHHW, USE XHHW, USE

18 - - - - - 12 15
16 - - - - - 10 25
14 15 8 40
12 20 6 50
10 30 4 65

845 3 75
665 2 90
4 85 1 100
3 100 1/0 120
2 115 2/0 135

1 130 3/0 155
1/0 150 4/0 180
2/0 175 250 205
3/0 200 300 230
4/0 230 350 250

250 255 400 270
300 285 500 310
350 310 600 340
400 335 700 375
500 380 750 385
600 420 800 395
700 460 900 425
750 475 1000 445
800 490 1250 485

900 520 1500 520
1000 545 1750 545
1250 590 2000 560
1500 625
1750 650
2000 665

Portion of T able 310-16

Allowable Ampacities of

Insulated Aluminum and Copper-

Clad AluminumConductors

Not more than three conductors

in raceway or cable or direct

burial (based on ambient

temperature of 30°C, 86°F.)

These capacities relate only to conductors
described in Table 310-13 in Code.

For ambient temperatures over 30°C, see
Correction Factors, Note 13 in Code

Power Circuit

The boiler is equipped with one of the power circuit configurations
shown in the table.

Seperate instructional literature is provided with the boiler for the
modulating solid state step control.

Power circuit wiring is type THHN, rated 600 volts, 105°C, sized as
necessary.

7

ELECTRICAL CONFIGURA TION TABLE

Boiler Type Voltage Between Control Elements

Nameplate of Boiler Terminal Circuit Quantity Element

Markings Service Lugs Voltage Per Operating

Voltage Phase (1 Phase) Contractor Voltage

1

208

3 Delta

(With 120 1 208

Neutral)

1 120 1 240

240

3 Delta 120 1 240

L1 L2 N G

208

120

L1 L2 L3 N G

208

L1 L2 G

240

L1 L2 L3 G

240

208

240

208

120

240

120 1 208

480 3 Wye* 120 1 or 2 277

480 3 Delta 120 1or 2 480

* Neutral lug not necessary and not furnished due to three wire wye connection. This means only three wires (no neutral)
brought to boiler due to method of element connection. Elements operate at 277 volts.
Voltage from a conductor to ground (electrical raceway and water pipes) is not measured.
No ground lug furnished. If required installer can provide locally.

L1 L2 L3 G

480

L1 L2 L3 G

480

480

480

480

480

TYPICAL WIRING DIAGRAMS

The following wiring diagrams are included in this manual to show
typical arrangements of electrical components in the control and
power circuits by voltage and phase charactreristics. They are
to be used as a reference by the installer or servicer in performing
their work. A diagram of the boiler wiring is furnished with the
boiler.

WIRING DIAGRAM 208V OR 240V THREE-PHASE (DEL TA) WITH STEP CONTROL

8

WIRING DIAGRAM 480V THREE-PHASE (WYE)

SYSTEM CLEANING

The hot water system should be internally cleaned and flushed to
remove contaminants which may have accumulated during installation.
System cleaning provides chemical stability necessary for component
life and system performance.

Failure to clean the system may cause:

1. Poor heating due to formation of gas.

• Residual pipe dope, thread cutting oil, solder flux, dirt and
other foreign materials breakdown to form gas. This is
indicated by a continuing need for purging even through
the system is “closed”.

2. Pump seal leakage.

• Acidic water (low pH) and contamination such as soil and
sand result in premature or recurring pump seal failures.

3. Automatic air valve leakage.

• Contaminants cause sticky sealing surfaces and result in
leakage.

4. Relief valve operation.

• Gas formation increases system pressure and relief valve
spillage.

5. Water leaks at joints and fittings.

• Corrosion and eventual failure of connections occur when
system pH is low.

6. Noisy operation.

• Heat transfer surfaces can be fouled with dirty, oily water.
This plus gas lead to noisy water circulation.

OPERATION

GENERAL

Never operate the heating elements without being certain the boiler
is filled with water and a pressure relief valve is installed in the relief
valve opening provided.

An electronic type low water cutoff is provided on all boilers as standard
equipment. The water probe is installed near the top of the tank to
monitor the presence of water. The control circuit is opened if the
water level is below this point.

The pilot switch on the cabinet front permits the boiler to be turned on
and off without having to operate the electrical disconnect switch.
Additional switches may be provided for manually operating contactor
coils.

WARNING

Full power is present whenever the cabinet door is opened even with
the pilot switch(es) turned off. Never operate the boiler with cabinet
doors open or panels removed.

FILLING

Refer to SYSTEM CLEANING section for preparing the system prior
to final filling and operation.

Hard Water: in areas which have hard water it may be desirable to fill
the system with soft water and/or provide water treatment as
recommended by a consultant familiar with local conditions. In this
way harmful water scale build-up on the heating elements is minimized.

WARNING

Be sure to turn off power when working on or near the electrical system
of the boiler. Never touch electrical components with wet hands or
when standing in water. When replacing fuses always use the correct
size for the circuit.

1. Close the boiler drain valve and system valves as necessary.

2. Open a vent in the highest point of the system to allow the air to
escape.

3. Fully open the make-up water inlet valve. Fill the boiler and piping.

9

4. Close the vent as water starts to flow from the opening. Place the
make-up water valve in the desired position. The boiler is now
ready for ST ART U P and TEMPERATURE REGULATION if being
placed in operation for the first time.

Tank flushing and circulating pump lubrication should be performed
in accordance with the above schedule. Tank sediment removal and
element lime scale removal must be performed when needed as
determined by period inspections. Following are the instructions for
performing recommended maintenance.

ST ART UP

The following checks should be made by the installer when the boiler
is placed into operation for the first time:

1. Check all factory and field made water and electrical connections
for tightness.

• Repair water leaks and tighten electrical connections

as necessary.

2. Turn on the electrical disconnect switch and pilot switch(es)
mounted on the boiler cabinet.

3. Observe the operation of the boiler during the first heating cycle.

• T emperature control and contactor operation should be

checked by allowing the boiler to come up to temperature
and shutoff automatically.

TEMPERA TURE REGULA TION

Always turn off the electricity at the electrical disconnect switch when
making a temperature control adjustment.

It is suggested the temperature adjustment be turned to the lowest
setting which satisfies the hot water requirements of the system.

• Additional instructional literature is provided with the boiler for
adjusting this control.

Always close and lock the cabinet door after making a temperature
adjustment. Turn on electricity.

DRAINING

FLUSHING

1. Turn off the electrical disconnect switch.

2. Open the boiler drain valve. Allow water to flow to an open drain
until it runs clean. Do not come in contact with the water being
drained as it may be very hot.

3. Close the drain valve when finished flushing.

4. Turn on the electrical disconnect switch.

SEDIMENT REMOV AL

Water borne impurities consist of fine particles of soil and sand which
settle out and form a layer of sediment on the bottom of the tank. In
time, if not removed, the level of sediment might reach the heating
elements.

For convenience, sediment removal and element lime scale removal
should be performed at the same time as follows:

W ATER AND LIME SCALE REMOVAL

Water and lime scale accumulations on the heating elements is a
normal condition, common to all immersion type elements. Factors
which affect the amount of this formation are:

1. Amount of make-up water used. As the volume of make-up water
heated increases, more scale results.

The boiler must be drained if it is to be shut down and exposed to
freezing temperatures. Maintenance and service procedures may
also require draining the boiler.

1. Turn off the electrical disconnect switch.

2. Close the make-up water valve and system valves as necessary.

3. Open a nearby outlet to vent the parts of the system being drained.

4. Open the boiler drain valve.

5. If the boiler is being drained for an extended shutdown, it is
suggested the drain valve be left open during this period.

• Follow FILLING instructions to restore boiler to service.

MAINTENANCE

Boiler maintenance includes periodic tank flushing and cleaning, and
removal of lime scale from the heating elements. Circulating pumps
should be oiled.

MAINTENANCE SCHEDULE

Component Operation Interval Required

Flushing Monthly

Tank Sediment As Needed

Removal
Lime Scale As Needed UN•LIME

Elements Removal Delimer and

element

gaskets.
Circulating Oiling Per pump makers
Pump(s) instructions

®

2. Water temperature. As the temperature of the water is increased,
more scale is deposited on the elements.

3. Characteristics of water supply. Regardless of water treatment,
the elements should be examined regularly .

Water scale accumulations may cause noises to occur during
operation.

It is recommended that a lower heating element be removed
periodically for examination. If it is scaled, all of the elements should
be removed and cleaned. If the tank bottom has an accumulation of
sediment, it should be cleaned.

Lime scale should be removed from the elements by dissolving the
accumulation in UN•LIME
delimer, available through your dealer or distributor . Do not use muratic
or hydrochloric acid base deliming solutions to remove lime scale
from the elements. Do not pour delimer into tank.

All models:

1. Turn off electrical disconnect switch.

2. Drain the boiler following DRAINING instructions.

3. Remove the cabinet panel which covers the heating elements.

• Remove insulation as necessary to reach the element

area.

4. Remove the bolts from each element and remove the elements
from the opening.

• Disconnect element wiring as necessary.

10

®

delimer. UN•LIME is a non-muriatic

• Use a twisting, pulling action to remove elements scaled
beyond the size of the tank opening.

• Brush loose scale from elements.

• Silicates, sulfates and aluminates must be removed by

scraping or other mechanical means. Lime scale
dissolvents will not remove these types of scale which
are occasionally encountered.

5. Lime scale removal:

• Place limed ends of heating elements into UN•LIME
delimer and allow scale to dissolve. Do not permit
delimer or water to contact heating element electrical
terminals.

6. Flush cleaned ends of elements with water when deliming or
cleaning is completed.

7. Remove sediment and scale from the tank bottom through the
tank cleanout.

• The make-up water valve and boiler drain valve may be

opened to flush during the cleanout process.

8. Clean remaining gasket material from tank and element flanges.
Do not reuse original element gasket. The element gasket is Part
No. 5109.

9. Replace elements as follows:

• Put a new gasket on each element.

• Install into tank opening.

• Uniformly tighten element bolts. Torque to approximately

32 ft/lbs.

10. Connect element wiring as necessary.

11. Follow FILLING instructions to restore boiler to service.

• Check for water leaks around elements and proper

operation when boiler is filled.

• Replace insulation and cabinet panel.

CHECKLIST

Before calling for service, check the following points to see if the cause
of trouble can be identified and corrected. Reviewing this checklist
may eliminate the need of a service call and quickly restore the boiler
to service. The illustration on page 5 identifies the location of most of
the boiler components.

BE SURE TO TURN OFF THE ELECTRICITY WHEN CHECKING
EQUIPMENT.

Not enough or no heat

1. Be certain the electrical disconnect switch serving the boiler is in
the ON position. The pilot switch(es) on the cabinet front should
be on.

• In some installations the boiler electrical service may be

limited by the power company or boiler controls. If the
boiler operates on a controlled circuit heat may be
effected.

2. Check the fuses.

• The electrical disconnect switch usually contains fuses.

• The boiler has fuses located behind the cabinet door,

see page 5 for location.

3. If the water was excessively hot, and is now cold, the high
temperature cutoff may have operated (manual reset equipped
models).

• To reset, turn off electricity and remove the back panel

and push the reset button.

• Repeated operation of the high temperature cutoff should

be investigated by your servicer.

4. The capacity of the boiler may have been exceeded by a large
demand for heat.

• Large demands require a recovery period to restore

water temperature.

5. Sediment or lime scale may be affecting boiler operation. Refer to
MAINTENANCE for details.

Water is too hot

1. Refer to TEMPERATURE REGULATION.

Boiler makes sounds

1. Sediment or lime scale accumulation on the elements may cause
sizzling and hissing noises when the boiler is operating.

• The sounds are normal , however, the tank bottom and

elements should be cleaned. Refer to MAINTENANCE
for details.

2. Some of the electrical components of the boiler make sounds which
are normal.

• Contactors will “click” or snap as the boiler starts and

stops.

• Transformers and contactors often hum.

Water leakage is suspected

1. Check to see if the drain valve is tightly closed.

2. If the outlet of the relief valve is leaking it may represent:

• Excessive water pressure or air in the system.

• Faulty relief valve.

3. Examine the flange area of the elements and tank cleanout for
gasket leakage.

• Tighten the bolts or, if necessary, follow the WATER AND

LIME SCALE REMOVAL procedure to replace the
gaskets.

SYSTEM WATER TEST

System water test

Review SYSTEM CLEANING section, for a description of six problems
which result from loss of system chemical stability . Chemical stability
is checked by:

1. Draw off water from system. Is it dirty, discolored or odorous?

2. What is the pH of the system water? It should be neutral or slightly
alkaline.

3. Does “air” purged from system vents burn? If so, the “air” is actually
gas.

If any of the above conditions are present, all waterways should be
cleaned and the water adjusted to an alkaline condition.

If you cannot identify or correct the source of
malfunction:

1. Place the boiler electrical disconnect switch in the OFF position.

2. Close the make-up water inlet valve to the boiler.

3. Contact your servicer.

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NW-37 THRU NW-670 ELECTRIC HOT WATER BOILER LIMITED WARRANTY

A.O. Smith Corporation, the warrantor, extends the following LIMITED WARRANTY to the owner of this boiler.

1.

THE TANK

If the tank in this boiler shall prove upon examination by the warrantor to have leaked due to natural corrosion from water therein, during
the FIRST year after initial installation, the warrantor will at its option, repair it or provide a replacement tank less elements an d
controls of equivalent size and then current model. Some government agencies are requiring energy efficient standards for boilers. In the
event regulations prohibit sale of a model of equivalent size and construction, A.O. Smith will provide a model which complies with
the regulations of your area, in which case the consumer will be charged the difference in price between the like replacement and the
energy efficient model required. The warranty on the repair or replacement of the part, portion or tank will be limited to the unexpired
term of the original warranty.

2.

ALL OTHER PARTS

If within ONE year after initial installation of this boiler , any p art or portion shall prove upon examination by the warrantor to be defective in
material or workmanship, the warrantor will repair or replace such part or portion at its option.

3.

CONDITIONS AND EXPECTATIONS

This warranty shall apply only when the boiler is installed in accordance with local plumbing and building codes, ordinances and regulations,
the printed instructions provided with it and good industry practices. In addition, a pressure relief valve, approved by the American Society
of Mechanical Engineers, must have been installed.
This warranty shall apply only when the boiler is used:
a. (1) at temperatures not exceeding the maximum setting of its control;

(2) at water pressure not exceeding the working pressure shown on the boiler;
(3) when filled with water, free to circulate at all times and with the tank free of damaging scale deposits;
(4) in a noncorrosive and non-contaminated atmosphere;
(5) in its original installation location;
(6) in the United States, its territories or possessions, and Canada.
(7) when operated free of the damaging effects of uncontrolled thermal expansion and/or water hammer.

b. Any accident to the boiler, any misuse, abuse (including freezing) or alteration of it, any operation of it in a modified form will

void this warranty.

4.

SERVICE AND REPAIR EXPENSE

Under this limited warranty the warrantor will provide only repair or a replacement tank or part thereof. The owner is responsible for all
other costs. Such costs may include but are not limited to:
a. Labor charges for service, removal, repair, or reinstallation of the tank or any component part;
b. Shipping, delivery, handling, and administrative charges for forwarding the new tank or replacement part from the nearest

distributor and returning the claimed defective tank or part to such distributor.

c. All cost necessary or incidental for any materials and/or permits required for installation of the replacement tank or part.

5. LIMITATION ON IMPLIED WARRANTIES

Implied warranties, including any warranty of merchantability imposed on the sale of this boiler under state law are limited to one (1) year
duration for the tank or any of its parts. Some states do not allow limitations on how long an implied warranty lasts, so the above limitation
may not apply to you.

6.

CLAIM PROCEDURE

Any claim under this warranty should be initiated with the dealer who sold the boiler, or with any other dealer handling the warrantor’s
products. If this is not practicable, the owner should contact:

U.S. Customers Canadian Customers
A.O. Smith Corporation A.O. Smith Enterprises Ltd.
5621 W. 115th Street P.O. Box 310-768 Erie Street
Alsip, IL 60803 Stratford, Ontario N5A 6T3

a. The warrantor will only honor replacement with identical or similar tank or parts thereof which are manufactured or distributed

by the warrantor.

b. Dealer replacements are made subject to in-warranty validation by warrantor.

7.

DISCLAIMER

NO OTHER EXPRESS WARRANTY HAS BEEN OR WILL BE MADE IN BEHALF OF THE WARRANTOR WITH RESPECT TO THE
BOILER OR THE INST ALLATION, OPERATION, REPAIR OR REPLACEMENT OF THE TANK OR PARTS. THE WARRANTOR SHALL
NOT BE RESPONSIBLE FOR WATER DAMAGE, LOSS OF USE OF THE UNIT, INCONVENIENCE, LOSS OR DAMAGE T O PERSONAL
PROPERTY, OR OTHER CONSEQUENTIAL DAMAGE. THE WARRANTOR SHALL NOT BE LIABLE BY VIRTUE OF THIS WARRANTY
OR OTHERWISE FOR DAMAGE TO ANY PERSONS OR PROPERTY, WHETHER DIRECT OR INDIRECT, AND WHETHER ARISING
IN CONTRACT OR IN TORT.
a. Some states do not allow the exclusion or limitation of the incidental or consequential damage, so the above limitation or

exclusion may not apply to you.

b. This warranty gives you specific legal rights, and you may also have other rights which vary from state to state.

T elephone: 800-323-2636 T elephone: 519-271-5800

Fill in the following for your own reference. Keep it. Registration is not a condition of warranty. The model and ASME numbers are
found on the boiler’s rating plate.

Model No._______________________________________ASME No.___________________Date Installed__________________
Dealer’s Name____________________________________________________________________________________________
Dealer’s Address_____________________________________________________________Phone No.____________________

City and State_______________________________________________________________Zip___________________________

KEEP THIS WARRANTY AND MANUAL POSTED ADJACENT TO THE BOILER FOR FUTURE REFERENCE WHENEVER MAINTENANCE, ADJUSTMENT OR

SERVICE IS REQUIRED. BE SURE YOUR DEALER HAS FILLED IN THIS WARRANTY.

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