A.O. Smith VWH 500, VWH 200 Technical Documents

VFS-SER Rev A

Service Manual

Models: 500 - 2000

Up To 4:1 Turndown

Setup/Return

 WARNING

Save/Clear

Run/Stop

This manual must only be used by a qualified heating installer / service technician. Read all instructions, including this manual and the VF Series Installation and Operation Manual, before installing. Perform steps in the order given. Failure to comply could result in severe personal injury, death, or substantial property damage.

Save this manual for future reference.

Contents

CONTENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Hazard Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

PLEASE READ BEFORE PROCEEDING . . . . . . . . . . . . . 3

Handling Ceramic Fiber Materials . . . . . . . . . . . . . . . . . . . 3

When servicing appliance . . . . . . . . . . . . . . . . . . . . . . . 3

Appliance operation . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Appliance water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

WHAT IS IN THIS MANUAL . . . . . . . . . . . . . . . . . . . . . . . 4

1. SERVICE

The VF Series Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Control Module Inputs . . . . . . . . . . . . . . . . . . . . . . . . . 6

Control Module Outputs . . . . . . . . . . . . . . . . . . . . . . . . 7

General Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Sequence of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Display Panel Menu Access . . . . . . . . . . . . . . . . . . . . . . 10

Display Panel Parameter Access . . . . . . . . . . . . . . . . . . . 11

Parameter Table. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Viewable and Changeable Control Parameters . . . . . 13-15

2. MAINTENANCE

Maintenance and Annual Startup . . . . . . . . . . . . . . . . 16-24

3. TROUBLESHOOTING

Before Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Check Control Module Fuses . . . . . . . . . . . . . . . . . . . . . 25

Table 3A - Troubleshooting Chart - No Display . . . . . . . . 26

Checking Temperature Sensors . . . . . . . . . . . . . . . . . . . 27

Table 3B - Inlet/Outlet Resistance vs. Temperature . 27 Table 3C - Flue Temperature Sensor Resistance vs.

Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Table 3D - Tank Sensor Resistance vs. Temperature 27

Table 3E - Troubleshooting Chart - Noisy System . . . . . 28

Table 3F - Troubleshooting Chart - Fault Messages . 29-35

Revision Notes . . . . . . . . . . . . . . . . . . . . . . . . . Back Cover

Hazard definitions

The following defined terms are used throughout this manual to bring attention to the presence of hazards of various risk levels or to important information concerning the life of the product.

 DANGER

 WARNING

 CAUTION

CAUTION

NOTICE

DANGER indicates an imminently hazardous situation which, if not avoided, will result in death or serious injury.

WARNING indicates a potentially hazardous situation which, if not avoided, could result in death or serious injury.

CAUTION indicates a potentially hazardous situation which, if not avoided, may result in minor or moderate injury.

CAUTION used without the safety alert symbol indicates a potentially hazardous situation which, if not avoided, may result in property damage.

NOTICE indicates special instructions on installation, operation, or maintenance that are important but not related to personal injury or property damage.

Please read before proceeding

Service Manual

 WARNING

NOTICE

Installer – Read all instructions, including this manual and the VF Series Installation and Operation Manual, before installing. Perform steps in the order given.

User – This manual is for use only by a qualified heating installer/service technician. Refer to the VF Series Installation and Operation Manual for your reference.

Have this appliance serviced/inspected by a qualified service technician at least annually.

Failure to comply with the above could result in severe personal injury, death or substantial property damage.

When calling or writing about the appliance – Please have the appliance model and serial number from the appliance’s rating plate.

Consider piping and installation when determining appliance location (see the VF Series Installation and Operation Manual).

Any claims for damage or shortage in shipment must be filed immediately against the transportation company by the consignee.

When servicing appliance –

• To avoid electric shock, disconnect electrical supply before performing maintenance.

• To avoid severe burns, allow appliance to cool before performing maintenance.

Appliance operation –

• Do not block flow of combustion or ventilation air to the appliance.

• Should overheating occur or gas supply fail to shut off, do not turn off or disconnect electrical supply to circulator. Instead, shut off the gas supply at a location external to the appliance.

• Do not use this appliance if any part has been under water. The possible damage to a flooded appliance can be extensive and present numerous safety hazards. Any appliance that has been under water must be replaced.

Appliance water –

• Thoroughly flush the system (without appliance connected) to remove sediment. The high-efficiency heat exchanger can be damaged by build-up or corrosion due to sediment.

• Do not use petroleum-based cleaning or sealing compounds in the appliance system. Gaskets and seals in the system may be damaged. This can result in substantial property damage.

• Do not use “homemade cures” or “appliance patent medicines”. Serious damage to the appliance, personnel, and/or property may result.

What is in this manual?

Service Manual

Service

The VF Series display

• Display panel readout, buttons and their functions

Control module inputs

• Control module inputs and options

Control module outputs

• Control module outputs and options

General

• How the appliance operates

• How the control module operates

• Access modes -- user and installer

• Sequence of operation -- Domestic Hot Water (DHW)/space heating

Control panel menu access

• Accessing programming mode and locating menus

Control panel parameter access

• Accessing and changing parameters from the display panel

Maintenance

• Service and maintenance schedules

• Address reported problems

• Inspect appliance area and appliance interior

• Clean condensate system

• Check all piping for leaks

• Flue vent system and air piping

• Check water system

• Check expansion tank

• Check control settings

• Check igniter

• Check all appliance wiring

• Check flue gas passageways

• Flame inspection

• Inspect and clean burner

• General maintenance

• Checking manifold gas pressure

• Combustion analysis procedure

• Gas valve adjustment procedure

• Cleaning heat exchanger

• Review with owner

Troubleshooting

Quick start information -- parameter table

• An index of available adjustments and readouts, where to access them and where to find detailed information.

VF Series operation

• A: General

• B: Data Logging

• C: Functions

• D: DHW Settings

• E: Control Modes

• F: Building Management System (BMS)

• G: Circulation Pump

• H: Service Notification

• Troubleshooting table - No display

• Checking temperature sensors

• Troubleshooting table - Noisy system

• Troubleshooting table -Fault messages displayed on Operator Interface

1 Service

The VF Series display

SETUP/RETURN

SAVE/CLEAR

RUN/STOP

Service Manual

BACK

FORWARD

1 Service

Control inputs

(FIELD SUPPLIED)

(FACTORY SUPPLIED)

ON/OFF / 0-10V

Service Manual

(FIELD SUPPLIED)

1 Service (continued)

Control outputs

Service Manual

(FIELD SUPPLIED)

(IF EQUIPPED)

1 Service

General Operation

Service Manual

How the appliance operates

The water heater uses a copper-finned tube heat exchanger to transfer heat from the flue products to the water. An electronic control module monitors various inputs to initiate a call for heat. The blower provides both primary and secondary air to the burner and forces the flue products out of the combustion chamber and into the vent system. The control module regulates the blower speed to control the firing rate of the appliance. The modulating gas valve monitors the amount of combustion air being pulled into the blower and regulates the amount of gas supplied, which then mixes with the combustion air and is supplied to the burner.

How the control module operates

The VF Series control module receives input from appliance sensors. The control module activates and controls the blower and gas valve to regulate heat input and switches the DHW pump on and off as needed. The user/installer programs the module to meet system needs by adjusting control parameters. These parameters set operating temperatures and heater operating modes. Appliance operation can be based on heater return water temperature, tank temperature, tank temperature thermostat, and/or remote enable switch.

Sequence of operation

Access modes

User

The user can adjust the tank setpoint using the (+) and (-) buttons at any time during normal operation. By entering the USER code (0101), the user can also change temperature units, time and date, and night setback settings. In user mode, the following parameters can be viewed but not changed: heater model number; software version; total operating hours, total cycles and last 10 faults.

Installer

Most parameters are available only to the installer, accessible only by entering the installer access code (2525).

Saving parameters

To save parameters and exit programming:

Press the SAVE/CLEAR button, then the SETUP/RETURN button 3 times.

To keep parameter settings only for a current operating cycle:

Press the SETUP/RETURN button 3 times after making all desired parameter changes.

Table 1A shows control module normal sequences of operation for DHW operation.

To enter a parameter and continue programming:

Press the SETUP/RETURN button 1 time to return to the parameter listings; press again to return to the menu listings. Remember to press the SAVE/CLEAR button when finished programming in order to save the changes made.

1 Service (continued)

Sequence of operation

Table 1A_Sequence of Operation - Space Heating and DHW

OPERATION DISPLAY

Service Manual

1. The manual reset high limit must be closed before any action will take place.

2. Upon a call for heat the control turns on the DHW pump. The flow switch and low water cutoff (if equipped) must close.

3. • The gas pressure switch(es) (if equipped) must close.

• The contacts for the louvers close. The louver proving, blocked drain switch, and auto reset high limit inputs must close.

• If the air pressure switch is open, the prepurge cycle then begins by starting the combustion blower. Once started, the air pressure switch must close.

4. After prepurge, the blower slows down and the hot surface igniter (HSI) is energized.

5. Once the HSI is hot, the trial for ignition begins with the opening of the gas valve.

6. If the control does not sense flame, it will lock out.

HTR: Standby OUT: 123.8F(129)

HTR: PREPURGE OUT: 123.9F(129)

HTR: IGNITION OUT: 123.9F(129)

HTR: POSTPURGE, LOCKOUT OUT: 123.9F(129)

7. If the control senses flame, it will fire the burner to maintain the setpoint. The firing rate will modulate as required to hold the tank temperature at the setpoint.

8. Once the call for heat is satisfied, the control will turn off the burner. The blower will remain on for the postpurge cycle. The DHW pump will continue to run for its pump delay time, then turn off.

9. Pump off.

HTR: DHW 20% RATE OUT: 124.8F(129)

HTR: POSTPURGE

OUT: 127.4F(129)

HTR: Standby

OUT: 124.7F(129)

1 Service

Display panel menu access

Table 1B_Use this procedure to access menus from the display panel

SAVE/

CLEAR

SETUP/

RETURN

Service Manual

(+)

FORWARD

(+)

FORWARD

(+)

FORWARD

(+)

SAVE/

CLEAR

SAVE/CLEAR

he FORWARD and BACK buttons

(+)

(-)

SAVE/CLEAR

Service Manual

1 Service (continued)

Display panel parameter access

Table 1C_This is a typical example of accessing a parameter, shown for pump delay parameter

(-)

SAVE/

CLEAR

SAVE/

CLEAR

(+)

(-)

SAVE/

CLEAR

SETUP/

RETURN

SETUP/

RETURN

30 sec

45 sec

The DHW Pump Delay menu item is shown

The DHW Pump Delay setting is shown

The new setting is saved and the menu item is shown

DHW

+ 25 hidden pages