Ariston A23 MFFI, A27 MFFI Servicing Instructions

A/23 MFFI - A/27 MFFI

G.C.N. 47-116-10 / 47-116-12
Servicing Instructions
Type C Boilers

LEA VE THESE INSTRUCTIONS
ADJACENT T O THE GAS METER

2

B029

Page No.

1. SERVICING INSTRUCTIONS

1.1 Replacement of Parts 3

1.2 To Gain General Access

- Removing the Front Panel 3

- Removing the Side Panels 4

- To Lower the Control Panel 4

1.3 Access to the Combustion Chamber

- Removing the Sealed Combustion Chamber 5

- Removing the Burner and Injectors 5

- Removing the Electrodes 6

- Removing the Main Heat Exchanger 7

- Removing the Air Pressure Switch 7

- Removing the Venturi Device 8

- Removing the Fan 8

1.4 Servicing and Removal of the Gas Valve

- Setting Gas Pressure 9

- Removing the Spark Ignitor 11

- Removing the Gas Valve 12

1.5 Access to the Hydraulic Circuit

- Removing the D.H.W. (Secondary) Exchanger 12

- Removing the Safety Valve 13

- Removing the Automatic Air Vent 13

- Removing the Main Flow Circuit Switch 13

- Removing the Pump 14

- Removing the Pressure Gauge 14

- Removing the Expansion Vessel 15

- Removing the Overheat Ther mostat 15

- Removing the Heating Temperature Sensor (N.T.C.) 15

1.6 Access to the Control System

- Checking the Fuses 16

- Removing the Time Clock 16

- Removing the P.C.B.s 17

2. FAULT FINDING

2.1 Fault Finding Guide (Flow-chart) 18

2.2 Fault Finding Using the Total Check System 23

3. ELECTRICAL DIAGRAMS

3.1 Electrical Connection 24

3.2 Functional Flow Connection 25

4. SHORT SPARE PARTS LIST

26

TABLE OF CONTENTS

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B029

1. SERVICING INSTRUCTIONS

The life of individual components vary and they will need servicing or
replacing as and when faults develop.
The fault finding sequence chart in chapter 2 will help to locate which
component is the cause of any malfunction, and instructions for removal,
inspection and replacement of the individual parts are given in the following
pages.

1.1 Replacement of Parts

1.2 To Gain General Access

All testing and maintenance operations on the boiler require the control panel
to be lowered.This will also require the removal of the casing.

To dismantle the front part of the casing, proceed as follows:

1.

Remove screw “A”

(see fig. 1.1)

;

2.

Lift the front panel up and forward

(see fig. 1.2)

.

A

Fig. 1.2

Fig. 1.1

To ensure efficient safe operation, it is recommended that the boiler is
serviced annually by a competent person.

Before starting any servicing work, ensure both the gas and electrical
supplies to the boiler are isolated and the boiler is cool.

Before and after servicing, a combustion analysis should be made via the flue
sampling point (please refer to the Installation Manual for further details).

After servicing, preliminary electr ical system checks must be carried out to
ensure electrical safety (i.e. polar ity, earth continuity, resistance to earth and
short circuit).

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B029

Removing the side panels

1.

Remove the screws “B”;

2.

Pull the panel away from the boiler, then lift the panel
up and away from the boiler

(see fig. 1.2).

To lower control panel

1.

Remove the screws “B”

2.

Push the two side panels outward slightly

(fig. 1.5)

;

3.

Rotate the control panel forward and down.

Fig. 1.4

B

Fig. 1.5

B

C

Fig. 1.7

Fig. 1.6

C

To access the areas where the adjustment and control devices are located,
simply remove the plugs by pressing from the inside, unscrew the screws “C”
and remove the bottom part of the instrument panel, rotating it upwards.

Fig. 1.3

B

1.

Remove the side panels of sealed chamber

(fig. 1.10)

;

2.

Remove the screws “F” of the burner

(see fig. 1.11)

;

3.

Remove the burner

(see fig. 1.12)

;

4.

Remove the injectors using a No. 7 socket spanner;

5.

Replace in reverse order.

Removing the burner and the
injectors

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B029

Removing the sealed chamber

frontal cover

1.3

Access to the Combustion Chamber

Remove the screws “D”

Remove the screws “E”

Removing the combustion cover

E

E

E

E

E

E

E

Fig. 1.8

Fig. 1.9

D

D

D

D

Fig. 1.10

Fig. 1.11

Fig. 1.12

F

push

push

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B029

Removing the electrodes 1.

Remove rubber gasket “G”

(see fig. 1.13)

;

2.

Disconnect ignition leads by pulling downward

(see fig. 1.14)

;

3.

To remove the flame sensor, disconnect the cable at its only connection
point close to the P.C.B.

(see fig. 1.15)

;

5.

Remove screw “H” using a Philips No.2 star tip screwdriver

(see fig. 1.16)

;

6.

Slide the electrode gently downward

(see fig. 1.17).

To replace, repeat the steps in reverse order , pa ying particular attention to the
following:

a

-Centre the electrode in the positioning hole carefully, otherwise the
electrode may break;

b

-Check that the cables have been connected correctly;

c

-Check that the rubber gasket covers the cable/electrode connection

point completely.

Fig. 1.13

G

Fig. 1.14

Fig. 1.15

Fig. 1.16

Fig. 1.17

H

1.

Disconnect the electrical connections “K” and silicone pipes “L” from their
connection points

(see fig. 1.20)

;

2.

Remove screws “J” on the top of the sealed chamber

(see fig. 1.21)

;

Use a No.2 star tip screwdriver to remove the switch from the plate.

Fig. 1.21

Fig. 1.20

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B029

1.

Drain the boiler of water;

2.

Release the two connection nuts “I” connecting the exchanger to the flow
and return pipes

(see fig. 1.18)

;

3.

Pull it straight out

(see fig. 1.19).

Removing the main heat
exchanger

Removing the air pressure switch

Fig. 1.18

I

Fig. 1.19

L

L

K

J

J

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B029

1.

Disconnect the silicone pipes “M” and remove the screw “N”

(see fig. 1.22)

;

2.

Extract the venturi

(see fig. 1.23)

.

Removing the venturi device

1.

Disconnect electrical connections and remove screws
“O” using a No. 2 star tipped screwdriver

(see fig.1.24)

;

2.

Pull fan to the right, forward and remo ve (

see fig.1.25)

;

3.

Remove fan from mounting plate;

4.

Remove screws “P”

(see fig.1.26)

.

Removing the fan

M

N

Fig. 1.22

Fig. 1.23

Fig. 1.24

Fig. 1.25 Fig. 1.26

O

O

P

P

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B029

1.4

Servicing and Removal of the Gas Valve

1

2

3

4

A

B

C

E

F

D

SIT
TANDEM

SIT
SIGMA

1

2

3

4

A

B

C

E

F

D

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B029

Setting the minimum and the maximum power of the boiler

1. Check that the supply pressure to the gas valve is a minimum of 20 mbar

for natural gas.

2. To do this, remove the screw “A”.
Fit the pipe of the pressure gauge to the pressure connection of the gas
valve “B”.
When you have completed this operation, replace the screw “A” securely
into its housing to seal off the gas.

3. To check the pressure supplied by the gas valve to the burner, remove the
screw “C”. Fit the pipe of the pressure gauge to the pressure outlet of the
gas valve “D”.
Disconnect the compensation pipe either from the gas valve or from the
sealed chamber.

4. Set the On/Off button to position < I > and the "summer/winter" switch to
the winter position.
To set the maximum power, turn on the hot water tap and allow the hot
water tap to run at a rate of about 8 litres/minute so that the main burner
lights.
Adjust nut “E” on the modureg to set the gas pressure (displayed on the
pressure gauge) corresponding to the maximum power (see table “A”page 11).

5. T o set the minim um pow er, disconnect a supply terminal from the modureg
and adjust screw “F”.
Turn the screw clockwise to increase the pressure and coun­ter-clockwise to decrease the pressure (displayed on the
pressure gauge) corresponding to the minimum power (see table “A” page

11).

6. When you have completed the above operations, turn off the
hot water tap, re-connect the supply terminal to the modureg
on the gas valve and replace the cap on the screw of the
modureg.

Setting the maximum heating circuit power

7. To set the maximum heating circuit power, place the

On/Off button to position < I > and the "summer/winter" switch to winter
position.
Turn the knob of the heating ther mostat clockwise to maximum;

8. Remove the left hand inspection panel of the P.C.B. and fit a small

cross-head screwdriver in to the right hand potentiometer.Turn clockwise
to increase the pressure or counter-clockwise to reduce the pressure.
Adjust the setting to the required heating pressure value (displayed on the
pressure gauge), as indicated in the diagrams shown in page 11.

9. Turn off the boiler by placing the main switch to the "Off" position.

Setting pressure for soft ignition.

Disconnect the detection electrode connection from the P.C.B. (see fig.

1.13).
Start the boiler and during the ignition sequence adjust the centre
potentiometer until the gas pressure reads the required gas pressure as
per the table below.
Once the gas pressure is set turn off the boiler and reconnect the
connection to the P.C.B.
NB.:It may be necessary to reset the flame failure reset a number of times
during this operation.

Setting gas pressures

Recommended pressure for
slow ignition

NATURAL GAS (G20) BUTANE GAS (G30) PROPANE GAS (G31)

5 mbar - 1.95 in w.g.

18 mbar - 7.0 in w.g. 19 mbar - 7.4 in w.g.