CH limit stat should have continuity between 62 & 63 on PCB, check and rectify

test for 24 vAC between terminals 66 and 60. if not making, fan can be removed and fan implellers can be cleaned under a running tap (don't get motor wet observe safe working). bearings can be greased on fan. check APS tubes are ok and heat exchanger is clean

can be adjusted on PCB via potentiometer p2 if too hot

wires can be temporarily swapped between thermistors to check for faults.

Mode selection switch (Hot water, heating continuous, heating timed rotary selector) can get carbon build up on contacts at back of switch, try spraying contacts with WD40 or equivalent, may need new switch.

o-rings on secondary heat exchanger can become brittle and leak water. 3 packs are required to change all the o-rings

1. electrodes can bend towards burner when hot

2. restrictor fitted in flue can cause air pressure switch to drop out

3. Old honeywell gas valves had problems sticking, check label on side, if says 0-60 degrees C then these have been changed to -15 degrees to 45 degrees gas valves.

Check both fan venturis, can go brittle and prevent boiler from lighting

thermistors are prone to failure, check when hot 1000 ohms and cold roughly 13,000 ohms to 18,000 ohms.

Potentiometer knob stalk can snap at PCB

check ignition potentiometer setting on PCB may need increasing, adjust for a smooth ignition.

if fitted on a 4 inch vertical flue they normally always fail performance test. increasing to a 5 inch vertical fllue normally resolves

PCB needs telling this is a combi boiler, parameters need resetting to tell the PCB this has a pump (this PCB fits the conventional boiler aswell).

1. Hold down RESET & MODE for 3 Seconds

2. Use RESET to scroll through to setting 2

3. Press MODE to view the parameter

4. Adjust this setting to number 6 by turning the user heating control potentiometer (appliance type setting; 6= Combi, 2= Conventional

5. Press RESET&MODE keys together to save and exit

Check all sensors including flue sensor, if they are out of range then the boiler may think it is hot and the pump runs to dissipate the heat. Check for 15 kOhms Cold to approx 1000 Ohms Hot.

Appliance inoperative after new PCB, or power cut.

Boiler states low pressure but pressure ok

Parameters on PCB may need setting/rechecking as follows;

1. Press and hold RESET for up to 10 seconds, t5 displays, press RESET key once to enter parameters, P 01 will flash.

2. Use hot water + to enter parameter, then use hot water +/- to alter value

3. To go to the next parameter, use the heating +/-.

4. After adjusting parameters, hold the RESET button for up to 10 seconds to store the value

Parameters which may drift are;

P 01 is low pressure switch type, 0 is switch, 1 is sensor

P 02 is appliance type, 1 is standard combi, 2 is stored combi, 3 is system boiler

2 dashes is appliance turned off, press ECO for five seconds to turn back on.

FH is 120 seconds 1st air purge when powered up

D1 = How water satisfied, waiting for temperature drop before refiring

D2 = Heating satisfied, waiting for temperature drop before refiring

If fan is running even with no demand, suspect faulty Fan

If all is working ok but fan runs constantly after demand ends then maybe faulty primary sensor