Combi 77ff


Problem Solution
ignition problems/pilot Run hot water tap, fan runs for 30 secs, depress gas valve button fully, pilot should light,if not then check voltage to spark generator, also air pressure switch may not be giving full continuity. Check and rectify
Fan runs no power to gas valve

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

to test if Air pressure switch is made

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

Hot water adjustment

can be adjusted on PCB via potentiometer p2 if too hot

testing thermistors

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

Heating intermittent

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.


Combi 24B Combi f30B


Problem Solution
blowing fuses water can drip from combustion box through grommet onto pump and blow internal PCB fuse
water leaks

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


Modena 80e Modena 102


Problem Solution
Lockout issues

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.

Fan runs no ignition

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

cycling on off

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

No heating

Potentiometer knob stalk can snap at PCB

spark no gas/lockout

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

poor/failing performance test vertical flue

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


Optima 701


Problem Solution
low water pressure switch on later models a low water pressure switch was fitted which was not detailed in manufacturers instructions. please check for continuity


Optimax 25C


Problem Solution
No power to pump. overheating, bumping and banging

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

Pump constantly running, may give O/L fault

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.



Optimax HE 31C Opimax HE 38C


Problem Solution

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

Display symbols

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

Fan running, no ignition

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