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Andrew Smith
Andrew Smith, Engineer
Category: UK Plumbing
Satisfied Customers: 3629
Experience:  Domestic Gas, Commercial Gas, LPG, Unvented Hot Water, Part P Electrical, Commercial Catering
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Hi, Baxi Solo WM 40/4 PF, on heating demand, fan runs lights

Resolved Question:

Baxi Solo WM 40/4 PF, on heating demand, fan runs lights pilot and main burner OK, then very occasionally, within 5-30 seconds, main burner cuts out, boiler continues to run with all indicator lights illuminated. Remains stuck in that condition until heating demand removed then invariably starts and runs OK from next heating demand. Fault occurs a few times a week, sometimes not at all.
Cleaned Pilot Burner, checked electrode gap as being 4mm, control board replaced, also pressure sensor and checked all electrical connections in junction box.
Any ideas welcome!
Submitted: 5 years ago.
Category: UK Plumbing
Expert:  Andrew Smith replied 5 years ago.
Hi my name is XXXXX XXXXX lets see if we can get you sorted in the shortest possible time. When the boiler drops out, how many lights are left on?
Customer: replied 5 years ago.

Hi Andrew


Lights illuminate right to left, 3,2,1(although light 1 is fairly dim). All lights remain unchanged from nrmal rnnin when boiler drops out.

Expert:  Andrew Smith replied 5 years ago.
Ok, with all the lights lit, then it rules out the fan, APS and the thermostat. If it drops out can you hear it ticking like when it tries to light?
Customer: replied 5 years ago.
No ticking, doesn't try to light and just runs with no burner while the heat demand remains. If the CH or HW on the programmer is turned off, the boiler shuts down. On turning the CH or HW on again, assuming there is a heat demand the boiler fires and runs fine usually. The fault does seem to be more apparent when the boiler has already run and is hot.
Expert:  Andrew Smith replied 5 years ago.
It sounds like a sticking gas valve. To confirm this if you have a meter then leave it on the main gas valve connections and test the voltage when it is faulty. If there is voltage and the gas drops out then it is definitely a gas valve fault.
Customer: replied 5 years ago.
Have tried that, voltage is gone from gas valve solenoid coil, hence why I replaced the board.
Expert:  Andrew Smith replied 5 years ago.
Can you take the lead off the valve and check voltage there, then check the voltage straight off the board to rule out the wiring harness.
Customer: replied 5 years ago.

Yes good thought, will look at that. The crimps looked OK when switching the board but might be fractured beneath the insulation.


I've just fitted a new Pilot assembly and noticed the injector jet on the new assembly butts against an internal circlip, which had corroded away on the old Pilot and allowed it to move further down the pilot housing. Had noticed the gas pipe to the Pilot was loosening over a few days so this needed replacing anyway, it could be the fault but am doubtful as don't understand why the boiler doesn't attempt relight (no ticking) if the pilot is a problem, just a clunk from the gas valve as it goes off.

Expert:  Andrew Smith replied 5 years ago.
Like you say, if the pilot goes out it will continue to "tick" until it relights, also you would lose your 3rd light.
Customer: replied 5 years ago.
OK thanks, XXXXX XXXXX through the wiring tomorrow evening and report back
Expert:  Andrew Smith replied 5 years ago.
No problem
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