BAXI System 35/60 Boiler fault. PCB?

[kmillar]

My BAXI System 35 boiler went on the blink today. It has been running well for 3 years now.

The fault lights suggest 'fault with fan/flue'. I have checked the fan is turning fine, and have checked that the micro-switch on the flu pressure sensor is operating correctly. I have also traced the wiring back from the microswitch on the pressure sensor to the PCB and that seems OK to.

My guess is that it must be the PCB which is faulty.

The symptoms are... After resetting the boiler and setting the CH Demand on, the boiler pump and fan run up, and after about 10 seconds the flu/fan fault light starts flashing. The pump and fan continue to run.

Should I go ahead and replace the PCB or could it be something else?

[Ed Sirett]

The key question is does the microswitch operate inside the 10 second window? If it does then the PCB is suspect. I expect that maybe cetltd has one.

If it doesn't then the problem might be that there is dirt near the inlet tube to the pressure switch. It might still operate but not quickly enough.

[geoff]

[kmillar]

I got a new board from

today - it cost =A372 + Vat and this has cured the problem. However I now have a new issue, which I think may be due to disturbed wiring. See me new post today 'Baxi system 35/60 Wiring'. The problem is that under CH demand the boiler operates perfectly. Under DHW demand the pump runs etc but the flame never lights.

Many thanks to those who helped!

-Kenny