On Jan 3, 6:56*pm, Ed Sirett wrote:
On Thu, 03 Jan 2008 08:54:32 -0800, kmillar wrote:
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?

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.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is athttp://www.diyfaq.org.uk
Gas fitting FAQ *http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQhttp://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQhttp://www.makewrite.demon.co.uk/BoilerChoice.html

Yes the switch operates within the 10 second window.
I got a new board from http://www.heatcel.co.uk/ today - it cost £72 +
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