Hi Guys

I've got a very strange problem with a baxi 105e and need a little advice please.

The problem is that when the boilers is stone cold (first thing on a morning or after work on a evening) and the CH timing trys to fire up it gets a 'flame failure' fault on it..

Now, if I reset the boiler, turn on the hot tap, the boiler will fire up fine and I get hot water. If while the hot water is running I turn the CH on it will stay on! And when there is some heat in the system the CH will work from the timer just fine, until the morning or evening...

When the failure occurs (cold boiler) everything seams to work in the correct sequence, pilot rails light but go straight out!

I've replaced the CH temp sensor and DHW diaphragm in the diverter valve, still the same. I've prove out the microswitches & cleaned the combustion chamber..

Now if I go through the fault finding sequence off the Bxi pdf it points to the gas valve and/or PCB. I've sort of rueled out the gas valve as it works just fine on DHW so surely it only leaves the PCB?

Thanks in advance
Damien

ps.
I'm a fully qualified engineer (electrical and mechanical) and all gas, water and power were isolated while opening the combustion chamber...

I will not be changing any gas parts myself, I'm just trying to get a handle on what the problem could be.

Thanks

Scruff, where are you!!!

Damn, I thought you guys would know what it was straight off the top of your head

thescruff wrote on Dec 7^th, 2011, 5:49pm:


Thanks matey, appreciate it  

thescruff wrote on Dec 7^th, 2011, 9:41pm:


Thanks. The flame ignition looks to be working fine so I'll get someone to check out the high and low pressure.