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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Plumbing Questions >> Baxi 105e Combi CH fault (only when boiler is cold https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1323213947 Message started by Damoegan on Dec 6^th, 2011, 11:25pm

Title: Baxi 105e Combi CH fault (only when boiler is cold
Post by Damoegan on Dec 6^th, 2011, 11:25pm

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

Title: Re: Baxi 105e Combi CH fault (only when boiler is cold
Post by Damoegan on Dec 7^th, 2011, 8:50am

Any thoughts guys?

Title: Re: Baxi 105e Combi CH fault (only when boiler is cold
Post by TIMBA-WOLF on Dec 7^th, 2011, 12:29pm

Scruff, where are you!!!

Title: Re: Baxi 105e Combi CH fault (only when boiler is cold
Post by thescruff on Dec 7^th, 2011, 4:48pm

No idea Wolfie :-*

Sounds like something is sticking when the boiler is cold, could be the gas valve, pump perhaps.

Needs an RGI to look at it when the boiler is cold, and hopefully he'll put his finger on it straight away.

Title: Re: Baxi 105e Combi CH fault (only when boiler is cold
Post by Damoegan on Dec 7^th, 2011, 5:30pm

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

Title: Re: Baxi 105e Combi CH fault (only when boiler is cold
Post by thescruff on Dec 7^th, 2011, 5:49pm

Nope, Ill put the question to the baxi man and see what he says.

Title: Re: Baxi 105e Combi CH fault (only when boiler is cold
Post by Damoegan on Dec 7^th, 2011, 7:02pm

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

Nope, Ill put the question to the baxi man and see what he says.

Thanks matey, appreciate it [smiley=thumbsup.gif]

Title: Re: Baxi 105e Combi CH fault (only when boiler is cold
Post by thescruff on Dec 7^th, 2011, 9:41pm

You need to get an RGI to check the high and low pressures, and the flame/ignition.

Title: Re: Baxi 105e Combi CH fault (only when boiler is cold
Post by Damoegan on Dec 7^th, 2011, 10:22pm

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

You need to get an RGI to check the high and low pressures, and the flame/ignition.

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

Title: Re: Baxi 105e Combi CH fault (only when boiler is cold
Post by thescruff on Dec 7^th, 2011, 10:27pm

he should also check the gas valve and the gas governor on the meter.