combi 80 not sensing flame on CH

[willhamlyn]

Hi I have a combi 80 which is locking out on CH demand, it ignites fine but the flame LED doesn't come on, leading to a lockout a few seconds later

It's fine with HW, ignites normally and flame light comes on as normal. I checked the sensor connection on the full sequence board anyway, which all seems fine.

Would this point to the full sequence board being faulty? I'm assuming if the sensor picks up the HW flame it must be fine otherwise it would lockout then as well? I checked it with a voltmeter and at idle it reads 50 volts which rises to around 95 when ignited before it locks out.

The board is about the only part that hasn't been replaced (dates from 1998 )

As it's been warm we haven't used the CH in a few months.

Thanks.

Will.

 

[filsyn]

You may need to adjust the flame rectification probe, it works OK on DHW because it goes straight into full burner and when there is a demand for CH it isn't sensing it in low burner, I've had this once before.

 

[willhamlyn]

Actually having just tried to run a bath it appears the DHW will only run for about 90 seconds to 2 minutes before the flame goes out and it locks out.

Would that point to the board or the electrode? Presumably electrode is Gas Reg only?

 

[filsyn]

Actually having just tried to run a bath it appears the DHW will only run for about 90 seconds to 2 minutes before the flame goes out and it locks out.

Would that point to the board or the electrode? Presumably electrode is Gas Reg only?

It's probably going to lock because when the DHW modulates to low flame it isn't sensing the low flame. If you're not gas safe registered call someone in who is and explain this may be the fault, if this is the fault (and thats what seems to be happening) then it will only take him a short time to rectify your flame rectification probe.

 

[willhamlyn]

Ah I see what you mean, yep that makes sense, time to give my local friendly boiler man a call tomorrow.

Many thanks for the advice.

Will.