All Working but No Gas to Light for CH

[cheapsk8]

Hi
Saunier Duval SD620/05F2 old as the hills. Was working generally OK until Sunday. Heating came on as usual, radiators warm, everything okaydokee. Then noticed room got cold and raditors very cold. The boiler was running but the the burner was not lit, pilot light was lit.

Burner comes on OK for the HW but not for the CH.
Checked the flu pressure switch operation.
Checked the CH water presure OK @ 1bar and the gauge moves if you fill abit or drain abit.

However the the big knob on the front only clicks once when turn fully in either direction, and I thought it used to click twice.

Is it a faulty temperature sensor - and if so how do I check, or is it the big knob control and/or board and if so is it still available.

Hope I've covered all the information you need. Thanks inadvance.

 

[cheapsk8]

I've replaced the High temp sensor (on the LHS of the heat exchanger) and now I've got 2 clicks when I turn the big knob.

But other than that the boiler is doing just what it did before - HW is fine, but the CH is just circulating the water through the exchanger with the extraction fan running but no gas lit. So the radiators are now just as cold as outside.

I'm looking for help here guys.

Thanks inadvance.

 

[Soggy_weetabix]

Poor quality boilers im afraid with equally poor components.

I know very little about these boilers as I generally refuse to work on them but I would suspect a divertor valve fault.

Maybe one of the experts on here has more experiance and can give you more advice.

David

 

[cheapsk8]

Hi David

Thanks for your input - I was begining to think nobody loved me

If it's the diverter value - can you explain how this tells the gas solenoid not to fire? I'm not sure I understand.

Thanks

 

[Soggy_weetabix]

Hi David

Thanks for your input - I was begining to think nobody loved me

If it's the diverter value - can you explain how this tells the gas solenoid not to fire? I'm not sure I understand.

Thanks

Its not you, its the 'sunny D' boiler you have.

Power to the solenoid does not come from the divertor valve. It will divert the water through the secondry heat ex for h/water demand and the c/heating circuit on demand for heat. Different components will tell your boiler to fire.

It appears your boiler will not circulate water through the heating circuit.

Diverters can be repaired but I have very little knowledge of this boiler to tell you if its possible.

Only if your in South Beds / East Bucks / North Herts could I reccommend a Sunny D expert.

David

 

[cheapsk8]

David

Thanks for the explanation - seems to suggest the problem is not the diverter valve.

The pump is circulating water through the heat exchanger just fine. The evidence for this is that the radiators are as cold or colder than outside because the heating has been running without any gas lit (permanent pilot is lit). So the CH water is being child by the flu extraction fan.

The problem now I feel must lie either with the pressure sensor (different to the functioning gauge) or the control board or control knob.

Its not the solenoid or temperature sensors because the HW fires up just dandy.

Thanks for for help - Its clarified my thoughts and it always helps to bounce ideas.

Cheers
Nigel[/quote]

 

[cheapsk8]

Its not you, its the 'sunny D' boiler you have.

Power to the solenoid does not come from the divertor valve. It will divert the water through the secondry heat ex for h/water demand and the c/heating circuit on demand for heat. Different components will tell your boiler to fire.

It appears your boiler will not circulate water through the heating circuit.

Diverters can be repaired but I have very little knowledge of this boiler to tell you if its possible.

Only if your in South Beds / East Bucks / North Herts could I reccommend a Sunny D expert.

David

Well seems that you were sort of right & you get credit for pointing me in the right direction.

There are 3 mircro switches on top of the diverter valve, and although the connections & wires are sound, one of the switches or it's mounting is suspect. Will investigate fully in the spring - in the meantime I'm nice and toastie.

Sorry it took so long to report back and thanks for your help anyway.