Vokera Excell 80SP - burner doesn't re-ignite

[Antony2008]

Good Morning All.

In ch+dhw mode, when there is an initial call for heat the burner ignites without problem and heats for around five minutes or so. After this, the burner goes out with the pump continuing to circulate. The temperature at this point has risen to 60°C, with the system pressure at 2bar.
I've waited the obligatory three minutes in-built delay timer before re-ignition (although to my mind the burner shouldn't have gone out as the set temperature hadn't been reached) yet the boiler just sits there pumping the now cooling water around the radiators. Incidentally, under these conditions, a call for dhw energises the fulcrum arm and dhw micro switch yet the burner still doesn't ignite.
Switching the mode selector switch from ch+dhw to dhw only, then back again to ch+dhw (nine times out of ten) gets the boiler to re-ignite immediately.

I'd very much appreciate it if someone could point me in the direction of what to fix/replace.

Thanks in advance.

Antony

 

[Rob]

Id imagine its an airflow fault. Probably due to lack of servicing, because of the permanent pilot the boiler fan needs to run all the time so they get particlaly dirty inside.

Not the sort of area a DIYer should be touching.

 

[bellairaphon]

sounds like micro switch or stuck in central heating mode excell service kits should sort it...

 

[DP]

I suspect it is your PCB.

When boiler sequence begins, path is set up for gas valve to operate.

When boiler has reached temperature set, gas valve drops out for three minutes. At the end of the anticycling delay, reoperate path for gas valve is missing due to possible relay contact erosion. switching the boiler off and then on, gets the boiler going as sequence of operation begins from beginning instead of somewhere in the middle.

Do not change the PCB just because I said so, get the meter out and look for voltages. Circuit diagram in the manual is quite good.

Boiler should reach 85 degrees when CH stat set at max. Burner should 'step down' to low flame as desired control set temperature is approached. A boiler service will certainly improve boiler operation. Have never had to use the service kit as I usually carry individual components. I suspect the service kit is intended for the end user or for occasional tussle with the boiler. Boiler makes seem to be geographic thing. While for me almost every second or third boiler is a Vokera, other hardly ever come across one.