Oil boiler won't stop

[Over heated]

My Worcester Bosch external Camry oil boiler cannot be switched off by either my timer or the room thermostat. Both devices are Honeywell and the problem has arisen in the past couple of months after 9 years of problem-free operation. I have reset the wireless thermostat HCW80 and re-linked it to the receiver HC60. All flashing lights indicate that the receiver is getting a signal from the thermostat. I turn the stat down to 10C and the boiler stays on.

My next stop was to switch off the timer, Honeywell ST9400C. This did not stop the boiler. I then removed the timer from its base plate and the boiler is still firing.

Worcester Bosch say the boiler frost thermostat is not the problem because it does not control the central heating pump.

Any thoughts?

 

[Dan Robinson]

Zone valve

 

[Over heated]

Thanks, Dan. All the zone valves are working correctly. I called Honeywell and they suspect the wireless receiver has developed a fault. A replacement has been ordered.

 

[leakydave]

FROST STAT!!!! It is an External Boiler with a frost stat. Maybe this was calling for heat from the permanent live feed to the boiler.

 

[45yearsagasman]

How did you confirm that your zone valves are ok?

 

[Terrywookfit]

Learn how to use a multimeter!

If the frost stat activates, It will put a voltage on the S/L terminal which activates the pump.

 

[oilboffin]

Only one valve on camray actuator stuck hsa3cd or frost stat gone.Bob

 

[oilhead]

He has not said it is a combi. That would put a different complexion on the fault.

 

[Over heated]

I checked the valves by pushing the levers - on the odd occasion when the boiler did switch off, the levers for central heating and hot water were stiff. Worcester Bosch say that when the frost stat works it does not actuate the central heating pump. The Worcester Bosch engineer (who has been 5 times!) says the frost stats are indestructible and he has never known one to malfunction. Anyway, he has ordered a replacement. And the boiler is not a combi.

 

[Terrywookfit]

I checked the valves by pushing the levers - on the odd occasion when the boiler did switch off, the levers for central heating and hot water were stiff. Worcester Bosch say that when the frost stat works it does not actuate the central heating pump. The Worcester Bosch engineer (who has been 5 times!) says the frost stats are indestructible and he has never known one to malfunction. Anyway, he has ordered a replacement. And the boiler is not a combi.

The only things that can cause this are sticking zone valve switches or frost stat.
As I have already told you, If the frost stat operates it supplies T1 (SL) with voltage. This is connected to the zone valve micro switches and pump!!

Is your Worcester "Engineer" employed by them or a WAI ??
5 visits to site with no diagnosis.....He wants fookin knobbing !!!
You could prove if frost stat is faulty by temporary removing the feed from PL. Boiler would work normally but without frost protection.