Worcester heatslave 15/19 won't stop firing?

[Fat Bob]

Never seen this problem before. It is a worcester heatslave 15/19 fitted with a Bentone burner. Boiler is around 15 years old.

The red light on the control box is on, like the boiler is locked out, but the burner is still firing.

I have the hot water and central heating turned off at the programmer, and both the central heating and hot water thermostats on the boiler turned right down.

I have had to leave the boiler off, because it is dangerous. I can't phone worcester, because it is a Sunday and their office is shut.

Has anyone got any ideas? Thank you.

 

[oilhead]

Does it still have the post purge unit ? This can put power back down to the box. Has anything been changed? EBI? Solenoid coil? Motor? If some component has shorted out, it can have fused a relay on the PCB. If burner is still running with lock out lit then that has fused contacts and will need replacing.

 

[Fat Bob]

Does it still have the post purge unit ? This can put power back down to the box. Has anything been changed? EBI? Solenoid coil? Motor? If some component has shorted out, it can have fused a relay on the PCB. If burner is still running with lock out lit then that has fused contacts and will need replacing.

Do you mean the PCB? I tried the control box on the burner, I had one in the van, but had the same problem.

 

[Terrywookfit]

Have you checked the flow switch.

 

[Fat Bob]

Have you checked the flow switch.

No. I will try disconnecting that tomorrow and see if that stops it.

I just can't understand why the lockout button on the control box is lit, and the burner is still firing.

 

[oilhead]

Have you checked the flow switch.

Good call if the control box fault wasn't there. If a new control box has the same fault, without getting the meter out, it's hard to diagnose, especially as the stats are turned right down. Can't remember now if flow switch by passes the timer.

 

[Fat Bob]

Good call if the control box fault wasn't there. If a new control box has the same fault, without getting the meter out, it's hard to diagnose, especially as the stats are turned right down. Can't remember now if flow switch by passes the timer.

The control box is brand new. Tried it out a few days ago when I thought it was the likely cause of a temperamental burner. It worked fine then with no red light on it.

Could the back box on the control box be the reason why the lockout is lit, but the burner still firing.

 

[oilhead]

Like I said, time to get the meter out. You've not said whether the boiler has a post purge unit.

 

[Fat Bob]

Like I said, time to get the meter out. You've not said whether the boiler has a post purge unit.

Yes it does have a post purge unit. I phoned worcester and after a few of them had a discussion about this unusual fault they said I should replace the post purge unit. When I asked why, their reply was it is cheaper than the PCB, so should replace the cheaper part first.

I tried linking out the post purge unit, and the boiler would not fire at all. Worcester had been told this, but still thought it could be the post purge unit.

Anyway I still felt it had to be the PCB, so I replaced it and it is now working like normal. Thanks for all your help.