Boiler keeps running occassionally

[darianv]

Hi All,

I have a Vaillant boiler. Its managed/controlled by a Honeywell CM67 unit.
I have a set program for the heating to come on/off, and the tempratures that it should regulate at the programmed times.
Over the last 2 weeks occassionally the boiler keeps running and the heating doesn't turn off!
This is not the case everytime the boiler/heating turns on.
The flame indicator will come on the Honeywell unit, the boiler kicks in and heats up to the temprature, however the flame indicator goes off and the boiler keeps running!
I have to turn the boiler off, and keep it off for about 20mins and turn it back on. If i turn it on sooner it continues running too!

Any ideas why/what may be causing this?
Can I do repair this myself (i am not a boiler expert, but can get my hands dirty with some DIY!)

Thanks in advance,
darian

 

[ChrisR]

First thing I'd try is to take the CM67 off the wall while the boiler's on.
Lift the flap on the CM67 and you'll see an obvious place to put your finger nail, to get the battery compt out. IGNORE IT! There's a long slot lower right which works without breaking anything!
Then there's a small screw.

That should confirm it's the boiler. Note that the pump might stay on after the boiler flames have gone off but I expect you'd notice which it is.

After that - no idea. Would guess PCB but call Vaillant first. WHICH Vaillant is it?

 

[darianv]

Hi Chris,

To be clear the heating occasionally keeps running without turning off!
The house just gets hotter and hotter!
I hope that clears any confusion!

On the Honeywell, I have seen a clip on the right that can slide out to the right. It looks like there should be a watch battery of sorts in there, but there is nothing but grooves!
You metion a screw that would identify that if the issue is the boiler, but what should i do to the screw?

Not quite sure what model of Vaillant it is, as i cannot find a model no on the inside or outside of the unit doors.

Tks