Central heating won't turn off

[mogget]

Do you have a multimeter, and the knowledge of how to use it and stay safe when working on electrics?

 

[BigBadBarry]

Thanks. Just found another box (see edit to my last post). Looks electrical to me - no pipes.

 

[BigBadBarry]

Do you have a multimeter, and the knowledge of how to use it and stay safe when working on electrics?

Yes. I have a meter and know a reasonable amount about electrics. Not too sure of working with mains voltages, but I know the principles. Do you have an idea?

Sorry - I need to go out now, but will check back on here later/in the morning for any updates.

 

[mogget]

That's the main junction box - if you know what you are doing you could check that there is no voltage between brown and blue wires of the myson valve when heating turned off (with system powered up). If there is 230v then there is a problem with the controls.

Then, if there is no voltage, isolate the system, disconnect orange and grey wires of myson valve, check for continuity between them. If there is continuity then the microswitch is closed and the valve is stuck open.

EDIT: We crossed posts there.

 

[BigBadBarry]

Thankfully my system seems to be working normally again. I think the stuck valve theory is a good one - seems to have got unstuck again!

Thanks to everyone who took the trouble to help. I'll post back if problems resurface but for now, it's all OK.

Great forum.