Boiler comes on randomly

[philly55]

HI Folks
We had a new boiler fitted just over two years ago (Icos HE24) which has been great. Recently we had problems with the controller (a Donfoss FP715) screen going blank - having to switch off the power to restore the controller was a pain and (with help from this forum) replaced the controller a couple of weeks ago with a new one. All happy!
Except this last week the boiler has started up at strange times on its own, some times in the middle of the night, other times in the day. The controller shows both hot water and heating is switched off, yet the boiler is still firing up. Is this something to do with the controller change or is this a separate issue altogether?
Cheers
Phil

 

[45yearsagasman]

I'd be looking at motorised valves being faulty(end switches) and signalling the boiler to fire.

 

[philly55]

Yes, there's one. Is it something I can test or is it engineer time? I can use a multi-meter.
Cheers
Phil

 

[D_Hailsham]

Yes, there's one. Is it something I can test or is it engineer time? I can use a multi-meter.

If you have only one motorized valve, it will be a mid-position type and you have a Y Plan system.

How a mid-position valve works contains detailed fault-finding instructions.