Boiler running for DHW when not called

[Rockingit]

I generally consider myself pretty up on heating systems but this has me slightly stumped… An otherwise very simple system boiler on what I assume is an bog standard S plan. What could make it call for DHW (tank stat registering cold after a full draw) OUTSIDE of the programmed hours and having ascertained that there’s no call from the timer? Turn the main iso off and on again and it stops.

 

[littlespark]

Looks like a faulty programmer.
Can you swap it out temporarily to prove?

Or someone’s messed up the wiring

 

[plugsandsparks]

Could have a zone valve stuck in open position, had it just the other day, client was saying "how do i stop the boiler coming on", lol

 

[Rockingit]

Could have a zone valve stuck in open position, had it just the other day, client was saying "how do i stop the boiler coming on", lol

Yeah, that’s my thinking also (2 port) although wouldn’t explain why it then stops after a power cycle