Glow Worm Ultracom CXI unexpectedly starting

Good morning and a Happy New year to everyone.

I've a question about a Glow worm Ultracom CXI combi-boiler that keeps starting up. It's at my mum's house so details a bit sketchy but here goes....

C/H is set to come on at 06:30 - 09:00 then 15:00 - 22:00 and that's been fine up to a few days ago.
Got a call late last night that the boiler is still on at 23:45 and the rads are really hot. Thermostat was set to 22 degrees. As far as I can tell remotely by what my mum has said the system hasn't been set to override the set times. She was concerned enough that I just told her to turn it off from the wall switch. Turned it on this morning and still happening.

Seems this boiler has a frost protection system(?) but would that cause this behaviour? We are in SE England and temperatures have been around 0 degrees for the past couple of days & nights. Mum moved to the property last January and I don't remember the boiler doing this then (I did a quick check of temps Jan & Feb 2020 and doesn't look as though we had an extended period of cold weather then.

Boiler was serviced in November this year.

Thanks in advance.

Mark

The boiler frost protection should cut off once flow temp reaches 35oC. Is there another frost stat on the system? Is there a programmable stat or timer that has been overidden? Is there any zoning on the system controlled by motorised valves?

oilhead said:

The boiler frost protection should cut off once flow temp reaches 35oC. Is there another frost stat on the system? Is there a programmable stat or timer that has been overidden? Is there any zoning on the system controlled by motorised valves?

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Hi and thanks the the reply.
I'm going round there later so will check those things. The most obvious is maybe the system has been set to override but mum says it still comes on when thermostat is turned down to 15 degrees. It's a small 3 bedroom bungalow so hoping it's a fairly simple set-up (from what I'd seen of it).

If the heating is on with the thermostat turned down go into D.8 on the control panel, if it says 1 you have an external control problem, with the room thermostat turned down it should say 0

ianmcd said:

If the heating is on with the thermostat turned down go into D.8 on the control panel, if it says 1 you have an external control problem, with the room thermostat turned down it should say 0

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I've got the user manual but not the installation one. Is there an easy way to get into the diagnostic menu?

FYI the boiler was showing pressure of 2.8bar which I think is a bit high so I've drained off some water from a few rads to get it to 2.0bar so I'll monitor that - top-up water inlets both set to OFF position.

Also it wasn't set to override the timers.

Update.

Overnight and this morning no random boiler start-ups reported so fingers crossed it's sorted. Don't see the relation between the high(?) bar pressure and the boiler going rogue, something to bear in mind I guess.

Thanks for the replies and a Happy New Year to everyone.