Boiler coming on when it should be off

keith969

Recently I've noticed that the boiler comes on for about 30 seconds every 5 minutes or so, when the programmer is set for CH and HW off. Don't think its a problem with the programmer as the boiler still comes on turning the programmer to OFF.

The boiler is a Baxi System 100 HE Plus and the programmer is an Iflo. The system is pressurised unvented.

Anything I should check before getting the plumber to look at it?

Dusty_Bin_3

Could be the frost stat kicking in if the temperature drops below a certain point. This is to stop the system freezing up in very cold conditions.
I'm know expert, but as my boiler and frost stat are in the loft, mine has kicked in quite a lot during the night over the winter.

creased-leach

I was about to post exactly the same thing- we had people out to look at ours as it kept coming on in the night. Make a mental note of the temperature it happens at and go from there.

keith969

Actually don't have a frost stat on this installation, it does seem to be a problem with the boiler. Reading the instruction manual, it says that following a shutdown due to the boiler thermostat, timer or other heating control there is a delay of 3 mins before re-lighting. So it might be that it thinks its permanently on, and is just cutting out due to the thermostat?

gas4you

Could be a zone valve head stuck on telling the boiler that heat is wanted somewhere when it actually isn't.

keith969

gas4you wrote: »

Could be a zone valve head stuck on telling the boiler that heat is wanted somewhere when it actually isn't.

Would that still occur if the programmer is saying CH and HW should be off?

1984ReturnsForReal_2

Keith,

How long have you had the boiler?

How long have you lived there?

& have you ever had it serviced or any repairs? If so, what were the previous issues?

keith969

Moved in a few months ago, so have no idea... the boiler has been working fine up until now, and in fact still works, it just comes on when it shouldn't.

Think I will call the local plumber who I've been meaning to get in to service it!

1984ReturnsForReal_2

keith969 wrote: »

Moved in a few months ago, so have no idea... the boiler has been working fine up until now, and in fact still works, it just comes on when it shouldn't.

Think I will call the local plumber who I've been meaning to get in to service it!

Could it have been going on for a while & you not noticing it?

keith969

1984ReturnsForReal wrote: »

Could it have been going on for a while & you not noticing it?

No, pretty sure it only started happening in the last week as I can hear it coming on in the night - and didn't before.

keith969

gas4you wrote: »

Could be a zone valve head stuck on telling the boiler that heat is wanted somewhere when it actually isn't.

You were right... plumber found the zone valve on the CH side had a microswitch gone and that was telling the boiler to stay on all the time.