This may be confusing and long, sorry. I have a combi boiler, a couple of years old. It was serviced a few months ago. I have a separate freestanding thermostat. I keep it on manual so I can switch the heating on as and when I want it (having it on auto or a timer etc wouldn’t be useful as me and DP work odd shifts, I air rooms out at random times and it would be a pain changing the times every day to suit)
For the past few weeks I’ve noticed the radiators hot when I know I haven’t switched the heating on. As far as I can see they aren’t on for long before I notice it (based on Octopus half hourly readings). It’s also at random times in the day/night, as far as I can tell it happens only once in a day, but not every day.
It also used happen last year in spring. This was after we used the timer when we had more consistent shifts. After we stopped using the timer programme, and kept it on manual it started coming on randomly. When it happened last year, I played around with the thermostat and in the end the only thing that seemed to stop it was putting it on auto and putting required temp extremely low, below 10 degrees so the heating wouldn’t kick in, as it was toward the end of spring we knew we wouldn’t need the heating at all.
For the life of me I can’t find the manual, its been shoved somewhere during major refurbs but I remember the manual saying the heating would switch on if the temp falls below 5 degrees to avoid the pipes freezing. But the temp has never got to that level.
A side note - I think the thermostat may be showing the incorrect room temperature as it is, as at times it will say 13 degrees but I don’t feel that cold (I’m very cold usually, below 18 to me is freezing). I’ll be getting a room thermometer to compare but haven’t had time recently
When it was happening last year, I got in touch with the installer but he couldn’t find an issue. Because it obviously doesn’t happen consistently I can’t ‘show’ him what is happening, and it probably sounded like user error. I also can’t be sure that it has only happened at the times I’ve noticed it, whether it is happening more than once a day. It may well have been happening throughout summer but I spent most evenings in the garden when at home. and likely wouldn’t have noticed.
Could it be some sort of boiler self maintenance thing? Or some sort of comms issue between the boiler and the thermostat? I could leave it on to see whether it switches itself off after a certain time, but cost would be a concern.
Luckily so far it hasn’t cost us much, but I am forever paranoid that one day I’ll get home and the heating will have been on for 12 hours!