We moved house a few months ago and our property either has the same or a very similar boiler to our old house. It's a condensing boiler, a Worcester Greenstar 37cdi and the controls look identical. However, it has an odd behaviour that our old one didn't: it turns itself on, very briefly, at intervals through the night.

Nothing actually comes on. The fire-up only lasts maybe twenty seconds and the radiators don't heat up. It's the middle of summer so the thermostat is turned right down. I think - but I'm not certain - that it does this at fairly consistent times.

The trouble is that where the boiler is positioned underneath two of the bedrooms it sometimes wakes people up with the noise. We'd really like to stop it, especially since the fact our old boiler didn't do it suggests it's some kind of setting.

However, I can't figure out what it might be. Trying to troubleshoot it on google isn't helpful as you get a lot of answers from people whose boilers are coming on full blast during the night, which isn't our problem at all.

Does anyone have any suggestions as to what this might be or what I could try to change to stop it from happening, short of turning the boiler off all night every night?

  • Perhaps you had a time control on the old boiler that turned it off from 11pm to 6am - does the new one have that and is it set correctly? If not, fit one - most heating controllers do that afaik...
    – Solar Mike
    Jul 20, 2021 at 9:16
  • @SolarMike We had the old one fitted while we lived there and I'm not aware we had such a control. The engineer fitted a wireless thermostat which the new one also has, although the thermostat is completely different. Could that be the source of the problem, potentially?
    – Bob Tway
    Jul 20, 2021 at 9:24
  • 1
    Does the boiler also provide domestic hot water? And do you have recirc plumbing? If so, it may be popping on every once in a while to keep the hot water pipes hot. ...just a thought. Jul 20, 2021 at 12:43
  • Does the boiler have a dedicated circuit breaker or "light switch"? If so then I would turn it off during the summer until you have time to troubleshoot it or call in a professional.
    – MonkeyZeus
    Jul 20, 2021 at 14:11

1 Answer 1


The boiler has a couple of functions that might explain this:

Preheat keeps a supply of hot water in the boiler at all times. It reduces waiting time when used for hot water supply. The manual explains how to turn that on and off. This could be the cause, even if you're not using it for hot water. Heat loss would cause a cycle of regular heating as you've observed.

Antifrost senses and fights near freezing temps in the boiler. Less likely but if wired incorrectly or if the antifrost sensor is bad this could be the cause.

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