I am responsible for a vacant house with a natural gas combi boiler (Ideal Logic range). I need to keep the house heated to a minimum temperature, but would like to switch off mains water (pipe freezing risk).

Will the boiler accept not having a mains supply for the heating closed circuit? I don't think it should need a mains supply, but software, etc. can be fussy.

I can and will simply try it out, but don't want to risk it cutting out while not at the property, or accidentally damaging the boiler.

  • 1
    Why is there a freezing risk if the house is kept at a minimum temperature? Why do you need to keep the house at a minimum temperature if you empty all the pipes (heating included). These two things are closely related, and you seem to be tying your hands by separating them.
    – jay613
    Commented Oct 17, 2023 at 9:44
  • Does the boiler have a low water cutoff switch?
    – jay613
    Commented Oct 17, 2023 at 9:45
  • 1
    @jay613 the minimum temperature is a condition of insurance (irrespective of the mains water. I don't know why, maybe bad drafting, but life's too short).
    – Dan
    Commented Oct 17, 2023 at 9:46
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    A heating-only boiler could be used without supply, with some cautions, but a combi boiler will be more model-dependent, and you should consult the manual and possibly the manufacturer's customer support. This question might help (but not very much). And note, that and other questions ask about plumbing a combi boiler with the DHW pipes capped. In your case they would not be capped, and may or may not contain water under unknown pressure.
    – jay613
    Commented Oct 17, 2023 at 15:32

1 Answer 1


Provided that the water pressure indicated on the boiler is within the manufacturer's specified range, a combi boiler can run indefinitely with no water supply. It keeps recirculating the same water round and round.

If the pressure gauge ever falls below the minimum, you would have to turn the water on again in order to re-pressurise the system.

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