Combi Boiler query

TheBanker Posts: 1,912 Forumite
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A question for those who are more knowledgeable... I have a Combi Boiler and although I intend to cut back, it will be running during the winter to heat the house.

If I need hot water, e.g. to wash up or clean something, is it more cost effective to do this at a time of day when the heating's on? Logically I think it should be because the boiler's already running and hot.

Thoughts and intricate calculations welcome!

NB: I do realise that any potential saving is likely to only be a few pence a month. 


  • TimSynths
    TimSynths Posts: 603 Forumite
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    I'm going to say yes, with mine the water is hotter and comes quicker from the tap when the heating is going.
  • macman
    macman Posts: 53,098 Forumite
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    With a combi, you can't run both at once anyway. When you turn the hot tap on, the heating is switched from the CH circuit to the DHW side. if you ran the DHW continuously, the rads would eventually go cold.
    The two are different circuits. The DHW is heating cold water coming off the rising main, the CH is reheating water on a sealed flow and return loop.
    No free lunch, and no free laptop ;)
  • Vincero
    Vincero Posts: 67 Forumite
    First Post
    It should end up being a little bit quicker as the heat is already built up / soaked in to the boilers heat exchanger and the heating water loop which cycles through it.

    Temperature stability may be a little compromised if there is a wide disparity between your heating temperature and water temperature settings - if the hot water temperature overshoots then the boiler will modulate it's output down (or off) and then start building up again as needed.
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