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Thread: combis and hot water

  1. #1
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    Default combis and hot water

    It says that when using a combi boiler you have hot water on demand and that it takes precedence over CH.

    However, when the room thermostat clicks in the CH, the pump starts to circulate the CH water but does not immediately fire up the boiler - consequently the water in the heat exchanger cools down. If you now turn on the hot tap, the boiler will fire up, but the water from the tap remains at the same temperature as that in the exchanger i.e. cool or, if you catch it at the wrong moment, cold.

    Should it do this?

    Thanks for any advice.

  2. #2
    Moderator sunbeam's Avatar
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    initialy you will always get a slug of cool or cold water at the taps unless you have a combi with a heat store faciliy,

    what make of boiler is it?

  3. #3
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    sunbeam

    Thanks for your reply.

    The boiler is a Grant Combi 90 Outdoor Module MarkII.

    I can understand that I might get cool or cold water initially, but if I leave the tap running it does not heat up at all, although the boiler is firing.

    Any further thoughts appreciated.

  4. #4
    Moderator sunbeam's Avatar
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    if you can get to them try turning of the boiler isolators that feed the central heating usually sited on the pipes directly under the boiler there will be two of them on two 22 mm pipes,

    then turn on the hot water if it gets hot now, then the diverter valve on the boiler is passing through to central heating, when on hot water.

    what i mean to say is when you are calling for hot water the hot water in the boiler is getting diverted round the central heating instead.

  5. #5
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    Thanks. The problem is that I have had 7 different installers, mechanics and technicians look at it and change virtually everything on the boiler including the diverter valve, heat exchanger, thermostat etc etc and while most say there is definitely something wrong, the Grant people say this feature of not getting hot water when the HC is calling for heat is one of the features of combi boilers! (not according to the manual!).

    I shall try: turning on the hot tap - make sure it continues to run cool/cold - make sure the boiler is firing and see if the CH continues to get hotter. This will then confirm that the hot water is not taking precedence over the CH.

    I shall report back!

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