Central Heating comes on when only Hot water is on

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We had British Gas out for an annual Boiler Service last week. Since then we have noticed that even though we dont have the central heating on (via timer / control panel in the airing cupboard) the radiators are heating up whenever the timer is on for hot water only - even though the thermostat is at 5c. If I switch only the heating on the radiators do not come on until I increase the thermostat as you would expect.

Obviously not what we want when trying to save on gas usage currently and it still being mild. I have booked British Gas to come back out but the earliest appointment is not for another two weeks (I am seeing if they can bring it forward as issue only occurred after their last visit).

I suspect its something to do with the 3 way switch in the airing cupboard and we had something similar many years ago and it was replaced. But I seem to remember it was constantly clicking back then.

I know there are some savvy folk on here so wondering if there is anything obvious I can try whilst waiting for BG engineer to come back?

Thanks
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Comments

  • QrizB
    QrizB Posts: 13,822 Forumite
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    It does sound like a stuck or faulty three-way valve.
    Some (not all) three--way valves have a lever on the side that you can use to move them from one setting to another. Does yours?
    N. Hampshire, he/him. Octopus Go elec & Tracker gas / Shell BB / Lyca mobi. Ripple Kirk Hill member.
    2.72kWp PV facing SSW installed Jan 2012. 11 x 247w panels, 3.6kw inverter. 30MWh generated, long-term average 2.6 Os.
    Taking a break, hope to be back eventually.
    Ofgem cap table, Ofgem cap explainer. Economy 7 cap explainer. Gas vs E7 vs peak elec heating costs.
  • P1Fanatic
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    I wondered if heating would come on if both heating and water set to On but thermostat set low and it does. As if so I could set heating schedule same as hot water. Unfortunately it still comes on when Hot Water is on.
  • P1Fanatic
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    QrizB said:
    It does sound like a stuck or faulty three-way valve.
    Some (not all) three--way valves have a lever on the side that you can use to move them from one setting to another. Does yours?
    Yes its a danfoss unit and has a metal lever on the left. Up is auto and down is manual (its always been left in Auto mode). I'm not sure what manual mode means (in terms of HW / CH / HW+CH). Trying to find some user docs online.
  • P1Fanatic
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    Its a Danfoss HSA3:

    https://store.danfoss.com/en/Climate-Solutions-for-heating/Motorised-Zone-Valves/3-Port-Motorised-Valves/Valve-Actuators-3-Way/Zone-Valves,-HSA3,-Mid-Position,-Supply-voltage-[V]-AC:-230,-SPST-(interlinked)/p/087N6587

    Their docs seem to be all about installation / wiring / specs etc not actual operation. From what I read elsewhere manual mode is if your heating is not working you can set to manual. I have the opposite issue in that my CH is coming on when only HW is set to On.
  • QrizB
    QrizB Posts: 13,822 Forumite
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    edited 9 November 2022 at 11:15AM
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    Does yours have the sticker with a pair of arrows on it, on the side of the housing? Something like this:
    Is there a little indicator that sticks out to show whether the valve is set to A, B or somewhere in the middle? (There might not be.)


    N. Hampshire, he/him. Octopus Go elec & Tracker gas / Shell BB / Lyca mobi. Ripple Kirk Hill member.
    2.72kWp PV facing SSW installed Jan 2012. 11 x 247w panels, 3.6kw inverter. 30MWh generated, long-term average 2.6 Os.
    Taking a break, hope to be back eventually.
    Ofgem cap table, Ofgem cap explainer. Economy 7 cap explainer. Gas vs E7 vs peak elec heating costs.
  • P1Fanatic
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    QrizB said:
    Does yours have the sticker with a pair of arrows on it, on the side of the housing? Something like this:
    Is there a little indicator that sticks out to show whether the valve is set to A, B or somewhere in the middle?


    Exactly like that with the white part facing outwards so the sticker is underneath (facing the floor). Metal lever is as per pic which is Auto mode which is where it should be. I've moved it down to midway (there is no marking there) normally its either Top=Auto or Bottom=Manual (where yuo can push lever back to lock it there).

    A/B on that sticker relates to exit pipes A = HW, B = CH and AB = HW&CH.
  • QrizB
    QrizB Posts: 13,822 Forumite
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    OK, I think I know of a way to stop the radiators getting warm but it's going to require a little bit of DIY work. (I had a similar problem with my 3-way valve a few years ago, but mine's a different model - I'm hoping they all work in a similar way.)
    • The actuator housing is attached to the valve body by two screws. Remove them.
    • Underneath the actuator you'll see the valve spindle. It has a flat on it. Place a small spanner on that flat (or, if you're very careful, a pair of pliers) and gently turn the valve to shut off flow to the radiators.
    Don't do any of this if you aren't comfortable.
    N. Hampshire, he/him. Octopus Go elec & Tracker gas / Shell BB / Lyca mobi. Ripple Kirk Hill member.
    2.72kWp PV facing SSW installed Jan 2012. 11 x 247w panels, 3.6kw inverter. 30MWh generated, long-term average 2.6 Os.
    Taking a break, hope to be back eventually.
    Ofgem cap table, Ofgem cap explainer. Economy 7 cap explainer. Gas vs E7 vs peak elec heating costs.
  • diystarter7
    diystarter7 Posts: 5,202 Forumite
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    Hi
    Just a quick one.
    Our combi/Valiant did that in the summer several years ago as i noted some of the rads were warm.
    It was something called the 'diverter'  - I  dont believe it cost more than 150 inc parts etc it may have been around a hundred quid.

    And the hot water at the time was not as hot as it was supposed to be.
  • Apodemus
    Apodemus Posts: 3,384 Forumite
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    QrizB said:
    OK, I think I know of a way to stop the radiators getting warm but it's going to require a little bit of DIY work. (I had a similar problem with my 3-way valve a few years ago, but mine's a different model - I'm hoping they all work in a similar way.)
    • The actuator housing is attached to the valve body by two screws. Remove them.
    • Underneath the actuator you'll see the valve spindle. It has a flat on it. Place a small spanner on that flat (or, if you're very careful, a pair of pliers) and gently turn the valve to shut off flow to the radiators.
    Don't do any of this if you aren't comfortable.
    Yes, I've done this in the past as a temporary fix.  But I would suggest that the OP should turn off the power before removing the actuator housing!
  • oldagetraveller1
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    This is exactly what was happening to my system in September.
    Same Danfoss three way valve and actuator.
    It was the actuator that was stuck and not quite at the end of it's travel for hot water only. The manual lever position indicated that.
    BG changed it after determining the actual valve wasn't sticking/stuck.
    That particular motor unit had only lasted 4 years.
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