Plumbing Help Needed – Combi Boiler DHW not working!

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  • Plumbing Help Needed – Combi Boiler DHW not working!
  • All was well until I bled a rad the other night. Now we get CH as per programmed but no hot water on demand. Had a look in the boiler (getting quite familiar with it now!) and the actuator comes out of the 3 way diverter and presses the microswitch, but the boiler doesn’t fire up. If the heating is on at the time, the boiler just goes out ans stays out, and then doesn’t come back on for the heating.

    I took the DHW microswitch and activated it manually and it fired up – got the missus to then turn a hot tap on and the boiler went out!

    Any ideas what’s going on?


    (its an Ideal (!) c80ff if it helps)

    Central heating boiler pressure too low? Not 100% familiar with the different types of boilers but if the rads are a closed system you may have a filling loop you can connect to put the pressure back into the recommended zone on the gauge.

    Edit: Sorry, miss read the post and thought you had hot water and no heating…


    Any ideas what’s going on?

    No, sorry…..

    Last time I had heating but no DHW it was the diaphram, apperantly common on my baxi potterton HE30.

    If it fires by manually pushing the micro switch, it’s not that. Could be the diaphragm is failing and not moving enough, or low system pressure. Fill it up to 2 bar first

    Filled it up to 1.5 bar – still not working; would this affect DHW?

    Yes, if the pressure is too low, the diaphragm won’t move properly on most boilers. 1.5 should be enough, but take it up to 2 to be sure.

    Are you sure the diverter pin is moving far enough out?


    quadruple check that the radiator isn’t leaking…? this happened with our combi and eventually I found one rad had a slight seep.

    A diaphragm is usually around 35 quid, most plumbers will just swap the full diverter valve, 120 plus

    The diverter pin is defo coming out plenty – had an issue with it seizing in the past, so been lubing it up – there is a slight leak out of the aperture come to think of it, could this be the source?

    Also, the rad in question seems to need bleeding every 2 months or so.

    How old is the boiler? Do any other rads require bleeding?

    just under 10 years old. Nope – just that rad (upstairs, boiler is in loft)

    Tall towel rad?

    Does seem a bit odd.

    Does your boiler ever need refilling due to high pressure discharge?

    I’m thinking possibly a weak valve on the filing loop, coupled with a dodgy micro switch.

    Try swapping both, you’ll get a micro switch cheap on ebay, or try parts center/plumb center

    During December it did randomly suffer high pressure and discharged through the relief valve/pipe, but been ok before and since.

    Just a normal rad.

    Heating just stop working, but turning boiler off and on for a bit got it going again. weird.

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