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Discuss No DHW from combi boiler in the Central Heating Forum area at UKPlumbersForums.co.uk.

  1. marcuspreedy

    marcuspreedy New Member


    I am having to replace the unvented hot water system in my property, and as a temporary measure to get DWH downstairs I have un-isolated the supply from my Grant combi boiler.

    But, no hot water is forthcoming! I think it may be a problem with the Danfoss set3e programmer which a builder removed and replaced during renovation works.

    I have attached a photo of the wiring, and it looks to me if there should be a wire going into terminal 1 (Water-On) but which wire?

    Hope someone is able to help!

  2. Rob Foster

    Rob Foster Top Contributor!!

    Oh dear, If your not qulified you really must not be in there .
    Get an Engineer in .

    Shaun ..

  3. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    tbh your best guess is same as ours depends whats connected at the other end could be grey but who knows

    best get a pro in to check what the builder has done / disconnected
    • Like Like x 1
  4. townfanjon

    townfanjon Trusted Plumber GSR Top Contributor!!

    A combi should come on as soon as you open a tap, so no idea why theres all that lot in there
  5. CBW1982

    CBW1982 Plumber GSR Top Contributor!!

    That just looks like CH wiring. Looking at the diagram there’s no wires for dhw. As TFJ has said it’s a combi, so open a tap, should get dhw, if you’re not then employ a GSR who can work on boilers.

  6. SimonG

    SimonG Trusted Plumber

    For a grant then he will need a good oil engineer.
    • Informative Informative x 1
  7. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    oil combi needs a two chanel prog for the store etc
    • Informative Informative x 1
  8. marcuspreedy

    marcuspreedy New Member

    Thanks for your suggestions so far, I managed to do a bit more investigation and have come up with the following wiring plan.

    The DHW switched live from the boiler appears to go to the HTG com on the programmer, which doesn't seem right to me.

    It's an oil combi! No requirement for Engineer to be GSR.

  9. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    what about perm live and neutral also earth?
  10. marcuspreedy

    marcuspreedy New Member

    I've left them out for clarity !
  11. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    if your drawning is correct which im not sure is

    brown should be in 1
  12. marcuspreedy

    marcuspreedy New Member

    The drawing is correct.

    I agree it would make sense that brown (from boiler) should go to 1.

    I'm going to try that now!
  13. Stu-B

    Stu-B Active Member

    If the brown is supposed to be in no1 then surely at the moment it would make the DHW be permanently switched on as it’s connected to the looped permanent live.
    But you say you’re not getting any hot water. Where is the grey wire connected at the other end?
  14. marcuspreedy

    marcuspreedy New Member

    The Grey wire is not connected at either end.
  15. marcuspreedy

    marcuspreedy New Member


    I have now put the brown wire (SL-DHW) into terminal 1.

    The water from the tap is no-longer at incoming temp of 8°C, but only reaches 24°C briefly and then falls away!
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