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Discuss Lukewarm 'hot' water - secondary heat exchanger already changed in the Central Heating Forum area at UKPlumbersForums.co.uk.

  1. Gazzzz101

    Gazzzz101 New Member

    It is the flow sensor, the boiler is going into preheat and not max burn.
     
  2. Gazzzz101

    Gazzzz101 New Member

    Sorry, just read the thread again.
     
    • Funny Funny x 3
  3. Darren Jackson

    Darren Jackson Plumber GSR

    As #townfanjon says, you should not get any water flowing at all from the hot taps or shower ect.. if you have isolated the cold feed to the boiler! If you do there is a crossover somewhere in the pipework. Most likley a mixer valve, mixer tap or a mixer shower that is letting cold water into the hot supply cooling the hot down at the outlets. If you have iso's fitted to your pipes under the taps, then turn off all the cold ones leaving the hot ones on. Then turn the supply back on to the boiler and see if you now get hot at the outlets. Also check that you have double check valves fitted to all the mixer taps and showers if not get some fitted. If you do get hot coming through then one at a time turn back on a cold iso to a tap then try the hot again if it stays hot you can rule that tap or shower out and it is ok. If it runs Luke warm again then leave that particular one isolated and move on to the next tap and repeat untill you have tried them all. Hopefully this will identify the crossover. If that still does not work then there is a pipework problem and someone has inadvertently piped a cold supply to your hot pipe! That will need to be found and rectified but that may involve pulling up floor boards and taking off the covers to any boxed in pipes to trace the pipework and hopefully find the problem.
     
    • Like Like x 1
  4. Neil Sutherland

    Neil Sutherland New Member

    Thank you. I shall persevere and let members know what I find. I'm gradually resigning myself to having to pull up the bathroom floor to trace the pipework, but will try to pin it down a bit further before I do that!
     
  5. Neil Sutherland

    Neil Sutherland New Member

    Progress report. Turns out isolating valves are fitted to the bath mixer taps in both bathrooms, but not to either of the showers. So I've ruled out the bath mixers, but still have suspicions about the shower mixers. These are Grohe Avensys exposed thermostatic valves (34 029) and I note from the installation manual that they have internal non-return valves. I'm thinking of replacing those (though at £18 a pair it would be cheaper just to fit check valves in the supply pipes). Worth a try before lifting floors? Also, I'm having to replace the valve mechanism in one of the showers (over £100) because it drips constantly. I wonder if that is exacerbating the problem?
     
  6. Neil Sutherland

    Neil Sutherland New Member

    And I'm wondering now whether I should fit flow restrictors to the shower inlets - but that seems to require measuring the hold and cold pressures which I'm not equipped to do. I always assumed the pressures were similar as the hot water is essentially under mains pressure when a combination boiler is used?
     
  7. diptin dogshi..

    diptin dogshi.. New Member

    An isolating valve is not a double check valve? Did you do as suggested and turn off the cold isolator then see if the tap ran hot or did you mistake isolating valves for one way valves and eliminate them on that basis? Confused reading your progress update sorry
     
  8. Neil Sutherland

    Neil Sutherland New Member

    Sorry if I wasn't clear! There are no isolating valves on the shower supply pipes (hot or cold) so I wasn't able to isolate them. More news at the weekend, I hope!
     
  9. diptin dogshi..

    diptin dogshi.. New Member

    Very confusing thread this...
    Must be my eyes o_O
     
  10. Vee

    Vee Plumber GSR

    Sounds like the thermistors need replacing. Had exactly this on that type of boiler.
     
  11. Neil Sutherland

    Neil Sutherland New Member

    Success - at least partially. When I stripped down the Grohe shower valves I found that one was missing the non-return valves in the elbows. I've fitted new valves and, while I was at it, fitted flow restrictors on the cold side. I now have hot water at the taps and even the showers are tolerably warm. I suspect there may yet be more to find, but I'm feeling a lot happier - as is the rest of the family! Thanks to everyone who's chipped in to this thread.