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Discuss no hot water, radiators ok in the Plumbing Forum area at

  1. ploppers

    ploppers New Member


    Over the past few days we've noticed that we have no hot water any more. It isn't cold, but it certainly isn't's barely warm, tbh.

    To describe our 'system':
    We have a gas boiler in the kitchen that heats water for both central heating (which still works) and for the hot taps. It fires up on demand, but doesn't seem to have any kind of 'tank' on it.
    We have a big tank in the airing cupboard that has an immersion heater (not sure how/when that works, but I guess we would have to turn it on manually).
    In the kitchen we have a timer that is set to switch on the boiler for hot water between 06:30 and 08:30 (it also has a separate timer for the radiators).

    The way I imagine it working is that the gas boiler heats water and fills the tank in the airing cupboard. I imagine there's a thermostat in there somewhere to tell the boiler when to stop, but I can't see it. I guess there's a closed circuit between the boiler and the tank, that the boiler heats up. I'm not sure what happens if we use up all the hot water in the tank while the boiler is switched on, but perhaps there's a valve so the boiler takes fresh water from the mains, or perhaps it continues to try to heat the water in the tank in a circuit, with the tank being filled from the mains(?).

    Anyway, something's not working, and I don't understand the system well enough to figure out what might be wrong and how to fix it. It does kind of seem like it's just a thermostat problem, and if it is in the airing cupboard with the tank then it is possible it might have been knocked when clothes/etc are put in there. It might also be possible that some pump isn't working - ie if the water isn't being pumped through the boiler and tank. If there's no flow, then I'm sure the boiler wouldn't turn on for safety reasons. ...but I'm just guessing.

    Any ideas?
  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    When you turn just the heating on does the boiler fire / light??
  3. ploppers

    ploppers New Member

    I don't know how to just turn it on, but if we increase the central heating thermostat to something high, then it turns on, yes. It takes several seconds (15?) as it always has, but then it makes a noise, and a couple of seconds later an led light to say the burner is on.
  4. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    TBH it might be best to employ a heating engy to check the system over and maybe service the boiler
  5. ploppers

    ploppers New Member

    One thing I tried a few moments ago, is to turn the hw timer to on all the time (perhaps that is what you meant). I didn't hear the boiler fire up or see the led light up, but the water does seem to be somewhat hotter than it has been, though not as hot as before this problem started. I wonder if the immersion heater is switching on instead of the boiler (wild guess).

    Even though we now have some hot water, I still feel like something is wrong. Why isn't it hot in the morning, after 2 hours of being 'on' (the timer is set for 06:30 to 08:30)?
  6. ploppers

    ploppers New Member

    I did as you suggest and called someone. He said turn everything on constantly for a couple of days. His theory being that a valve on the tank had stuck and having both systems on constantly might free it up.
    Thanks for the help.
  7. richard978

    richard978 Member

    Could be tank thermostat or three port but you would need to get a multi-meter on the wiring centre to determine which one.
  8. ploppers

    ploppers New Member

    Yes, he seemed to be asking me questions about such things. It seems my tank doesn't have a thermostat (or at least it isn't located where I thought from his description, and isn't anywhere obvious). He seemed to be suggesting a valve. I don't think I have a 3-port one, but perhaps do have two separate ones attached to a t-junction which feeds into a pump. I'm making a lot of assumptions based on what they look like...there are 3 such things, but one is slightly bigger and looks more like a pump, while the other two seem to be more like valves. They all have power fed to them.

    The water does seem to be up to temperature since I turned it on all the time. It's been a while so I'll probably put it on a schedule again, perhaps a little earlier then before.
  9. ploppers

    ploppers New Member

    OK, so the water is tepid again :/ So, I'm again looking for a solution. I'd quite like to understand how the system works. I hope someone here can explain it. I don't think this house is so old, so it should be quite a 'recent' design (well, one can hope).

    I took some photos, in case it would help:

    The orange thing is what I thought was a pump rather than a valve, and oddly, Google Goggles identified it as a Grundfos UPS pump, and not cheap either, though there seem to be some sizeable discounts available. It has a setting on the side which was set to 'II' and I see from the diagram on the label that it represents a power (W) or pressure?. I did turn it to 'III' because I thought it was a thermostat, but I've turned it back to 'II' again.

    No sign of a thermostat.

    Can anyone explain?
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