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Thread: Evohome - comfortable temperature

  1. #21
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    The radiators sometimes get hot and sometimes don't put I haven't managed to pin down the pattern yet (i.e what was the boiler doing and what were other zones set to at the time).

    I think that probably rules out airlocks as that would stop them ever getting hot?

    Pressure is a pretty constant 1.5 but wouldn't budge any higher than that (I only mention that in case it suggests an issue?)

    The living room is definitely warming up as it's down around 15 overnight and then gets back to 18 but very rarely any higher (the occasional 18.5).

    Thanks again for all your suggestions.

  2. #22
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    Other thoughts - is the pump under-sized for the system or equally is the boiler under-sized, i.e. number of radiators @ various BTU ratings matching boiler output.
    If the boiler was under-sized and only running at 65C and the sitting room is 'at the end of the line', and it only gets to decent heat when you shut down balancing valve(s) on other rads, might that be a possible cause?
    Last edited by killa47; 20th December 2018 at 05:47 PM.

  3. #23
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    Have a feel of (or measure if you can) the temperature of the RETURN pipe just before it reaches the boiler. If the water is hotter than an apparently 'open valve' radiator then I think you have a problem.

  4. #24
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    Radiator balancing issues could certainly be the cause of the problem. I would try balancing all the radiators to see if it helps.

    The easiest way to do this is to get hold of a digital infrared temperature gun (approx 25 for a good one) that will show the surface temperature of the radiator panels. Open all lock-shield valves then let the system completely cool down over night (put it in heating off mode to disable your normal automatic morning warmup) then in the morning when you're ready set all zones to 25C so they all come on with 100% demand at once.

    Then repeatedly go around all the radiators measuring them with the IR gun to see which ones warm up first and which ones warm up last. You'll probably find your living room is one of the laggards and in fact it may not warm up at all while all the other radiators are fully open.

    Then try reducing the lock-shield valves on the ones that heat up first the most, the medium delay ones a little and the ones that are slow to warm up leave them fully open. Whichever radiator is the slowest to warm up should always have it's lock-shield valve left fully open.

    Then turn the system off and let it fully cool down again and repeat the test. You may find that you need to progressively tweak it over multiple sessions over a few days due to the long cool down period. To get it right it's a somewhat tedious and time consuming process. What you're aiming for is for all radiators to warm up at about the same rate during that initial warm up phase from a cold system with all zones suddenly turned up high. There shouldn't be any radiator that is well ahead of the rest or well behind the rest.
    Last edited by DBMandrake; 20th December 2018 at 08:53 PM.

  5. #25
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    I've checked the return temperature at the boiler and it's only luke warm to the touch.

    The boiler should be big enough. It's a Worcester Bosch greenstar 42cdi classic in a fairly standard 4 bed detached house with 12 radiators.

    I've turned the boiler up to 73ish with no noticeable improvement.

    Sounds like, given the return temperature, balancing might be my best option. Leaving the heating fully off overnight will be unpopular as we have guests over Christmas! Might be possible afterwards though.

    Thanks again for all the suggestions guys.

  6. #26
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    Keep in mind a return temperature that is about 20C lower than the outbound flow temperature is actually what you'd expect from a well balanced system.

    If it's even more than this though (as luke warm would seem to imply) it could suggest the pump speed is too low. What speed is it set to ?

  7. #27
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    As far as I can tell there is no pump speed setting. Pump speed might be the issue though as I've noticed the boiler seems to be cycling even when the rooms aren't up to temperature.

  8. #28
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    Quote Originally Posted by mjombly View Post
    As far as I can tell there is no pump speed setting. Pump speed might be the issue though as I've noticed the boiler seems to be cycling even when the rooms aren't up to temperature.
    I have a WB Greenstar 40CDI boiler, similar to yours, and used to have continual cycling issues. Eventually I arranged for WB to install a later version main PCB, which reputedly (per internet anecdotal forums)solved the cycling issue - and it did. It won't solve the specific low temperature problem for the sitting room rad, but if ever you want to fix the cycling issue, a new PCB is worth a try.

    On our system, the constant cycling was causing a regular drop in circulating heat but we have some 23 rads, 3 towel rails.

    If your pump is a Grundfos UPS 15 60 or similar, there should be a speed selector switch on the body with three flow settings - I, II and III.

  9. #29
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    Quote Originally Posted by mjombly View Post
    As far as I can tell there is no pump speed setting. Pump speed might be the issue though as I've noticed the boiler seems to be cycling even when the rooms aren't up to temperature.
    Depends what you mean by "cycling". If you mean the boiler is going over the set flow temperature and having to shut the burner off completely for a while then yes, pump speed being too slow may be an issue, as a low water flow rate will limit the amount of heat transfer possible. Or the boiler could be over spec'ed for the house and number of radiators, or the boiler may have a poor modulation ratio.

    Is the pump internal and part of the boiler itself ? I wonder if it's a modulating pump ? Even if you don't have a speed setting it may have a slope adjustment for the pump if it's a modulating pump. Are all your radiators on 15mm pipes or do you have older 8/10mm pipes ?

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