CH Possible Fault

Discussion in 'Plumbers' Talk' started by Cambar, May 16, 2018.

  1. Cambar

    Cambar New Member

    Hi all, has any one any ideas what might be causing the following

    We have a water tank with a normal gas boiler which is gravity fed, with a three way valve operating to split water to the radiators.

    The tops of the radiators are getting hot when the central heating is turned off.

    Reading online everything points to a faulty three way port but I’ve just discovered the boiler temp is set to 80 degrees but the tank stat at 60 degrees.

    Is it possible the stored water has been getting too hot and then sent to the radiators or is there anything else other than the three way valve that is causing it.

    The whole system is less than 3 years old.
  2. I presume the rad tops become warm when the CH is off but the DHW is on? In which case, it would seem like a wee bit of letting by, and the 3-porter is the most obvious culprit.

    Having the boiler set at 80oC is sensible as it would take this level of heat to get the hot cylinder up to its required 60oC quickly. Imagine if the cylinder was fed by a 60oC flow? Would it ever get to 60oC when you take in to account heat losses?! It would certainly take an age. So that's all good.

    Ok, a few wee tests:

    1) With the system ideally cool, ensure the programmer is set to 'off' for both DHW and CH and then turn the whole system's power off at the isolating switch for 10 seconds. Get someone to turn the power back on while you monitor the pump and 3-port valve - basically nothing should happen.

    Ok, now turn the prog to 'on' for the DHW only. The valve shouldn't respond, but you should notice the pump has fired up and the central pipe to the 3-port valve becomes hot pretty quickly. Check the temps of the two outlet pipes from the valve by placing your fingers on them at least a foot away from the valve body; you should notice that the DHW outlet (the one heading to the cylinder side) becomes as hot as the inlet pipe - too hot to touch - within a half-minute or so. You should similarly notice that the CH pipe does not get hotter hardly at all. If it does, it would suggest that your valve is faulty.

    Report back :)
    exbg likes this.
  3. Cambar

    Cambar New Member

    Apologies for the late reply. Everything happens exactly like you said so looks like it’s definitely the 3 port. Cheapest rubbish available has been fitted too which is good to see ha.
  4. So the CH outlet from the 3-porter IS becoming a bit hot when the programmer is only calling for DHW?
  5. Cambar

    Cambar New Member

    Yes it gets warm straight away, CH not as hot as the DHW but definitely warming from cold when there should be no CH activity.
  6. That would seem pretty conclusive then :oops:

    Assuming that the plumbing hasn't been joined up in some weird way.

    Easy DIY job, with the only tricky bit being having to drain the system to below the valve's height. I suspect that most valves (play safe - go for a Honeywell) will be a straight swap. Very good chance you can even reuse the existing nuts and olives if pulling the old ones off doesn't float your boat.

    (When you remove the old valve, try one of the new nuts on it - if it goes on without issue, job's a goodie.)
  7. Peterdevon

    Peterdevon Active Member

    Is there a bypass? and is there a valve on the hw circuit restricting the flow in anyway?

Share This Page