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CH not switching on until HW switch activated?

Discussion in 'Plumbing and Central Heating' started by chipcutter, 2 Dec 2015.

  1. chipcutter

    chipcutter

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    I had a new Grundfos UPS2 15 50/60 pump fitted in April this year by a local heating engineer as the other one seized and blew fuses.

    Two weeks ago we switched CH on (through wall timer programmer in airing cupboard) which controls water and central heating. The Grundfos fails to switch on when calling for CH only, however if you wait for HW to come on or manually press HW to ON the Grundfos CH pump comes on too. A local service engineer had a look and replaced the actuator head only (Drayton) but it still waits for the HW to activate.

    Before the new Grundfos was fitted CH had no problem coming on at separate times as did HW (twice daily). We get hot water and rads are OK - just this.

    A the moment HW and CH come on at exactly the same time in the morning so everything functions as normal. HW goes off at 10am and CH at 11am. CH comes on at 2pm but does not activate Grundfos pump? If I manually activate the HW button the Grundfos switches on and I can immediately press off for HW and the pump will still keep going?

    The Grundfos if showing three green lights with the middle one glowing the brightest - I thought only one should be ON to indicate speed?

    So, Grundfos pump will not come on unless HW is running; it will however continue running if the HW switches off.

    I am NOT an engineer and will NOT attempt fiddling with pipes and electrics, but I would like to understand what may be the fault before spending more money on something so annoying!

    Thanks
     
  2. stem

    stem

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    You don't mention how the boiler is effected. Does this fail to come on in central heating only mode also?

    The following description relates to a 'Y Plan' with a three port motorised valve. [An 'S Plan' with two, two port valves is slightly different]

    When hot water is 'on' the hot water cylinder thermostat turns on the boiler and pump. So far so good. But, when central heating only is required, the motorised valve winds to the central heating only position and inside the motorised valve is a small microswitch that operates the boiler and pump now that the hot water cylinder thermostat is not doing so.

    If the microswitch has failed, or the wiring between it and the boiler / pump is faulty, neither the pump or the boiler will operate when central heating only is selected.

    Changing the head of the valve should have rectified a faulty microswitch. If it has never worked properly since the pump replacement, it may be that the pump has been incorrectly wired in. The only way to check what is actually happening is with electrical test equipment.
     
    Last edited: 2 Dec 2015
  3. chipcutter

    chipcutter

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    Thanks for that STEM. The CH, once fired up by triggering the HW, will continue as normal and the boiler reacts to demand from the temperature of the heating. Just to clarify again, the CH heating works fine on its own without HW being on, but it needs the HW button pressed to trigger the pump. As soon as this kicks in (about 1 second) you can switch HW OFF and CH continues as normal!

    So the CH demand from the programmer/timer is failing to independently activate the Grundfos pump.

    Am I right in thinking it may be an electrical fault? My son is an electrician so I could at least get him to check out the circuits.
     
  4. stem

    stem

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    If your son is an electrician that's great. Here is a link explaining how it should all work, he can select the different systems (Y Plan or S Plan) and their various conditions which will show what should be live and when.

    http://octaveblue.co.uk/c_heating/index.htm
     
  5. chipcutter

    chipcutter

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    I am very grateful for that STEM, I will get him to check it out and let you know how we get on and what we find.

    It may be a couple of days, but whatever, I will let you know.

    Again, many thanks.
     
  6. chipcutter

    chipcutter

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    Well Stem, I said I would get back to you, well here it is... very positive result - yippee!! Thanks for your insistence that the electrics should be checked - valuable lesson.

    Like most families if there is something you want done by a family member (my son) you are usually the last person to get it. However, things were really getting bad with the heating so my son came round on Tuesday and went through the electric circuits. CH had been very intermittent and only coming on, to some degree, when water was called for as well, except that it totally failed on Tuesday!!
    After one and a half hours of diagnostics he had found TWO faults - one was quite surprising; the pump. We have never heard or felt the Grundfos pump working although the little LED would come on when engaged with the hot water being switched on. Fault 1 - The pump was in fact FAULTY; it has only been in use for about 7 weeks since we switched it on in late November. All that could be heard was a little dull tick every 2 seconds and we think it was only rotating, if at all, very slowly.
    Fault 2 - The other main fault was the programmer on the wall, a relay had failed on the CH side although the LED came on as normal. My son realised this and simulated it by making two conections on the separate box assembly that joins all the wires together into one box (the one with all the long row of connector points); it had something to do with the white cable, however, to cut a long story short he got a new programmer box and a new pump in case. He fitted the programmer and immediately ALL functions were re-instated. We changed the pump and immediately realised that the old (but new last year) one was obviously faulty. You can quietly hear the latest one happily turning at speed and gently feel the vibration of its movement.. result happiness!
    Not very happy with the original fitter that fitted the duff one as he couldn't have checked it very well, he could have cost me a fortune trying different things. Just shows how important electricians are and how some problems can be found purely through electric diagnostics... lessons learned.
    We have subsequently found out that there was a bad batch of Grunfos pumps of this type last year - looks like we were unlucky.
    EVERYTHING works now as normal. Thanks again.
     
  7. stem

    stem

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    Glad it all worked out in the end, and well done to your son with the troubleshooting. Sometimes it is impossible to solve problems such as this via a forum and physical testing and inspection is the only way.
     
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