1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

New pump but boiler stops firing before room temperature is reached.

Discussion in 'Plumbing and Central Heating' started by SJRSJR, 19 Mar 2017.

  1. SJRSJR

    SJRSJR

    Joined:
    25 Nov 2006
    Messages:
    484
    Thanks Received:
    6
    Location:
    London
    Country:
    United Kingdom
    Hi. After the combi boiler pump failed I was feeling pleased with myself for flushing the CH system and changing the pump head (Grundfos UPS2 15 60). I would have liked to have changed the whole pump because the pipe was a bit cruddy but access to the nuts was difficult. Overall though the drained water was very clear so I didn't bother with any cleaning fluid, just inhibitor.

    It was a relief to have the heating on and get hot water again. However even with the room thermostat set to 30 the boiler switches itself off well before then (I can hear the thermostat dial 'clicking' at 20). It fires up again after a while but only for a few minutes before switching off. It's maintaining warm but not hot radiators. All have been bled and TRV valves are fully open. The radiator and hot water dials on the boiler are on max. I don't have a thermometer but the flow and return pipes are similarly warm to touch. The hot water is working okay. Does the pump drive HW and CH or just CH?

    Before changing the pump I hadn't noticed a firing up problem but I knew the radiators weren't getting hot and assumed it was all pump related.

    The boiler is a Halstead Finest Platinum (12 years old). I know it will need changing soon but I'm trying to eke it out through the summer. Any thoughts on the likely cause and what I can do to resolve it? Thanks.
     
  2. Sponsored Links
  3. Agile

    Agile

    Joined:
    26 Jun 2004
    Messages:
    63,979
    Thanks Received:
    4,583
    Location:
    London
    Country:
    United Kingdom
    I would love to make a suggestion but that is difficult without knowing what the flow temperature is.

    Ideally the temperature in degrees. But failing that a hand touch comment, like can only keep hand on top of radiator for two seconds.

    The pump operates for both CH and DHW.

    When was boiler last serviced?

    Tony
     
  4. SJRSJR

    SJRSJR

    Joined:
    25 Nov 2006
    Messages:
    484
    Thanks Received:
    6
    Location:
    London
    Country:
    United Kingdom
    It was last serviced three years ago (I know!). I can keep my hand on the pipes indefinitely, they're not too hot to touch.
     
  5. steve32

    steve32

    Joined:
    23 Nov 2008
    Messages:
    845
    Thanks Received:
    165
    Location:
    Essex
    Country:
    United Kingdom
    How did you flush the system with a flushing machine or chemicals and a hot flush
     
  6. SJRSJR

    SJRSJR

    Joined:
    25 Nov 2006
    Messages:
    484
    Thanks Received:
    6
    Location:
    London
    Country:
    United Kingdom
    I just emptied and refilled twice using the filling loop. I couldn't believe the water was so clear.
     
  7. SJRSJR

    SJRSJR

    Joined:
    25 Nov 2006
    Messages:
    484
    Thanks Received:
    6
    Location:
    London
    Country:
    United Kingdom
    I'd like to buy a thermometer to see what temperature the pipes are. Is any digital thermometer (as found in Boots or kitchenware departments) okay to use? Thanks.
     
  8. JohnD

    JohnD

    Joined:
    15 Nov 2005
    Messages:
    73,402
    Thanks Received:
    4,226
    Location:
    Crossgates, Europe
    Country:
    Cook Islands
    If you're lucky enough to have a good-quality multimeter, it may have a socket for a thermocouple. They are simple and fairly cheap.
     
  9. andytw

    andytw

    Joined:
    7 Feb 2012
    Messages:
    490
    Thanks Received:
    59
    Location:
    Somerset
    Country:
    United Kingdom
    I use a digital laser one. It was about £15 from screwfix. I believe it is quite accurate. Works a treat on white painted radiators.
     
  10. Sponsored Links
  11. D_Hailsham

    D_Hailsham

    Joined:
    18 Oct 2007
    Messages:
    10,587
    Thanks Received:
    1,343
    Location:
    Kent
    Country:
    United Kingdom
    But will be waaaay out if pointed at bare copper pipe. The trick is to wind some insulating tape round the pipe (any colour) and hold the IR gun close to the tape.
     
  12. therambler

    therambler

    Joined:
    21 Mar 2017
    Messages:
    10
    Thanks Received:
    1
    Country:
    United Kingdom
    How did you establish that the pump needed replacement? A symptom of a faulty pump is the boiler running until the water in it gets to the preset boiler stat temp and then shutting down. Without the pump running the water in the boiler is more or less dead-headed. The water in the boiler will heat up rapidly but the heat will only spread slowly through the water because there is no flow, so the rads will not reach working temp before the boiler cries enough and shuts down.

    It sounds like it may not have been the actual pump but maybe an electrical fault that caused the initial fault and is still there.
     
  13. SJRSJR

    SJRSJR

    Joined:
    25 Nov 2006
    Messages:
    484
    Thanks Received:
    6
    Location:
    London
    Country:
    United Kingdom
    Sorry, thought replies had run out on this one

    therambler - a plumber told me I needed a new pump. I could hear him bashing it which got a couple more weeks out of it but after that it stopped working altogether. After I put the new one in everything fired up again. If the hot water heats okay but the central heating doesn't reach its temperature, does that suggest any particular fault? Thanks
     
  14. oldbuffer

    oldbuffer

    Joined:
    6 May 2010
    Messages:
    1,393
    Thanks Received:
    523
    Location:
    London
    Country:
    United Kingdom
    If the hot water is OK, and the boiler fires up in the normal way, the problem is likely be one of poor circulation. The boiler fires, the flow side heats up, but the water can't circulate properly, the difference between flow and return temperatures at the boiler is outside the normal range and the boiler shuts down. Flow side cools and off it all goes again. Try and see what the difference in temperature is between the flow and return pipes, at the boiler, when the boiler shuts off.
     
  15. Agile

    Agile

    Joined:
    26 Jun 2004
    Messages:
    63,979
    Thanks Received:
    4,583
    Location:
    London
    Country:
    United Kingdom
    To give you proper advice we need to know the flow and return temperatures!

    Tony
     
  16. SJRSJR

    SJRSJR

    Joined:
    25 Nov 2006
    Messages:
    484
    Thanks Received:
    6
    Location:
    London
    Country:
    United Kingdom
    Thanks for the quick reply. Could you explain the theory of flow and return temperatures (it's a combi boiler)? What should I be looking for and is it anything to do with balancing the system? I've not been able to work out the order in radiators heating up.
     
  17. SJRSJR

    SJRSJR

    Joined:
    25 Nov 2006
    Messages:
    484
    Thanks Received:
    6
    Location:
    London
    Country:
    United Kingdom
    Ok, I haven't bought a thermometer yet. At the risk of ridicule the flow pipe is 'quite hot but not scalding' and the return pipe is 'warmish'!
     
Loading...

Share This Page