CH blockage or slow pump?

Discussion in 'Engineers' Talk' started by RedToby, Mar 22, 2023.

  1. RedToby

    RedToby New Member

    Hi folks,

    Had conflicting advice about the cause of a partial central heating failure. Worried that there still seems to be no solution in sight and wondering what else to try. Bit of a long one ahead!

    System is an Ideal Logic combi boiler which runs first to 4 radiators upstairs and then down to another 4 radiators downstairs. Radiators of various ages (a couple due for replacement soon) but whole system has been running all year without a single problem.

    Had an upstairs radiator moved and some nearby pipes renewed. Next day, downstairs radiators are stone cold.

    Try the basics: bleed radiators, top up pressure in the system. No change.

    Original plumber comes out, notices and fixes small leak where upstairs radiator was reattached. Apologises and bleeds what is a large amount of air. Says it is likely there is a stubborn airlock elsewere in the system or a need to rebalance. Advises that I try rebalancing system, bleed radiators again and make sure it stays at optimum pressure and see what happens.

    I do this and- progress- hall radiator (which is pretty new) downstairs is now getting warm at top (others still cold). TRV-side pipe to radiator nice and hot but lockshield side almost no heat at all.

    Try manually flushing hall radiator. Water comes out absolutely clear and no change to situation once I reattach. I call out a heating engineer.

    He looks at both radiators, new radiators and boiler and says they all appear to be fine. Says that rebalancing was a mistake (?) because insufficient hot water will be circulating to the downstairs. Says likely cause is a blockage in one of the older radiators. Opens all the lockshields wide, sends off for system cleaner and advises a colleague will be round in a few days. Says a power flush will be necessary to clear blockage if doesn't work.

    While I wait, notice the only change is that pipe leading to hall radiator is no longer getting hot.

    Heating engineer two comes round, tries the cleaner (no change yet), inspects system and says problem isn't acting like a blockage. Says he thinks the boiler's pump isn't working properly and sends off for a replacement. Waiting for that now.

    Not sure what to try if that doesn't work. Reluctant to spend money I don't really have on a powerflush if it's not clear that the cause is a physical blockage. It would be easy to spend hundreds on this without fixing the problem. I'd have thought the leak or new pipework on the original radiator would be the cause but I've now had two opinions otherwise.

    Is there anything else I can try to fix the problem or at least get a firmer idea of the cause?
     
    Ben John likes this.
  2. Mike83

    Mike83 Screwfix Select

    Are the isolation valves on the boiler fully open? Check that first.
     
  3. Bob Rathbone

    Bob Rathbone Screwfix Select

    How old is the pump in the boiler. The capacitor in the pump motor ages after about 15 to 20 years and the pump speed drops, the capacitor should be checked but the CH eng will not know how to do that, only change the pump.
     
  4. RedToby

    RedToby New Member

    Thanks both

    Just had a look- yes they are

    Whole boiler is about 10 years old, pump is no older than that. Relaxed about the pump being changed if the insurance covers that, but is it still worth getting the capacitor specifically checked if not?
     
    Last edited: Mar 22, 2023
  5. Mike83

    Mike83 Screwfix Select

    Is there a bypass on the system somewhere?
    Does the return pipe back into the boiler get hotter than all the radiators?
     
  6. RedToby

    RedToby New Member

    Aside from the automatic bypass on the boiler, I haven't seen a bypass anywhere on the system (assume this would be a visible valve? maybe exposing the limits of my knowledge here :D )

    Return to the boiler was warm when I last looked- certainly a similar temp to the working radiators but I'll check more carefully
     
  7. Mike83

    Mike83 Screwfix Select

    If the return at the boiler is hotter than the radiators this means the water is bypassing the radiators.
    This will cause issues with them heating up.
    This can be caused by a bypass valve or if the system is incorrectly piped.
    If the return is the same temperature or slightly less than the radiators then the issue lies elsewhere.
     
    RedToby likes this.
  8. Bob Rathbone

    Bob Rathbone Screwfix Select

    If you are changing the pump and it costs you noting, don't worry about the capacitor, scrap the pump.
     
    RedToby likes this.
  9. RedToby

    RedToby New Member

    CH engineer looked at both possibilities for me and diagnosed it as incorrectly joined pipework (I still got the new pump first, a bonus at least).

    Just need to get remedial work on the pipes done and all should work. I'm so relieved to know what the problem is. Thanks both for your help
     
  10. Ben John

    Ben John New Member

    it seems that the pump may not be working properly, which could be the root cause of the issue. If replacing the pump doesn't solve the problem, it's worth considering whether the new pipework or radiator move may have caused any issues with the system. If the problem started after these changes were made, it's possible that something was not reconnected or installed properly. A professional inspection of the new installation may be necessary. Overall, systematically troubleshooting the system and ruling out potential causes is the best way to identify and fix the problem.
     

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