Secondary pump on combi boiler heating circuit?

Discussion in 'Plumbers' Talk' started by Alethea, Nov 4, 2021.

  1. Alethea

    Alethea New Member

    We have a newish heating system, with a Worcester green star 28i compact (I think), with two twin pipe loops. The flow and return come out of the boiler, then have a t into two separate loops. The loop that is straight on has 4 big antique radiators, and runs them all fine. The loop that comes off the t has a longish run of pipe and then two radiators. I can’t get the heat to go into this second loop, except when we cracked a valve and drain water from near a radiator to pull it through, when the heat did come that far, but stopped once we reconnected it. There’s no air in it that we can find. We are racking our brains and can’t figure it out. Can I add a pump to the return on this second loop? If so what do I wire it into?
    Any help appreciated, normally I can balance radiators etc, but this has stumped me.
    Thanks Alethea
  2. Bob Rathbone

    Bob Rathbone Screwfix Select

    Their will be air trapped somewhere in the pipes, you could fit a secondary pump which will only be needed to push the air out of the pipes then disconnect it. I would close the valves on the big radiators on loop 1 and turn the pump up to full speed and see if the radiators on loop 2 start to get warm. When all is working correctly, turn the pump back down and open the raditor valves on loop 1.
    Kingscurate likes this.
  3. Alethea

    Alethea New Member

    Thanks for that advice - sounds like it’s definitely worth a go. Am I assuming this is better on the flow, to push the air into a radiator and be able to bleed it out, rather than on the return to push it into the boiler? Really appreciate your knowledge on this :)
  4. terrymac

    terrymac Screwfix Select

    Throttle down the lockshields on all the rads that are heating up. The system isn't balanced.
  5. heatyman

    heatyman Well-Known Member

    Water is lazy and takes the easy path. You get heat after cracking a valve because you've lessened the resistance on the long circuit. Turn the low resistance antique rads down to match the resistance of the other loop.
    Just a thought, what load do the antique rads total? Does it exceed the boiler output?

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