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Back boiler cuts out after 1 minute and radiators don't heat up

Discussion in 'Plumbing and Central Heating' started by SK10291, 14 Sep 2021.

  1. SK10291

    SK10291

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    Hi. I have an old back boiler. The system has an F&E tank and a Grundfos pump.
    This week I turned on the heating for the first time of the winter and the boiler turns on but cuts out quickly. The pipe nearby gets hot, but none of the radiators do.
    Around 5 years ago, a Fernox Total Filter 1 was added.
    I checked the F&E tank and it was filthy with orange-brown gunge, and the connection to the feed pipe looked like it was blocked. So I cleaned out the tank with a wet vac. But the system still didn't seem to fill and the radiators still don't heat up.
    I get the impression that the boiler is ok and there is either not enough water in the system or there is a blockage of dirt/airlock - something to do with poor circulation. The pipework around the pump, magnetic filter and boiler gets hot, but the radiators don't.
    I have checked the Grundfos pump turns easily with a screwdriver, and have tried it on all three speeds. It makes a gurgling sound and gets very hot.
    I have bled all the rads, pump and emptied and bled the TF1. Not much air comes out and, until I cleaned out the F&E, not much water either.
    A theory is that when I cleaned the tank, I didn't cover the feed pipe because it looked blocked and the tank was full of water, so maybe some of the dirty water got into the system but then got blocked further down as it was dirty water, hence the rads initially seeming to have more water but then the heating still not working
    I am reluctant to call a plumber until I've given up. I would be extremely grateful for any ideas.

    Mine include: 1) emptying the system and seeing if it refills 2) adding water via the air vent of the TF1 3) poking something into the feed pipe to try and unblock it 4) adding chemicals to the feed pipe to try and unblock it
     
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  3. terryplumb

    terryplumb

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    Is the pump actually spinning ?
    Do all radiators release water from their bleed valves or just hiss /air ?
     
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  4. SK10291

    SK10291

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    Before cleaning F&E they released nothing
    Now they release water (some a trickle, others spray it) but no hissing anywhere
     
  5. terryplumb

    terryplumb

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    Ok ,water is getting into the system. Is the pump actually spinning when c/ heating is on ?
     
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  6. SK10291

    SK10291

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    How do you tell? I feel a vibration but there's loud swirling of air or water too
     
  7. terryplumb

    terryplumb

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    What did you use to bleed the pump ,large chrome screw in the middle of housing ? You should get a trickle of water from it once air is expelled. Removing the chrome screw gives sight of the shaft which should be spinning ( have a large cloth to hand to catch water ,and don't allow water to get onto any electrics/ cable)
     
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  8. SK10291

    SK10291

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    Right. I removed the screw with the system off - didn't get any hissing or trickle of water but the screw and pump felt wet. Shall I try with the pump running?
     
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  10. terryplumb

    terryplumb

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    You can ,but it sounds like there isn't any water in the pump,but will at least tell us if pump spins.
    Did you try to rotate the shaft with a screwdriver ???
     
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  11. SK10291

    SK10291

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    Ok I just opened the bleed screw while running. No water came out and I can see the thing is spinning fast. Does this confirm we are short on water? Further, I just tried opening that valve on the dead pipe there and no air came out. can I fill the system through that? Thanks for your help [​IMG]
     
  12. terryplumb

    terryplumb

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    Yes your short of water. That vertical pipe is a vent ,to release trapped air.
     
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  13. SK10291

    SK10291

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    Ok. Is getting the feed pipe changed the only sensible route? What about filling the system myself via the air vent shown - is it unheard of to have it not be an auto-refilling system until next time I have a plumber out for something? Or trying to unblock it with a snake or chemicals?
     
  14. terryplumb

    terryplumb

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    Not really
     
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  15. SK10291

    SK10291

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