Unvented system losing pressure

Discussion in 'Plumbing and Central Heating' started by DiyCarr, 2 Mar 2021.

  1. DiyCarr

    DiyCarr

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    A687BF8B-C363-4992-A333-D7C6ECAFFFA7.jpeg 0279792D-6E75-4AE3-832E-E97E117FFD20.jpeg

    Hi all,

    looking for some suggestions to try and understand why my system is losing pressure.

    I have a system boiler serving an unvented hot water cylinder and central heating. Central heating circuit is set to 1 bar but drops to 0.8 every 1-2 days but doesn’t drop any further. central heating won’t kick in until I’ve refilled back to 1 bar. I’ve checked under the floor and the rads for leaks and can’t find any so struggling to understand where the pressure is going?

    Could it be boiler related or expansion vessel perhaps?

    I’ll undoubtedly call out a plumber, but I like to try and understand these things first.

    images of system attached
     
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  3. ianmcd

    ianmcd

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    which boiler do you have
     
  4. DiyCarr

    DiyCarr

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    93C10D32-4268-4CEC-A6C4-3D6291B423DB.jpeg It’s a Worcester Greenstar (not sure of model)
     
  5. Mike13

    Mike13

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    If there is air/hydrogen in the system it might go overpressure every time the heating kicks in, go round everywhere and bleed ALL the rads, then pressure again and see if it does the same?
     
  6. ianmcd

    ianmcd

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    You have a Greenstar Ri, when the system pressure drops to 0.8 Bar, do you get a flashing blue light on the boiler ?, try the cold pressure at 1.5Bar and see what happens, if you have an expansion problem you will be getting visible drops of water in the tundish, try placing a small piece of tissue across the diameter of the tundish and see if it gets wet , boiler shouldnt cut out at 0.8 Bar (your boiler doesnt have a low water content switch) it senses the way the heat is transferred from the boiler
     
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  8. DiyCarr

    DiyCarr

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    Thanks, I’ll give it a try. When pressure is at 0.8, the boiler fires up but then cuts out after a min or two. I can hear gurgling coming from the pump but the rads don’t heat up. The boiler keeps firing up every few mins (green light comes on) but the. cuts out again.
     
  9. DiyCarr

    DiyCarr

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    thanks, I’ll give this a try. I know I have one double rad where only one panel gets hot. I’ve tried bleeding it but it must be blocked as no air comes out. Could this be causing the issue?
     
  10. Mike13

    Mike13

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    well any air/gas in the rad will expand a lot from cold to hot, it will try and increase its volume and so raise the pressure, that can cause the overpressure valve to open, best get to the bottom of the problem with that rad before the plumber comes, if you can.
     
  11. DiyCarr

    DiyCarr

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    Makes sense! I’ll give it a go!
     
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