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发布日期:2021年11月27日
Another Worcester Bosch Expansion Vessel failure question

Discussion in 'Plumbers' Talk' started by fizzy2, Jan 2, 2021 at 9:40 AM.

  1. fizzy2

    fizzy2 New Member

    I read some advice on this forum (thanks everyone) and checked my expansion vessel faults to find something that I think may be worthy of comment / question please?

    I have a bungalow with a 15 year old WB 28i junior with the pressure fluctuating (0-3.5 bar). I put a pressure gauge on the Schrader, water squirted out and it read the same as the system pressure (failed). I drained the vessel but realised it was difficult for me to change it (behind rear panel). So, I re-filled the system to 1 bar and re-checked the vessel pressure (also 1 bar). Tapping the vessel, I think it's now half full of water / half air and it appears to be working perfectly well (1-1.25 bar) albeit with a failed vessel. It appears that the vessel became full of air when I emptied it and became compressed to half full of air when the system pressurised to 1 bar above ATM (P x V = 2P x 1/2V). Why does the EV need the balloon (other than long term corrosion)?

    Why isn't this a similar principle to using a temporary empty radiator?

    Sorry if this question has already been answered!
     
    Last edited: Jan 2, 2021 at 9:46 AM
  2. quasar9

    quasar9 Active Member

    You should pressurise the air side to 1 bar with no pressure on the water side ( ie drained) otherwise the reading is not correct. Then pressurise the water side again to 1 or 1.5 bar. The rubber membrane usually perishes with age and perforates allowing water into the air side. Pressure higher that about 3 usually ends with PRV lifting
     
  3. fizzy2

    fizzy2 New Member

    Thanks for explaining but In the nicest possible way - I realise all that thanks. I'm not sure if you've read my post properly. The EV has failed, so pumping it up would not work if there's a hole in the rubber. Just allowing it to fill with air after draining it and failing to pump it up successfully seems to have fixed the issue and make the EV half full of air after letting the water back in at 1 bar.

    I'm asking...
    Why does the EV need the balloon (other than long term corrosion)?
    Why isn't this a similar principle to using a temporary empty radiator?
     
    Last edited: Jan 2, 2021 at 11:45 AM
  4. Severntrent

    Severntrent Screwfix Select

    Because of what has happened i.e. the air in the ev will gradually be absorbed into the water and will stop functioning correctly and corrosion as you have already stated. It is the same as a temporary fix with a rad, temporary being the operative word.As an aside large pumping mains sometimes require evs on them to stop the pressure in the main fluctuating to much, these vessels don't have membranes but may be of several m3 capacity made with 15mm + thick steel and require to be tested and certified every so often
     
    Last edited: Jan 2, 2021 at 11:59 AM
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  5. fizzy2

    fizzy2 New Member

    Many thanks. To be honest, the system was still working until I bled the radiators after the boiler service last month! It's only after bleeding them that the fault caused the pressure swings. I'd assumed that the air had become distributed around the system and was still compressible. In view of the fact that I have a one month old service certificate to sell my house in a few months, I'm wondering if I can gamble on not fixing it? I.e; morals aside here - does temporary last 2 months?
     
  6. quasar9

    quasar9 Active Member

    Sorry was in a rush, If you don’t fix it now, the PRV can lift and not resit properly again. Then you would have to replace the PRV too, not a quick job on a WB boiler.
     
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    #6
  7. Severntrent

    Severntrent Screwfix Select

    As long as you have enough air in the system to be compressed temporary canbe as long as you want, pick a radiator you don't really need, isolate it, drain it and put it back in service without bleeding it and keep a check on system pressure when heating is running.
     
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