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Discuss Worcester Bosch Greenstar 28i LOSING PRESSURE in the Central Heating Forum area at

  1. Ahmed

    Ahmed New Member

    Hello. This is my first ever post. My boiler is just over 5 years old and started losing pressure a few days ago (daily drop of approx 0.5 bar). A Gas Safe Engineer carried out a full service. EV needed to be re pressurised and he said that all was well. A few hours later pressure dropped again.Called him. Followeing his advice was :
    1. PRV - tied a bag over to see if there was any water collected. None
    2. Condenser pip was bone dry.
    3. No obvious radiator leaks or towel rail leaks. (7 rads + 2 towel rails)
    4. No Air lock in the system - I bled all the rads
    5. No visible leaks in or around the boiler.
    6. Isolated the boiler (and switched it off) for 24 hours to see if the pressure dropped. IT HAD (1.5 to 1.0bar)
    Can someone please explain where the water might be going?
  2. Craig Watson

    Craig Watson Plumber GSR Top Contributor!!

    Isolating the boiler unfortunately isn't fool proof as you won't know if the valves have fully shut off. Your only option is to call your engineer back and get him to check the boiler and the system over.
  3. Ahmed

    Ahmed New Member

    The engineer is on holidays. If the valves ARE fully shut off, what could be causing the pressure drop?
  4. bogrodder

    bogrodder Plumber GSR

    You have probably got a leak on the pipework, be it under the floorboards or in the walls or buried in concrete.
  5. Rob Foster

    Rob Foster Top Contributor!!

    0.5 bar in 24 hrs is about 2.00 to 3.00 litre on a system of your size. Than ought to display itself if its in a ceiling void or a stud wall but might well go undetected in underfloor pipework. Its also too much for radiator stabbings. It will take some detective work, I would make sure the boiler isolating valves are really fully closed and then go for it...push the pressure right up go round look and Listen and be ready with a drain hose in case it really goes lala. I have wide experience in pressurised domestic heating system failure. Rob Foster aka centralheatking
    You isolated the boiler and the pressure dropped ...but how do you measure the pressure, on the boiler gauge itself I expect. So is the pressure drop occuring in the boiler while isolated or on the rest of the system when you open the valves.
    Last edited: Apr 11, 2019
  6. Ahmed

    Ahmed New Member

    Rob, here are the answers to your questions 1) isolating valves fully closed 2) pressure drop of 0.5 bar is with the valves closed and and electric power to boiler turned off 3) a further small drop when I open isolating valves and turn elec power on.
  7. Rob Foster

    Rob Foster Top Contributor!!

    So the boiler is loosing 0.5 bar not the heating system ? A drop of 0.5 bar within the boiler will be very small volume of water but I would expect to see it.
  8. Ahmed

    Ahmed New Member

    Wow..Many thanks for the speedy response. I am not a pro. (infact quite dumb really). With the the boiler isolated, does the guage measure the pressure of boiler or the entire system+boiler?
  9. Rob Foster

    Rob Foster Top Contributor!!

    if the gauge is on the boiler then it measures the pressure at the boiler, so isolate the boiler as you have done then this is the pressure in the boiler alone. centralheatking...I am off out shortly till 13.00
  10. Brambles

    Brambles New Member

    Am I reading you correctly:

    The boiler is under pressure, has been switched off for 24 hours and you have isolated the boiler at both flow and return boiler isolation valves?

    The boiler has lost at least 0.5 bar over the last 12 hours. ie the pressures have both been recorded whilst the boiler is cold.

    You cannot see any signs of leakage around the boiler or the prv

    You are satisfied that the expansion vessel is properly charged with an intact bladder

    If all the above are correct, and the boiler isolation valves are not passing, then you probably have a leak inside the heat exchanger.

    You will need a GSR engineer to investigate this.
    • Like Like x 1
  11. Ahmed

    Ahmed New Member

    Many thanks for all your help guys. Brambles; all your assumptions are correct. As the full service was carried out only 3-4 days ago, should the GSR engineer not have noticed the leak in the heat exchanger?
    • Like Like x 1
  12. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    Again Brambles please be wary of information you are giving relating to components inside the boiler.

    To the OP you are saying that the boiler loses pressure over a number of hours unless you are willing to pay you cannot expect the engineer to stand there and wait for a drop that may not happen
    • Like Like x 1
  13. Brambles

    Brambles New Member

    First prove that the boiler isolation valves are not passing. Switch the boiler off let system cool adjust system pressure to 1bar close both isolation valves depressurise the system on the heating side. Monitor boiler pressure it should be static at around 1bar . loosen each isolation valve on the heating side for 5 secs then retighten- catch all the water!

    If the boiler pressure is static at 1bar the valves are probably ok.

    If you are satisfied that the expansion provision is ok ( as you said the GSR confirmed it was), then call the GSR man back.

    Generally, if the heat exchanger is leaking it is hard to get good combustion analysis readings.
  14. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    How much did you pay for the service ?
    • Agree Agree x 1
  15. Ahmed

    Ahmed New Member

    I paid £85. The engineer said it was for the "full strip-down service". I believe he meant a comprehensive service. He did change a few gaskets/washers etc, use the meters to do the gas seal test, carbon dioxide test and so on
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