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Discuss Worcester 28Si II, system bar pressure going very high. in the Central Heating Forum area at

  1. JasonM

    JasonM New Member

    I would be very grateful if someone can give me some advice on the following.

    I have a Worcester 28Si II combi boiler in the house where I live, the hot water side is working fine, however I have an issue on the radiator heading side.

    When the heating is on the bar pressure is going very high, I have filled the system so the bar pressure reads 1 bar at cold, however once the heating is activated the bar pressure is eventually going past 3 bar, at this point I turn the heating off. I have also noticed at this point the relief valve is activated as water is coming from the pressure relief pipe on outside of house, I assume with the high pressure building in the system.

    To try and remedy I have checked the air pressure on the car tire type valve on the expansion vessel. The valve was checked by pushing the center pin and only air came out (no water vapor). A car tire pump was used on the valve to attempt to re-pressure the expansion vessel, however I'm not sure what pressure should be used for the expansion vessel, I have been told it should be 0.5 bar however to me this seams quite low. After pressuring the expansion vessel the same issue with system pressure going high still exists.

    Could someone please confirm what bar pressure the expansion vessel should be pressurised to?

    Also is there anything else I can check to what could be wrong.

    Also if it helps, I first noticed the issue when the heating went off, when I checked the boiler the bar pressure was showing 0 (needle was resting on stop), and with a flashing light on boiler. This appeared to happen quick as if something had suddenly failed to cause the issue.

    Many thanks for you help.
  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Common issue tbh and the only fix as your not qualified is to get a gas safe engy out maybe worth a service if you haven't had it done in a few years
    • Agree Agree x 1
  3. JasonM

    JasonM New Member

    Hi ShaunCorbs, there has been a gas safe engineer out to the issue, boiler serviced also, however I really wanted to confirm the bar pressure for the expansion vessel. The reason I ask is he said 0.5 bar, however he did a call to ask someone the pressure when I was present and I was sure I heard 1.5 said over the phone, i'm just trying to make 100% sure on what the pressure should be on the expansion vessel.
  4. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    1.5 bar would be the heating system pressure and expansion vessel have to be set in a certain procedure
    • Agree Agree x 1
  5. Harvest Fields

    Harvest Fields Trusted Plumber GSR Top Contributor!!

    If you have a set of your boiler instructions take a quick look in there.
  6. Chalked

    Chalked Plumber GSR

    Without going into detail. Different expansion vessels and systems need different pressures. .
    I'm afraid you/ engineer are doing it completely wrong. You can't compress water.
    I would get a different qualified gsr .
    • Agree Agree x 1
  7. Harvest Fields

    Harvest Fields Trusted Plumber GSR Top Contributor!!

    I agree, you wouldn't want 1.5 bar in your expansion vessel.
    • Funny Funny x 1
  8. JasonM

    JasonM New Member

    Thanks for everyone's response, this is what happened.

    The engineer came out and pressed the pin on the expansion vessel valve, I was told no water is coming out, just a tiny amount of air.

    He then tried to pressurize the system with a 12v electric car pump, however he had to guess the pressure as he no pressure guide with him (really he had no pressure gauge) .

    He is going to try and pressure the system again on Monday, however he says if this does not work it will require a new expansion vessel, also more money as the boiler has to be removed from the wall to get access to lift the expansion vessel out.

    What should the procedure be, i'm worried something will be done wrong and I replace the expansion vessel when I don't need to.

    Many thanks again
  9. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    :D I guess he didn't drain the system
    • Agree Agree x 1
  10. Harvest Fields

    Harvest Fields Trusted Plumber GSR Top Contributor!!

    If you are unsure of his capabilities as an engineer. I would say get another engineer in.;)
  11. JasonM

    JasonM New Member

    Should the system be drained to solve this then?

    What is the procedure that should be done?
  12. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    The best advice is to get an experienced engineer in
    • Agree Agree x 2
  13. jtsplumbing

    jtsplumbing Plumber GSR

    Please note that its not always the expansion tank that causes this problem, so don't just replace it, until the other common fault has been checked, service engineer should know what to look for and will be less than a new tank.
    • Useful Useful x 1
  14. JasonM

    JasonM New Member

    Just an update on this and people’s thoughts, it’s actually quite interesting what’s gone on, please read till the end.

    So just to summarise the original fault. There was an issue with bar pressure in the system once the radiators got up to temperature, this was causing the pressure release valve to open and vent heated water outside.

    So initially a gas safe engineer serviced my boiler, he attempted to re-pressurise the expansion vessel by pumping air into the valve at top of boiler. The pressure was taken to 0.5 bar however it made no difference and the problem still occurred. He also blead the radiators at this point, however there was no air in them.

    He said the only option to fix the issue was a new expansion vessel, however it’s probably going to be expensive as to remove the old expansion vessel the boiler would probably need removing from the wall (the boiler is in a garage and ¾ up a wall). He said the cost would probably be around £400 as it’s maybe a days labour alone if the boiler is removed. So I asked if that guaranteed the issue would be solved and was left with a blank face. It’s also worth mentioning this chap had been back to my house 3 times, the second time to service a gas fire, and the last time to quickly check some radiators that were not heating up. Turns out one radiator was shut down, and other may have an issue with a value, that radiator has always been slow since I’ve owned this house.

    Not wanting to carry out the above work to boiler without any guarantee it would be resolved I had had a second gas safe engineer look at boiler. This is the part it gets interesting.

    The second gas safe engineer serviced the boiler again, he then checked the expansion valve and said because no water is coming out it’s a good sign. He attempted to pump up the expansion vessel, however unlike the first engineer he lowered a pipe from below boiler and he extracted water from the expansion vessel into a bowl using this pipe. He said there is a lot of water inside the expansion vessel, he also said as no air is coming out so the expansion vessel does not need replacing. The amount of water BTW was almost 2 kitchen sink bowls up. He said the water had been building up for a while, I asked if there was anything wrong with boiler and he said no and this is something that’s done with normal servicing. To cut to the chase, the issues is resolved. I’ve been in this house 4 years and never had the radiators this good before.

    Also worth mentioning, the first engineer never checked my boiler for emissions. The second engineer had a machine to test gas the system was outputting. I had a quick look at government regulations and as far as I can tell gas emissions should always be checked.

    My thoughts on the above.

    Why did the first engineer not attempt to drain the expansion vessel, I’m really dump founded why this could of happened. From everything I can gather this is a common issue on this boiler and he should have known about. Worse if I had not trusted my instinct I would have had a bill for so many hundreds for work that was not required.

    Can anyone please give me there view on all of the above.
    Many thanks
  15. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    :D do the first engy tried to pump the expansion vessel up with it still connected lol

    And you are supposed to connect the flue test machine to the boiler on a service
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