Worcester Bosch Boiler Pressure Problems

Discussion in 'Plumbers' Talk' started by jsaipe, Dec 7, 2013.

  1. Hi Ian.

    You're welcome, and £iver on its way.

    The EV itself won't leak water - at least not any significant amount.

    If the diaphragm inside it ruptures, you will possibly get air going into your system, but this will be expelled if your boiler has an auto-air vent. But this will cause the pressure swings.

    First thing is to test the EV by pressing the shraeder valve and also taking a pressure reading from it.
  2. Gas Man G

    Gas Man G New Member

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  3. That is a SUPERB article :).

    (I'm redundant... :oops:)
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  4. Gas Man G

    Gas Man G New Member

    I hope I posted it in the right place?
  5. Yes, on the plumber's forum.

    But I think it's worth posting it again on this same Plumbers forum but under a NEW thread and its own title - "Troubleshooting COMBI PRESSURE Problems" or summat?

    Are you planning to do more of these?
  6. Gordon Clifton

    Gordon Clifton New Member

    A cracking and hugely useful contribution by Devil's Advocate.
  7. The £iver's been taken, pal.
  8. Gordon Clifton

    Gordon Clifton New Member

    I can now go into battle with SSE who changed the EV and the pressure relief valve and left me with a system which, set to 1 bar cold, goes up rapidly to 2.5 bar when running. Once the evening's heating is over the pressure drops to under 0.4 bar. Next day, I recharge it via the filler loop and off we go again. For years before they changed the EV and PRV the system would be 1.0 bar cold, 1.5 bar when running. One day it dropped to zero, in came the cavalry three times, and now they've gone and left me with it. However, from this afternoon I know a bit!!
  9. What are your thoughts about this, Gord?

    Do you think they may have neglected to air-charge the EV when they fitted it?

    Did it do this 1 to 2.5 bar malarkey right after they replaced the EV?
  10. Gordon Clifton

    Gordon Clifton New Member

    I'm back after another test run over several hours. I don't think I mentioned previously that the boiler is a Keston 80, installed around 2003.

    First off, I blanked off the bathroom radiator because I found corrosion along its underside. I set its temperature control valve to the 'off' position but later this morning I will buy a blanking cap just to make absolutely sure. Note that there is no water staining on the floor underneath the radiator or on the radiator itself.

    I started yesterday's test with an indicated pressure of 0.9+ bar. For the next 90 minutes the boiler cycled on and off as I would expect running between 2.4 and 2.5 bar. All 8 radiators worked as expected. For the test I put a tissue in the open cup into which the PRV overflow goes - it's T'd into the condensate pipe. There's green evidence around the pipe opening of previous water egress! The tissue remained dry throughout. Eventually I shut the system down manually. Four hours later the indicated pressure had reduced to 0.65 bar. This morning, 13 hours after shutdown, the pressure was 0.6+

    When I checked the newly installed Elbi EV I found the fitting seemed to be inverted compared compared to other pictures I've seen, ie. the water section is on top. I couldn't see a Schrader valve but I assume it is under a plasic cap on the underside which appears to be screwed down. However, I checked that the top half was hot and the lower half cold. I don't want to fiddle with the plastic cap in case the returning SSE bloke(s) complain that I've been doing stuff that I shoudn't.

    From all of this I've concluded that:

    i) the high pressure problem which has always been an issue is still an issue. However, now that the PRV and EV have been changed the most likely cause is under-inflation of the EV although a new unit is supposed to be pre-charged to a nominal pressure;

    ii) given that the tissue test was negative, the PRV has not operated despite the running pressure being close to 3 bar. From this it would seem that the difference in the cold - cold pressures (0.9+ bar to 0.6+ bar) is due to leakage either in the central heating plumbing and rads or in the boiler. I've read that it is possible to isolate the CH plumbing and the boiler to determine which system is leaking. The last SSE bloke simply said that I had a leak and went on his way.

    I'll put a blanking cap on the bathroom radiator and run this test again. Assuming the result is the same I will write to SSE and invite them back to do whatever it is they should have done. I'll suggest i) pumping up the EV, or explaining what else it could be, noting that the Keston flying instructions specify 1.0 to 1.5 bar and ii) at least pinning the leak down to either the boiler system or the CH plumbing.

    That's it - a week ago I knew nothing. Now I know nothing+!
  11. Gordon Clifton

    Gordon Clifton New Member

    PS I've just realised it's a Worcester forum but the principles and problems seem to be applicable! When my Keston eventually joins its brethren on the eternal boiler scrapheap I intend to replace it with a Worcester so maybe that's a good enough excuse for being here!
  12. Tee-hee - this is a Worcester forum?!

    Nope - it's a trade and DIY forum - anything goes. Even Keston... :rolleyes:

    Ooookkkaaaayy. That's some good testing. But shame you weren't able to check the EV air pressure.

    Anyhoo, that bathroom rad is likely chust to have external corrosion due to condensation trickling down and gathering along the bottom edge - mine is the same :oops:. If, however, you want to isolate it, you need to shut off both valves.

    But, I wouldn't blame the rad for this leak - or else it would be obvious.

    Okay, the huge increase in pressure when the boiler runs can only be - afaIk - due to an under-inflated/faulty EV. So, there is an issue there, whether he didn't fit it properly or else didn't check the pressure. (Either way, that is sooo basic he should be shot.)

    I'd email Keston and ask about which way up it should be fitted - if it makes a difference.

    Does having it 'upside down' make the Shrader valve more difficult to get to?

    That still leaves you having a pressure loss, presumably when the pressure is high. It seemingly ain't coming from the PRV or condensate pipe, so that does seem to leave it being a real 'leak'.

    That ~0.3 drop in pressure ain't huge, but it would still - for most systems - mean, ooooh, a half-cup of water? Ie - you would notice it.

    So, if it ain't from the PRV or condensate or rads, then it must be from a pipe?

    Do you have any external drain cocks for your system?

    A different issue is that you mention that the PRV discharges into the condensate pipe? Bludy hell.

    Ok, I'm not a plumber so I don't know if this is 'ok', but it sure strikes me as being well dodgy...

    For a start, the condensate pipe MUST be plastic and not copper, and the PRV discharge but be the opposite. How do they square that conundrum?

    Also, I think you are meant to be aware if your PRV has opened - how can you be if the discharge is hidden amongst the cond?

    What installed the Keston this way?
  13. albapa

    albapa New Member

    Hi all,

    First of all, thanks to Devil's Advocate for the suggestions, they have been extremely helpful. For the benefit of others reading this thread, I describe what happened in our house:

    1) The boiler is a Worcester 27 CDI combi boiler.
    2) Shortly after moving in, we noticed that the pressure in the system gradually decreases. We topped it up, but obviously, it happened again and again. There was no obvious leak at the PRV.
    3) We shut off the system and closed the boiler isolation valves (central heating feed and return, mains cold in, hot water out) and the boiler held the pressure very well - this reassured us the boiler should be fine.
    4) After some searching, we found out that the leak is from a central heating pipe, buried under the living room floor in the screed. The culprit was a failed plastic push fit elbow.
    5) We fixed the leak, the central heating was up and running...
    6) ... except now the pressure was increasing. From 1 bar over the course of a week and a half, it gradually went up to the point the PRV started releasing pressure.
    7) We replaced the filling loop with a new "keyless filling loop" and know everything seems to work very well.

    I think the previous owners have never removed the key from the filling loop - most likely because the valve was leaking, and removing the key let mains water dripping out constantly from the filling loop. So they left it in as a fix. This wasn't a problem, because the system must have been leaking for some time and what went in, also came out, under the floor. Once the leak was fixed, though, the pressure started to increase... Luckily, there seems to be no damage to the wall of the house.
  14. KIAB

    KIAB Super Member

    Expansion vessel, ruptured diaphragm I suspect.
  15. albapa

    albapa New Member

    Not in my case - replacing the filling loop would not have fixed that. Also, the pressure would have increased as the temperature in the system increased, not gradually over two weeks.

    But it's all good now.
  16. Thanks for the report, Albapa.

    Was it a 'mare locating the leak? And what was it that had happened to the P-F fitting? Was the fitting itself buried in the screed? Was it covered first with lagging or similar?

    Pleased it's sorted. One thing I'd add - literally and metaphorically - is that your system water is unlikely to have any inhibitor remaining in it, so it may be worth partially draining down a rad and adding some?

    Or, do you have a magnetic filter on the return pipe? If so, you can often add chemicals through there.
  17. albapa

    albapa New Member

    It could have been a nightmare, but we were "lucky": my 5-year-old son and myself were in the process of removing lining paper from a section of the wall and we noticed that the bottom of the plasterboard was wet. First I thought it'd be damp, but then we quickly realised it was totally soaked and crumbling. We broke away a considerable chunk of it, removed a few pieces of engineered wood flooring and confirmed that when filling the CH system, a nice pool of water forms in the gap between the wall and screed. Then it was a matter of breaking the concrete. The piping is plastic, lagged in some duct tape, and I think there was some on the elbow as well. No idea what happened exactly - although the piping was not supported very well, so it could have been knocked or something.

    Thanks for the suggestions. When I was fixing it - two months ago now - I drained and refilled the system a couple of times and when I did my last filling, I did add a good dose of inhibitor. Some of it will have been removed later when the system was overfilling, but as I added a whole dose enough for a 100 litre system, it should still be plenty (as my system can't be more than 40 litre). I'm planning to replace at least one rad, plus remove the whole section of pipework buried in the screed so it'll be drained again and refilled with inhibitor fairly soon.
  18. KIAB

    KIAB Super Member

    Magnaclean partically good.
  19. Jitender

    Jitender Screwfix Select

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  20. Nidge.57

    Nidge.57 New Member

    Just joined the forum so I could say thank you this sorted all my problems. So nice to find a forum with knowledge and not ideas.
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