Glow worm 18sxi gaining pressure

Discussion in 'Plumbers' Talk' started by Alex Jungius, Aug 14, 2015.

  1. Alex Jungius

    Alex Jungius New Member


    I've got a Glow Worm boiler that has slowly been increasing in pressure over the last few weeks when off. I've had a plumber round to look at it and he said the expansion vessel was dead. Water came out of the valve when he pressed it. He's replaced the vessel and checked that the filling loop is not passing any water and it's not but it's still gaining pressure. I'm not sure what else it could be. Also, the boiler is just for the central heating and does no hot water as I have a separate water heater for that so I'm stumped as to what could be causing the pressure increase.

    Any ideas?

  2. Despite your protestations the filling loop letting by is the most likely explanation. Have you actually disconnected the filling loop?
  3. Dave does Gas

    Dave does Gas Screwfix Select

    What he said :)
  4. Alex Jungius

    Alex Jungius New Member

    Yes, the filling loop has been disconnected since the weekend and still increasing in pressure.
  5. Dave does Gas

    Dave does Gas Screwfix Select

    Which model is it?
  6. Alex Jungius

    Alex Jungius New Member

    It's a glow worm ultracom2 18sxi
  7. Glad its Friday

    Glad its Friday Active Member

    Yours is a system boiler. If you are having a steady pressure increase then that can only come from the mains water somewhere. If you have no hot water cylinder then the only place is the filling loop, but you've said this is disconnected.

    So I suspect you may have an additional top up point somewhere that has now started to let-by.

    What pressure does it get up to and is this your mains water pressure.
    In normal operation the water pressure will rise and fall as the water heats up and cools down. Typically if cold at 1bar it will get up to c1.5 bar when hot.
  8. Alex Jungius

    Alex Jungius New Member

    I've hunted high and low and can't find any additional top up points. I've literally traced all the CH pipes.

    I have bled all the radiators in the house and that dropped the pressure down to 1.1 bar but overnight it's crept up to 1.4 with the heating off still. I've looked at the filling loop again which is off (disconnected completely) and there is actually a tiny leak coming from the central heating valve that the filling loop connects to. Surely this should be decreasing the pressure?!
  9. Alex, pressure increase with the boiler not heating can only (I'm pretty sure) come from mains water getting in to the system. Mains water is the only source which will be at a higher pressure than the system pressure.

    You've disconnected the filling lopp completely. So it ain't that.

    That leaves two further possibilities: (1) the IS another filling loop elsewhere. I know this is unlikely, but there was a near-identical post a few weeks back with this exact same issue and an owner going nuts. Guess what he finally found behind some kitchen units? Yup - a second filling loop...

    Or (2) Something else... :rolleyes:

    Does your system boiler supply a 'Megaflow'-type hot water tank? Ie - one that's pressurised at mains pressure? If so, that's a likely source.
    Alex Jungius likes this.
  10. Alex Jungius

    Alex Jungius New Member

    Hey, thanks for the reply DA. The system is just a central heating system so no hot water or hot water tank. I will check again that there isn't another fill loop anywhere but I traced all the pipes last night and couldn't find one on the entire system. What do you think the likelihood is of it being the pressure sensor?

  11. The pressure sensor giving a false reading?

    They can certainly go faulty like any component, but to give a steadily increasing readout? Blimey.

    Good thought, tho'.

    When you say the pressure increases - do you do anything to stop it? Eg - do you drain off any water to lower the pressure again?

    What pressure does it ultimately get up to? It should open the PRV and dump the excess when it gets to ~3bar - has it ever done this?
  12. Alex Jungius

    Alex Jungius New Member

    Yeah, the pressure tends to be a steady increase over the course of days rather than any huge jumps or anything. The reason I noticed it in the first place was the boiler was flashing a fault code and the pressure had climbed to over 4 bar without the release valve opening so had that sorted and cleaned out and now works but recently I've been just bleeding the radiators to release the pressure. I was thinking of just turning the heating on to see if getting the pump going and heating up the water could regulate things. No science behind that thought but it seems sometimes boilers tend to flare up when not in use for a long while in my experience.
  13. Well, if the pressure rises to above 3 bar and the PRV now opens to dump the excess and the pressure keeps rising again afterwards, then it ain't down to a faulty pressure sensor :)

    Unless it's one that produces water from electricity.

    In which case remove it. And send it to me...

    So, it looks as tho' - almost certainly - you do have mains water getting in to your system.

    And I haven't a bludy clue from where... :oops:

    Where do you get your hot domestic water from, if not this boiler?
  14. Alex Jungius

    Alex Jungius New Member

    Good point, I didn't think about the PRV only releasing if the pressure was genuinely above 3 bar. My hot water comes from a separate Britony water heater which is a completely separate system. Think I'm going to check the whole system again for rogue filling loops that I might have missed.
  15. Alex Jungius

    Alex Jungius New Member

    Definitely no other filling loops. All the pipes in my house are very easy to follow and where I can't see them I know there aren't any water pipes so it's definitely not filling from somewhere else. Stumped!
  16. Ok, is your boiler being used at all at the mo'? I'm guessing not.

    Is the pressure still creeping up? If so, how do you release it?

    Ok, try this. Turn off the power to the boiler so's it doesn't fire up for any reason (pump anti-seize, etc).

    Turn off the flow and return CH pipes under the boiler - there should be quarter-turn valves fitted.

    See if the pressure still increases.

    If it does, then it's unlikely to do with your radiator circuit.

    So it'll be down to one of the other pipes heading in to your boiler.

    So, have a cuppa, rest your face in your hands for a few seconds, clear your head, forget all pre-conceptions, and walk back to your boiler and go "RIGHT! This pipe first - what is it, and where does it go?"

    (Or does your filling loop feed in to a CH pipe on the rad side of the isolating valves?)
  17. Alex Jungius

    Alex Jungius New Member

    I release the pressure by bleeding the radiators to keep it in the normal range. It doesn't go up quickly, just incremental amounts over a few days. The filling loop isn't actually near the boiler but goes into radiator pipework on the other side of my utility room.

    I've got to pop out now but will try what you've said when I get back in. Thanks so much for taking the time to have a think about my problem.
  18. Alex Jungius

    Alex Jungius New Member

    Hi, I tried this and the pressure stopped increasing overnight. I've looked everywhere and there are definitely no other fill loops on the whole system. I've traced every single bit of pipework, under floorboards and in skirtings. The one way valve is still leaking and even though the wing nut is screwed on tight it's actually coming out of the join between the hose and the one way valve. When I un-do the valve there is quite a lot of pressure built up from the leak filling the fill loop pipe. I don't suppose this pressure could be opening the other side of the valve or doing something strange?
  19. Don't quite follow what you're saying about the one-way valve and filling loop, but I'm sensing that the 'loop' is still actually connected? Any chance of a photo?

    Oookkkaaayyyy, you have now checked that there are no other filling loops or connections to the mains? Cool. And you have tried isolating the rad system (which includes the single filling loop) and this stops the boiler pressure increasing? Nifty. And this increase in pressure can ONLY come from a mains water supply? Ok. And the ONLY connection to the mains is via the filling loop? Getting somewhere now. AND that filling loop is still connected?

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