Green star 24i no pressure

Discussion in 'Plumbers' Talk' started by Richard Rendle, Feb 28, 2015.

  1. Richard Rendle

    Richard Rendle New Member

    hi I have the above boiler which has at times no pressure.

    I re pressure it to 1 bar and sometimes it will last for 18 hrs. Then it goes to zero, I have to take air out of the radiators. and re pressure it, sometimes it drops instantly and others will last up to 14-18 hours.

    We have had an external expansion chamber, but it has done nothing to help the problem. I have been told there could be a leak somewhere, so need to channel out the radiator pipes to see if there is a leak. Help
     
    Last edited: Feb 28, 2015
  2. plumber-boy

    plumber-boy Well-Known Member

    Your expansion vessel may need recharging with air,lots of videos on YouTube to show you how.;)
     
  3. Richard Rendle

    Richard Rendle New Member

    Thank you
     
  4. Richard Rendle

    Richard Rendle New Member

    Just to let you know this big red expansion vessel was only fitted a few days ago, and after the engineer left it lost pressure again
     
  5. plumber-boy

    plumber-boy Well-Known Member

    Could be a Pressure Relief Valve (PRV)or a cracked heat exchanger or just a leak on the system,without looking at your system it's very hard to say.
     
  6. Richard Rendle

    Richard Rendle New Member

    Thank you once again for your help. If it was the heat exchanger, would there be excessive gasses from the vent/chimney.

    Also wouldn't there be signs of a leak inside the combi unit, as it seems to hold the pressure overnight when all is shut down,

    Look forward to your reply.
     
  7. plumber-boy

    plumber-boy Well-Known Member

    If it's the heat exchanger it will lose system water down through the condense pipe so you wouldn't see it.
    My guess would be a leak on the system, or the PRV letting by.
    Call your engineer back out as I'm guessing this was the issue you originally had them out for,if they're on site it shouldn't take them that long to find the problem, depending on their skill set.
    GOODLUCK...
     
  8. Richard, you charge the system up to 1 bar, and sometimes as quickly as 18 hours later it has fallen to zero? And also in that time you may have to bleed some air from a rad(s)?

    How much air? How long do you have the bleed valve open for?

    Even if you had corrosion going on inside, it wouldn't produce significant amounts of gas in 18 hours, I don't think.

    And sometimes the pressure drops almost right away?! Blimey.


    You asked plumber-boy "If it was the heat exchanger, would there be excessive gasses from the vent/chimney?" Why did you ask that - have you been seeing extra whitish plumes? I guess it's possible that if the exchanger inside the burner is leaking, it could produce more 'steam', but as explained above, most water in there would just drain out with the condensate and you wouldn't see it.


    You've had an external exp vessel fitted? Why? Is it to replace the boiler's faulty one, or to act as an extra vessel 'cos they reckoned it would help?


    Ok, sitting comfy? Right, I'll begin... (All of this might not apply to you, but I chust couldn't be bovvered writing it all again...):



    You definitely have a leak. Somewhere. We know this 'cos you keep filling it with water to raise the pressure, and the pressure keeps falling.

    So, where's the leak...

    When you say they fitted an expansion vessel, I'm guessing what they actually did was fit a second exp vessel, as there is almost certainly already one inside your boiler casing. A second one is sometimes needed when a boiler is fitted to a larger than average rad system (how many rads do you have?) and the built-in vessel ain't big enough to cope with the expanding water when the system heats up.

    (Water expands when heated. Your system is sealed, so the pressure in it would soar dangerously if the excess water didn't have somewhere to go when it was heated, and that place is the exp vessel. The exp vessel is a vessel. Inside is a rubber diaphragm with space for the system water on one side and this is counter-acted by compressed air on t'other. When the system heats up, the displaced water goes into that vessel and squishes that rubber dia against the compressed air. When the system cools down again, the comp air pushes the water back into the system. Your pressure should therefore remain fairly steady throughout.)

    So, where could this water be going? A few places; First possibility, a simple leak in your system. A faulty pipe fitting. A dodgy radiator valve. Etc. I take it you've gorn round your whole system and checked? (It would be a sizeable puddle...) Of course there's always under the floor - any way you can access this to check?

    I've chust read on a different thread how to check for such simple leaks, but it does mean turning your boiler orf for a day so you'll have to use other heaters and kettles... Top up the system pressure to 1.5bar as before, switch orf your boiler (leave a note on the isolating switch so no-one turns it back on...) Look under your boiler at the 22mm CH flow and return pipes - they should each have a quarter-turn isolating valve on them where they join the boiler. Turn them both fully off.

    Leave the boiler for a day. Check the pressure. If it has dropped, your leak is inside your boiler. If it's still at 1.5bar, the chances are your boiler is ok and the leak is elsewhere. Now open the flow and return valves - does the pressure suddenly drop? If so, you have a leak on the rest of your rad pipework, so start searchin'.


    Ok, if the fault is instead 'inside' your boiler, the first possibility is a faulty PRV, Pressure Release Valve. This valve is set to open at around 3 bar pressure to dump the excess water out a 15mm copper pipe outside your house, hopefully safely at the ground. This valve is usually triggered when the exp vessel has gone faulty, such as having lost air pressure. Easy to check this - find this pipe end outside your house, and wrap a poly bag over it with a bit of tape. Monitor this for water over a couple of days with your system running as normal. If there's water in it, that's your loss chust there, and you need a new PRV - £35 + a half hour fitting, total <£100.

    Of course, if your boiler pressure has reached nearly 3 bar due to some other issue, then this valve WILL open and dump the water - as it should. So, what I'm sayin' is, if there is water coming out that pipe with the pressure only reaching about 2 bar, or even if the boiler ain't even running, then you have a faulty PRV.

    Surely to gawd that the plumbers have tried all this?

    Third - nastiest - possibility is that your boiler's heat exchanger is bust. This is an expensive part - probably £200-£300 - and a major job to swap, so expect a bill of around £400+, I guess... (Ie - possible new boiler time...)

    Water from a leaking exchanger would most likely find its way out the condensate discharge pipe. This is a 22mm plastic pipe, again likely to be heading outside into a drain, but could be connected to an inside drain too. When your boiler is running, this pipe should send glugs of water out at regular intervals anyway, so the secret is to work out if it's actually 'leaking' water instead. I guess if water comes out with the boiler turned off - ie: not running and producing condensate - then it's definitely 'leakage'. Possibly if the water trickles out rather than come in 'glugs', then it could be leakage. But the first indication is the clearest.

    Not sure if I've missed anything, but I'd have thought that the above should determine the area of water loss.
     
  9. Richard Rendle

    Richard Rendle New Member

    Is the condense pipe a plastic pipe, if so I did mention to my plumber that the plastic pipe which is running down next to the copper pipe was very hot, so I initially followed the pipe underneath the bath away from the heat source it was plumbed into the waste pipe of the bath and it was still hot. Is this normal when the boiler is working. I did mention it to our plumber and he said this was nothing to do with it.

    One last thing we have a problem all the radiator pipe work is under the floor set in concrete we have pulled up all the carpets and can't see any evidence of leaking, you can understand my reluctance to dig all the floor up. So trying to eliminate everything else before I do so.

    Appreciate your input thank you very much. You have been very helpful
     
  10. Hmmm, interesting...

    I've chust tried touching my condensate pipe (yes, it's the plastic one) and it's luke-warm at most, and that is right up at the boiler. Condensate liquid will be trickling down from the secondary exchanger which sits in the flue gases. The gases from condensing boilers are much cooler than on conventional boilers - you can keep you hand in it very comfortably (except the acid will corrode you away...)

    So, I'm not surprised that the condensate liquid is also quite cool - ie gently 'warm' at most.

    However, system water is hot, probably around 70o-80oC, so you may well have struck on something there. If you have, as you know it ain't good news...

    If you read through my tome above, you'll see the way to check if it's your rads and pipework is to isolate it all at the boiler - easy to do, but you cannot run your boiler for that time.
     
  11. Richard Rendle

    Richard Rendle New Member

    Thank you very much for your advise, the next thing to do would be to isolate the boiler for a day, and then go from there.

    Once again thank you for help
     
  12. No prob.

    Keep us posted, please - its an interesting one. And it'll help other to see how you (hopefully) isolated the fault.
     
  13. plumber-boy

    plumber-boy Well-Known Member

    Yes good luck Richard,keep us posted.
     
  14. Richard Rendle

    Richard Rendle New Member

    Will do
     
  15. Darn - I tried to ignore it.

    It's 'advice'... :p
     
    plumber-boy likes this.
  16. plumber-boy

    plumber-boy Well-Known Member

    DA,you just can't resist can you.:)
     
  17. I'm sure you tried to leave a space betwixt 'DA,' and 'you'.

    But failed... :rolleyes:
     
    plumber-boy likes this.
  18. plumber-boy

    plumber-boy Well-Known Member

    I'm allowed DA, I'm stupid.:oops:
     
  19. Shush, you. :rolleyes:
     
    plumber-boy likes this.
  20. plumber-boy

    plumber-boy Well-Known Member

    I can't compete. 1425244259267.jpeg 1425244259267.jpeg
     
    Deleted member 33931 likes this.

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