Worcester Bosch Greenstar 29 CDi Classic ErP - new boiler losing pressure when heating off

Discussion in 'Plumbers' Talk' started by djs43, Feb 12, 2017.

  1. KIAB

    KIAB Super Member

    Seems like system was nearly totally empty.
     
  2. djs43

    djs43 New Member

    That's what I feared hearing. Dare I ask how much water is in the average CH system? And out of interest what does the 29 in the boiler model 29CDi refer to please? Thanks.
     
  3. The number usually refers to the max kW output - so yours will be ~29kW (which roughly equates to a DHW flow rate of around 12 litre per minute).

    Don't worry - your system has not actually emptied! With a sealed system like yours, all that happens is that it only leaks out the bit of system water that's under pressure - a few cup-fulls. Once the pressure reaches zero, there is nothing pushing out the water any more, and also no way for air to get in to replace any water trickling out, ergo - no more water actually comes out.

    But zero pressure is not good. I'm surprised your boiler still works - it can't have a pressure sensor in it, I guess.

    So, yes, always get it up to at least 0.5 bar or so before using it.

    Good luck with the camera - fingers crossed :)
     
  4. djs43

    djs43 New Member

    Thanks DA - so we should see the pressure gauge go up if adding water to it without boiler having to be on yes (we have an analogue gauge)?

    Thanks for the good luck, think we'll need it the way things have gone with this house to date, will keep you posted!
     
  5. I'd be wary of turning on the boiler if the gauge is hard on zero when cold; I'd like that needle slightly off the bump stop at least! If you know that the pressure always increases up to a 'suitable' point when hot - ie around 1 bar - then I'd only top it up enough to get to that basic stage.

    Anyhoo, you only have to cope with this for a couple more days... He hopes.
     
  6. Remloc

    Remloc New Member

     
  7. djs43

    djs43 New Member

    Hi all, thought I'd post an update, although not really much of one tbh. So we have a claim pending with house insurance which is still with underwriters although will mean £750 excess - although given the cost involved with leak detection specialists and then the potential remedial work (as likely having to refloor etc.) we figure as gutting as it is after just spending best part of £5k on new CH system we probably just have to suck this up sadly.

    I don't know if this signifies much but earlier my other half noticed that the closest rad to boiler (a new vertical one in hall) was only warm on the last column - upon checking/bleeding, it had an awful lot of air in it.

    I have checked most of the others, which had air too but not as much as one above - although one in one of the bedrooms upstairs has got so much I can't get water to come out of it without boiler pressure dropping right down. I'm wondering does this mean there is likely a leak going to this one (even though we were assuming leak is downstairs due to nothing visible on ceilings)?

    Also is it normal/to be expected with all the water topping up we're having to do that we would expect so much air in our system?

    @Remloc - the installer has said his guarantee does not include existing pipework (and he is obviously assuming this is where the problem lies).

    As always, thanks for input/help all.
     
  8. koolpc

    koolpc Super Member

    Interesting thread, some great advice. Be interested in the outcome.
     
  9. That much air will not have come from sir dissolved in the top-up water, so I can;t see it coming from that. Sometimes you'll have gas forming due to corrosion, but I doubt very much it's that either - there's too much.

    So, where is it coming from? I dunno... :oops:

    The usual suspects are a faulty exp vessel in the boiler - the pressurised air side seeps through the membrane and enters the water. But it doesn;t seem as tho' your boiler is that faulty or else the pressure would SOAR when it's hot.

    Pure guess - 'cos I'm stumped - is that your system gets up to 1 bar when hot and the water has expanded, but leaks water all the time - so by the time your CH turns off the hot pressure is at near zero. What happens then? The system water cools, the water volume contracts - and you actually end up with a negative pressure in your pipework!

    This then sucks air in through the same leak where it loses water.

    That is a total guess...

    That rad wot has lots of air - is that the one that's leaking, you ask? No - 'cos you'd see them cupfulls of water on the floor.

    This is obviously only a best guess, but I suspect your leak is on a pipe under your ground floor - for all the reasons we mentioned before.
     
    djs43 likes this.
  10. djs43

    djs43 New Member

    Thanks for that DA. Couple of follow-up questions (as usual!):

    -Am I right in saying the isolating of the CH pipework from boiler test I carried out prior 'proves' the EV is definitely not at fault here (I only ask as a family friend with a similar newish boiler had a fault with this part apparently)

    -Should I be worried that when I bled the rads, the water that appeared on a couple seemed to look a bit 'rusty' instead of clear like when the installer bled them the other week? I ask this given what you said about corrosion being a possible issue in regard to all the air in the system?

    Getting nowhere fast with the insurance company having just chased... again.
     
  11. palavaman

    palavaman Well-Known Member

    Not followed or read this thread much, but why is the installer not taking some responsibility for this ''problem''? The whole purpose of installing a new boiler is that it works. In my view, th boiler is not doing what it is meant to do, work (to a satisfactory standard).
    When you are doing a Combi to Combi swap, you ofcourse need to find out and confirm why the customer wants a replacement to their current boiler? Is it just because the boiler is old? Is it because it is faulty? If faulty, what are the fault symptoms - constant falling pressure, constant resetting, etc.
    If converting from gravity to combi, then you MUST carry out a pressure test. There are pressure testers out there (see Screwfix product code: 83797 - Pressure Testing Pump). Pressure system up to at least 1 bar and find out if pressure drops over a period of time. If you can't be arrzed to use a pressure tester or haven't one, then pressure system up to 1bar or 1.5 bar and leave overnight. Check the following day and if pressure has dropped, then it's time to investigate and rectify. A gravity system may have been leaking for years and no one will be the wiser as the header tank automatically tops up the system. Installing a Combi or sealed system will quickly identify that there is a leak somewhere.
    As for air in new radiator, air replaces any lost water. So the higher the radiator, the more air you will have in there.
    The installer should have come to an agreement with the homeowner/customer to help resolve this problem. In my opinion he should have realised that there was a leak from day one after commissioning the system. I,m not impressed, Why not consult the customer after commissioning the system and say something like: ''I think we have a problem? I have installed the new boiler and after firing it up, there is a leak which I have not been able to trace from any of the exposed pipes. So I believe the leak may be under the floorboards. To gain access to the pipes, carpets etc have to be removed and I will charge extra to cover labour costs. You will have to get a carpet fitter in to refit the carpets properly.'' Then you two can sit down and work out a way forward. Such an arrangement would have worked out cheaper than the £750 excess you say you may have to pay your insurers.
     
    djs43, koolpc and Mike83 like this.
  12. I'd agree with that - it's unlikely to be the exp vessel as a faulty EV shows other symptoms as I said before - the pressure would shot up dramatically as the system heats up. But also, as you say, when you tried isolating the boiler it was clearly the rad side that was loosing pressure, not the boiler.

    I wouldn't be too surprised that there was some hint of rusty water in the air-filled rads since water + air = rust :p

    However, I wouldn't be too concerned at this early stage, and I also wouldn't suggest that the 'air' is actually hydrogen gas given off during such internal corrosion - there's simply far too much gas there.

    I don't see any real alternative now to taking up floors, but that's for a pro to decide.
     
    djs43 likes this.
  13. djs43

    djs43 New Member

    Hi guys, just another non-update update to say we had a specialist leak detection company booked for today (not via insurance currently as proving an awful lot of hassle) but they cancelled first thing due to engineer illness... maybe we're just not supposed to have working CH! Will update when they are able to come out. Cheers.
     
  14. TheMorg

    TheMorg Active Member

    To be fair to the installer if you are pressure testing pipework before fitting the boiler there's a possibility it's going to hold, then after you've properly flushed it the leak shows up. Also what are you supposed to do if you've got a leak, it still needs to be located. It makes very little difference if it's leaking on a new boiler or old. I'd rather replace everything that will be replaced when fitting a new boiler, ruling out the removed pipework, rads etc, then find the leak from there.

    I don't pressure test existing pipework prior to fitting a new boiler (I'll ask if the pressure holds on a sealed system), and don't know any plumber that does. I also don't know a single plumber that would take responsibility for existing pipework (that doesn't mean we won't spend an hour or two trying to find the leak for free, beyond that and everything is chargeable).

    OP - your best bet is to buy a FLIR camera for you smart phone off ebay, then see if you can find the heat trace of a leaking pipe. Once done sell it on ebay again and it will only cost you £20-£40. You can also check your installer has done a proper job of flushing radiators.
     
    djs43 likes this.
  15. djs43

    djs43 New Member

    Thanks the info, just out of interest what would I be expecting to see image wise on such a camera where the leak is and what would I want to see to confirm the installer had properly flushed the rads? Cheers.
     
  16. TheMorg

    TheMorg Active Member

    You might see a hot spot where there is a leak, it will also enable you to at least trace where all the pipes run to keep the disturbance to a minimum.

    With radiators you should have a reasonably balanced orange heat image of the entire surface (not a blue cold spot in the middle, indicating they haven't been flushed very well).
     
  17. djs43

    djs43 New Member

    So it would be best to run the heating at a high temp for a while before right? Any idea if it would detect given I believe the downstairs pipework is in concrete under timber flooring? Thanks.
     
  18. TheMorg

    TheMorg Active Member

    It should be fine to trace under concrete, running the heating will enable you to identify the leak easier.

    It's not guaranteed, but well worth trying for a small outlay.
     
  19. djs43

    djs43 New Member

    Given the company can't come until late next week, I have one ordered arriving tomorrow. Will let you know if/what we find!
     
    Deleted member 33931 likes this.
  20. palavaman

    palavaman Well-Known Member

     

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