Worcester 28CDi help-losing pressure and making strange noise

Discussion in 'Plumbers' Talk' started by GC17, Nov 6, 2014.

  1. GC17

    GC17 New Member

    Help! My Worcester 28CDi has had pressure problems for a while - but since turning on the CH this week it is dropping drastically to the point were we currently have no heating or hot water :(

    It has always dropped pressure SLOWLY since I bought the house 3 years ago and needed topping up every few months (no major deal). However, after refitting a radiator which had been off for replastering a few months ago obviously the pressure dropped in the system. I meant to top it up after dinner but totally forgot and turned on the hot water to do the washing up (ooops!). No hot water came through and when I went upstairs to the boiler it smelt slightly of burning and a red light was flashing (domestic water demand indicator). The appliance re-lit after the appropriate waiting time and appeared to be ok but it has been losing pressure at a more steady pace ever since.

    After reading up significantly on the system and how it worked I also discovered the air vent at the top had been totally shut instead of being very slightly open. I hoped this had solved the problem but I was still having to top up every couple of weeks to get back over 1 bar of pressure. Since we've turned the heating on this week (only for a couple of hours in the evening) the problem has been significantly worse. Last night I topped up pressure to 1.5 bar and when we turned off the heating 2 hours later it dropped to 0.9 bar and overnight has gone down to 0.5 bar :( Also - we've noticed the fan/pump(??) is has started making a squeling noise when the CH first comes on.

    It seems there is a significant problem with the boiler retaining pressure - has anyone got any ideas? I'm wondering from what I've read if there's a problem with the fan/pump? None of the radiators are leaking and we'd know if any of the pipes were leaking this much under the floorboards!

    Any help gratefully received - I've just paid for carpets (after 3 years without!) so can't afford a massive plumbing bill!
     
  2. Dave does Gas

    Dave does Gas Screwfix Select

    Have you noticed when your heating is on if the pressure guage on the boiler has risen significantly or is there a discharge outside from the PRV outlet? Other than that there has to be a leak somewhere on the heating system. There are leak sealing chemicals that can be added to a system to seal small leaks, but from what your saying its a bit more than small.
     
    FatHands likes this.
  3. GC17

    GC17 New Member

    Yes.....the pressure gauge does rise significantly when CH is on. Im not sure about the overflow but could turn it on again and check. Slightly concerned about using the boiler at all now tho as the pressure drop is getting so severe and I dont want to damage anything further.....!
     
  4. Hi GC.

    I wonder if you introduced air into the system when you fitted that new rad - did you open the rad valves (with the boiler off) and bleed through the nipple until water came out?

    Obviously the system pressure would drop dramatically when filling an empty rad; in fact it would probably reach zero before the rad was actually filled so perhaps this rad was never fully filled with water?!

    Anyways, a small loss of pressure is not unusual and considered 'normal' - eg tweaking it back up from, ooh, 0.5 bar to 1 bar every 6+ months I'm guessing (tho' my system, which was fitted by an expert, doesn't lose any pressure at all. Ever. Just thought I'd mention that :rolleyes: ), but I certainly wouldn't like it to be more than that.

    The pressure loss you are experiencing is a problem, obviously.

    Where does the missing water go? There's a few possibilities; a leak in the pipework, rads or valves. An internal leak in the boiler - perhaps the main exchanger, and the water is being drained off with the condensate (I think that's possible?) so you won't notice it. Or - phew - the most likely is your safety release valve which is allowing water to seep by.

    Them SRVs are a sod for dripping - not resealing properly - once they've been 'activated', and they are activated by the pressure going up to around 3 bar - the safety limit.

    So, first thing as dave says is, have a looksee at the outlet of this safety discharge pipe - it should be 15mm, copper, and be outside the house, possibly pointing into a drain. Put a cup under it and repressurise your system back up to 1 bar.

    See if it discharges as the pressure drops.

    First, tho', bleed every rad in your system...

    You may also need to check your expansion vessel pressure - this is the drum inside your boiler which is meant to keep your system pressure steady as it heats and cools.

    But - bleed rads, and check discharge pipe first.
     
    FatHands likes this.
  5. Steambod

    Steambod New Member

    What he said.
    I've currently got a rad off for decorating and losing about 0.1 Bar a day due to the twin entry valve weeping (got a bucket under it and know where it's at). Normally heating systems will lose a little water for various reasons when running: pipework expands/joints move/a bit of weepage from air vents etc. but not noticeable because any drips usually evaporate. Check outlet from the relief valve on boiler to see if you're losing it that way as well.
     
  6. GC17

    GC17 New Member

    Thanks for your replies :) Yep we totally filled up that radiator and bled every rad in the system before turning the heating on. There is definitely something wrong with the boiler.....dropping from 1.5 to 0.5 in 2 just hours isn't right :( I'll re pressurise and turn the heating on and see if its leaking from safety discharge outside. I'm pretty sure if the leak was internal we'd have noticed a big mark on one of the ceilings by now!
     
  7. Ooookkaaaayyyyy...

    The chances are high that is it the safety release valve, so check that discharge.

    These valves sit inside the boiler for years doing nothing as everything is hunky dory. However, when the pressure does soar and it's called into action (dumping excess water), it is very common for it to not properly seal afterwards, and it allows a steady - and bludy annoying - trickle to continue, and your pressure carries on dropping even when the boiler is off.

    So if you could check that and report back, that would be cool.



    Further info on a possible culprit...

    Y'know what an expansion vessel is? It's a chamber inside your boiler casing which has a rubber diaphragm in t'middle. On one side of this dia is the system water - it's joined by a thin pipe. On t'other side is compressed air.

    The idea is that when your system water is heated, it expands and has to go somewhere - that somewhere is into that vessel where it deforms the dia and pushes against the sealed air on t'other side.

    If that vessel is faulty or isn't air-pressurised properly, then it'll be already full of system water, so when your system heats up the excess will no longer have anywhere to go. Problem.

    The symptom of this is - your boiler is at 1 bar, cold. You turn 'er on and the pressure rises rapidly as it heats up, often going way above 2 bar.

    When it approaches 3 bar, the safety valve opens and the excess water is ejaculated outside. Your boiler may run 'normally' but the pressure will remain high as long as it's on.

    Guess what happens when you turn 'er offski? The system water cools, contracts and the pressure plummets. It'll drop to below the original 1 bar 'cos there's now less water in the system.

    What does one do now? One tops up the water back to 1 bar, turns on t'boiler, and history repeats itself.

    After you tell us aboot the discharge, we can tackle the vessel if necessary.
     
  8. GC17

    GC17 New Member

    Afternoon! So.....repressurised the boiler to 1.5, turned on the heating......within 5 minutes or so it had raised to 3 bar and at 3.2 bar the discharge started to dribble water.....sounds like that could be the culprit! Thanks for the help diagnosing :) So.....what's our next step? Can we replace this part ourselves? I also think the charging link assembly needs replacing too as this has always been a bit dodgy and the knob for repressurising pops off so I have to turn it with pliers (not ideal!) Figure we may as well sort this at the same time!

    Also - since this pressure dropping issue the fan (we think) is making as slight squeeling noise when we turn the boiler on - is this part of the same issue? Or did we potentially damage the fan the day I turned on the hot water when the pressure was below 1 bar and overheated the system (I guess this is also when the expansion vessel was first put into use).

    Thanks again for all your help - very pleasing to have diagnosed the problem - now it's just a case of fixing it so we can have heating and hot water again!
     
  9. Dave does Gas

    Dave does Gas Screwfix Select

    No its not the PRV, that is doing its job, it is designed to relieve pressure at 3 bar so that is working correctly. Your culprit is the expansion vessel, it has probably lost pressure and is not absorbing the difference between cold and hot water. what you now need to do is isolate the boiler from the heating circuit by using the isolation valves under the boiler. Drain the boiler, then using a tyre pump preferably with a gauge top up the expansion vessel to 1 bar. Once this is done open the iso valves under the boiler and refill to 1.5 bar. If the pressure remains below 2 bar with the heating on mission accomplished. If not then you will need a new expansion vessel, Having said that if yours is the old style CDi then its not wort the trouble strippng the boiler down to fit a new one, it is easier to fit a remote vessel somewhere on the system, but this will need to be sized accordingly. The fan is a seperate issue, a lot of them squeek a bit on start up you can get a purpose made lubricant for them from places like parts centre, dont just squirt it with WD40 as ive seen done it needs to be a lubricant that works at temperatue.
    Just out of interest is it the old 28CDi or is it the Greenstar?
     
  10. GC17

    GC17 New Member

    Yes it's a 28CDi.

    I think this problem started a couple of months ago. We refitted a radiator which had been off for replastering and obviously the pressure dropped in the system. Stupidly I didn't repressurise immediately and after dinner turned on the hot water to do the washing up. As the pressure in the boiler was significantly below 1 bar no hot water appeared and when I went upstairs to the boiler (a matter of minutes later) it smelt slightly of burning and a red light was flashing (domestic water demand indicator - this indicates an air flow fault from what I understand from the user manual). The appliance re-lit after the appropriate waiting time and appeared to be ok after we repressurised back up to over 1 bar.

    At the time we were only using the boiler for hot water but I noticed that it was dropping pressure slowly. Also this air flow fault kept happening intermittently when we used the boiler for hot water. We diagnosed that the the automatic air vent at the top of the boiler had been totally closed when in fact it is supposed to be very slightly open on the 28CDi. Since opening it a little we've had no further air flow faults. However - the dropping pressure problem HAS continued and this is now significant since the CH has been turned on.

    So.....would what happened that day (boiler overheating with insufficient water pressure) have caused this expansion vessel fault? If so is it likely that the expansion vessel needs repressurising or do you think we need a new fan AND expansion vessel :(

    Thanks!
     
  11. GC17

    GC17 New Member

    p.s. how do we isolate the boiler from the heating circuit?
     
  12. GC17

    GC17 New Member

    oh dear - I realise now that you isolate the flow and return valves as they enter the boiler. Unfortunately we didn't do that and thought isolating the filling loop was isolating the boiler. We then took boiler pressure down to 0 using pressure release valve. We pumped some air into the expansion vessel (using foot pump)which showed on the pressure gauge at 0.5 bar. Concerned something was wrong we released this pressure with the pressure release valve, reset to 0 then filled with water to 1.5bar. Heating came on but we got the air flow fault....and pressure started dropping..... Unfortunately now whenever we try to refill the boiler the water is going straight to the discharge and the boiler pressure is remaining at 0. Have we damaged the seal on the expansion vessel beyond repair? Time to get a plumber out to replace that??? Seems to me this is a time consuming and costly job on the 28CDi - would we be best to request a remote vessel? Any idea of what this should cost us so we don't get stung big time?

    OR do you think the pressure release valve isn't sealing properly now??

    Thanks again for all your help.
     
  13. GC17

    GC17 New Member

    Quick update - Turns out the pressure release valve was stuck. Seems to have clicked back into position now :) Now boiler is maintaining pressure when off again - phew.

    Testing the expansion vessel under pressure (at least 1 bar) by pressing the schraeder valve didn't release any water - from what I understand this means the expansion vessel just needs recharging? (we didn't hear any air released either tho).

    We're being quoted £150 to recharge expansion vessel and replace PRV - £350 to replace expansion vessel too!!! Seems to me that we can recharge expansion vessel ourselves but are nervous about turning off flow and return valves as we've read that these can leak because they aren't used often? Is this absolutely necessary? Also - what's the best way to drain the boiler as we really don't want to touch the PRV again!
     
  14. Soooo many Qs... :).

    Chill, man.

    cough

    Ok. With your system at pressure (whatever pressure it's at), if you pressed the wee tip of the Shrader valve on the expansion vessel and no air and no water came out, that's good news.

    No air coming out means that it needs recharging, so that could well be the cause of yer problems. No water coming out means the rubber membrane inside ain't ruptured, so that's also good news as your vessel should be fine.

    So, to recharge it:

    Turn off the boiler. No need to isolate the flow & return to the boiler as there's another way; open a rad bleed screw and bleed. Lots. Until no more water comes out. That will take a while. If you prefer, slacken a rad valve and hold a pan under it...

    (You could drain the system by manually opening the pressure release valve, but as I hope you've now gathered, it's best not to touch that fellow as they are sensitive (like me) and likely to dribble afterwards (er, like, er, y'know... :oops: )

    So, get the system pressure to zero - ie: no more water coming out. Now pressurise the expansion vessel with air to 1 bar using a foot/hand pump. Use a gauge - do it properly.

    Then re-pressurise the water side to also 1 bar, or up to 1.2 bar. That's enough pressure - chust no need to go higher.

    Job done.

    Keep an eye on the discharge pipe - it might well continue to dribble, 'cos they are poor at resealing once opened.

    If it does still dribble, there's a few options. One is to try re-seating it. To do this, manually open it and allow it to slam shut firmly. Do this a few times. It might work, or it might not.

    If that fails, you have two further options; if it's a tiny drip, you can live with it. Eg, if it takes a couple of months for the pressure drops to, say, 0.5bar before needing re-topping. Bear in mind, tho', that renewed fresh water will introduce air each time so that could lead to internal corrosion.

    Or, have it replaced. The part is around £25-£30, I think, and is an easy half-hour job. Should be under £100 all in. I think.

    Your vessel sounds as tho' it's fine, but if you do need to replace that, come back on here and ask - it's an easy DIY job.
     
  15. Dave does Gas

    Dave does Gas Screwfix Select

    Quickest way to take the pressure off you system without isolating the boiler is to use the system drain off point and a hose, attach the hose 8mm spanner open the drain off cock and realease the pressure, have someone by the guage give you a shout when it hits zero turn off the DoC and re pressurise the expansion vessel. Refill the system to 1.5 bar and jods a good one.

    Little tip for the future NEVER and I mean NEVER use the PRV as a means to release presure or drain the boiler, it is a safety device and not designed as a drain off. The times Ive had to change them because people find it the easy way to drain a boiler are beyond belief.

    If you do need a new vessel, then if it was me I would be pushing you to fit a remote one, Ive done those old Worcesters in the past and there not exactly service / maintenance friendly. The Vessel itsself would cost in the region of £100.00 ish dependant upon the size of your system. I cant give you a labour price as it will depend on where you are but two to three hour job at the most. Allow for the cost of replacing inhibitor as well.
     
  16. The DoC! I always forget about that fellow, 'cos I don't have one... :(
     
  17. plumberboy

    plumberboy Well-Known Member

    You don't have one DA!!! Who installed such a system.:rolleyes:
     
  18. plumberboy

    plumberboy Well-Known Member

    Sorry DA,I couldn't help myself.:(
    I'll go and sit in the corner and think about my actions.
     
  19. GC17

    GC17 New Member

    Yep - apologies for that - we did panic a little! Plan to take off a rad tonight to release the pressure in the boiler. Little wary of using the drain off point just incase we can't shut it off again and then it will drain the entire system...... (And yep - learnt the PRV thing the hard way! Tho think it needed replacing anyways as has deffo had slow leak for a good few months now - and is now dropping about 0.2 bar a day - bugger! Looks like the part is about a tenner tho and a job we could do ourselves???)

    But first things first! Surely if we are recharging the expansion vessel the increase in air pressure in here will push water back into the boiler and increase the pressure in the boiler again (which I'm guessing is what we saw happen on Saturday night). So are we right in thinking that we need to keep the bleed valve open to make sure that extra water pressure doesn't raise the pressure in the boiler again? (we thought taking off one of the big rads, emptying and putting back on again would probably drop the pressure enough and give us some extra to play with?) From what I understand there might be a signifcant amount of water in the expansion vessel that needs displacing now?

    Thanks again for all your help - VERY much appreciated. Especially explaining everything in such a simple way :)
     

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