Boiler losing pressure

[pluckedfumbingSE9]

Hi,

I have a worcester bosch (24CDi) boiler. i top it up to 1-1.5 bar when cold then heating goes on, spanks up to 3.5 bar, pressure release valve goes (as it should, it's set to 3 bar), then pressure steadily drops over next week or so. The pressure release valve appears not to keep on dripping once it gets back below 2.5 bar or so. It seems from other posts that my problem could be something to do with the expansion vessel, but it seems to be a completely sealed unit so no idea how I would check this. Does anyone have any idea how I could sort out this problem?

Thanks

 

[nickso]

read the FAQ's on expansion vessels.

the valve to repressurise on cdi's is on the front of the vessel, you cant miss it.

 

[pluckedfumbingSE9]

OK cool, thanks. So by the looks of it I need a bike pump and some way to drain the system. There is a big old tap under the kitchen radiator with an end of pipe protruding beyond the end of it - anyone have any idea if this is how I would drain it before re-pressurising (assuming it does not need to be replaced)?

Thanks

 

[nickso]

cdi's have drain cocks on them. they may be more reliable than a system draincock

if its still there remove the white panel underneath the boiler (pulls off from front edge) there are two white nuts with small spouts under them, one on each side of the boiler. they quite often get blocked up but the right side one usually works better than the left one. unscrew anticlockwise with a bucket or something underneath to catch the water. be gentle with anything plastic on cdi's, the yellow manifold plastic can go brittle with age. if nothing comes out of either boiler draincock then you may have to use your system draincock.

leave the draincock open while you pump the vessel, expect lots more water to come out as you do so. i repressure to 1 bar, some do less.

 

[pluckedfumbingSE9]

Thanks very much indeed for your help Nickso, I will give that a pop this evening. Should unscrewing those nuts drain the system right down to 0 bar plus the 'additional 10 litres or so' recommended by the FAQs? I guess to an extent it will depend on the size of the PV and how b ggered it is, will it?

Thanks again, that's really helpful.

 

[nickso]

yes, unscrewing either of those drains will put it right down to zero, be sure not to get a wet sleeve whilst undoing the first one, i put a small tube on the spout to save getting wet, you will see what i mean when you look at it.

the water will stop after a while, as you pump the vessel more water will come out so leave your bucket in place. you probably have zero vessel pressure so will get a fair amount of water out.

 

[pluckedfumbingSE9]

Thanks again. last questions now, I promise.

1) I guess the system has to have been off for a while and has to be cool?

2) I can't find a pump with a pressure gauge. I suppose there is no way of doing it without being able to accurately measure the pressure though, is there? maybe I can find a hand-held gauge somewhere

3) is this safe for me to do myself?

Thanks once more

 

[nickso]

Thanks again. last questions now, I promise.

1) I guess the system has to have been off for a while and has to be cool?

2) I can't find a pump with a pressure gauge. I suppose there is no way of doing it without being able to accurately measure the pressure though, is there? maybe I can find a hand-held gauge somewhere

3) is this safe for me to do myself?

Thanks once more

1) ideally yes but not essential.

2)you need a pump with a gauge

3)yes, you are not doing anything risky, obviously turn off the electrics and dont be a thoughtless muppet when you are doing it if you dont feel confident then call someone in, better to have spent a little bit of money on a professional than make a balls of it, only you know if you will manage.

 

[pluckedfumbingSE9]

Hey nickso,

thanks very much for your help. Pumped it up and it worked a treat - only thing i was not sure about was how to be sure I had pumped out enough water. I basically kept on pumping until the guage went up to 1 bar then closed the release valve again - but I guess that this could actually mean that I did not get enough water out of the system, couldn't it? Either way, the pressure is still dropping - much more slowly, but it's definitely going down. Did I do something wrong? There is no leak as far as I can tell and no water came out of the air valve which indicates that the diaphragm has not been pierced. Do PVs sometimes just leak or should i have waited until ten litres came out of the system (as per the FAQ) before pumping it back up and closing the water escape valve?

Thanks again for your help

Nick

 

[Madmog]

We had a similar problem with our combi boiler last year. It turned out there was a small hole in the expansion vessel (which we had replaced and solved problem). The problem got worse over the weeks, so I advise to get it looked at ASAP.

 

[Madmog]

We had a similar problem with our combi boiler last year. It turned out there was a small hole in the expansion vessel (which we had replaced and solved problem). The problem got worse over the weeks, so I advise to get it looked at ASAP.

 

[pluckedfumbingSE9]

how did you detect the hole? and how much did it cost to get a new PV put in there if you don't mind me asking? There is no obvious hole in ours but i iwll have a look at as much of it as I can see when I get home...

 

[shambolic]

Check the shraeder valve on the expansion valve is not leaking air (use a bit of soap solution) Also check PRV outside as it may have a dirty seating allowing water to leak outside (as it will have been opening at 3 bar due to empty exp vessel)

 

[pluckedfumbingSE9]

Thanks Shambolic,

water not leaking out of the PRV as far as I can tell, though you are right that it did open when the vessel was empty (it was pretty scary watching the pressure get up to close to boom point!). i will check to see if the valve is leaking. I guess it is conceivable that I just didn't chuck enough air in to the system - what I don;t really understand is how the pressure on the pressure gauge (and on my pump) was giving a meaningful reading if the water release valve was open, thereby not giving it anything to push against. Am I being an idiot? how do I know what the true air pressure inside my PV is?

Thanks again

 

[Agile]

Yes about the idiot!

The air is held in a runner bag which presses against the outside of the expansion vessel!

You check the PRV vent for leaking by putting a bottle or bag over it and leave for a day.

Tony