Central Heating Pressure Vessel - Faulty or just 'gone flat'

[Angelchops]

I'd appreciate some advice regarding the pressure vessel on my heating system. We have a regular Worcester Bosch 24ri boiler, not a combi and there is an external pressure vessel fitted.

Like most people I bleed all of our radiators once a year at about this time which is what I did the other week. Afterwards I used the filling loop to top up and take up the cold pressure to 1 bar as I always do. This time when I turned everything back on the pressure rose to 2bar but unlike previous year carried on climbing to 3bar then vented outside via the pressure relief valve.

I turned everything off and it fell to zero on the gauge, so then I turned it on again without re-filling. It climbed to just under 2bar ie it's normal running pressure, stopped rising and everything ran normally with all radiators working fine. It has continued to do so for over a week now with no apparent issues.

I researched the high pressure issue and assumed the diaphragm in the vessel had failed. To confirm this I depressed the schrader valve expecting water to appear - no water came out but neither did any air. I had a go at pumping it up at this point, after opening a bleed valve on an upstairs radiator to allow 'room'. The gauge on my pump showed a healthy pressure whilst connected to the vessel but didn't seem to need much pumping to reach this. Then each time as I removed the connector I lost the pressure. Depressing the schrader valve afterwards gave the tiniest 'phut' noise, so clearly nothing was going in.

So my questions...
- Am I OK for now running everything as it stands ie from zero cold pressure rising to just under 2bar when hot or is there likely to a long term issue doing this. I can't get our regular gas engineer out for a couple of weeks at least what with half term etc.
- What could be the problem with the pressure vessel if anything? There certainly doesn't seem to be water in the 'air side' so could it be something as simple as a faulty schrader valve? Any ideas welcome.

Many thanks everyone.

 

[Deleted member 267285]

If you have an unvented cylinder, then this should only be worked on by a G3 registered engineer. If it’s a sealed system, you may be ok. You may have a blockage in the communication pipe/hose, or you might not be pressurising it correctly.

 

[Angelchops]

If you have an unvented cylinder, then this should only be worked on by a G3 registered engineer. If it’s a sealed system, you may be ok. You may have a blockage in the communication pipe/hose, or you might not be pressurising it correctly.

Thanks for your thoughts Chris, it's a regular cylinder with a header tank not unvented, should have mentioned this, I realise they're a no-no for DIY.

 

[ianmcd]

I researched the high pressure issue and assumed the diaphragm in the vessel had failed

Research again and you will find that your vessel should be checked re-charged properly every 12 months, you havent re-charged it correctly, there are hundreds of posts on here telling you how to do it correctly, follow ALL the steps not just the ones you like

 

[Angelchops]

Research again and you will find that your vessel should be checked re-charged properly every 12 months, you havent re-charged it correctly, there are hundreds of posts on here telling you how to do it correctly, follow ALL the steps not just the ones you like

Oh dear. There's no need for patronising Ian - a little politeness and courtesy costs nothing.
Anyway, I do get my boiler serviced regularly but I know for a fact he never looks at the expansion vessel. I must make sure he does so in future.
I did research this for over an hour yesterday but clearly didn't find the 'right' set of instructions. Could you point me towards the best of the hundreds of posts on here please? I'd be very grateful.

 

[ianmcd]

I wasnt being patronising, I am fed up with the amount of so called service engineers that supposedly service a boiler, they dont, they poke and go and take your money after doing the square root of nothing, to properly re-charge your EV you have to de-pressurise the system, you MUST leave a drain point open, as you start pumping all the excess water that is held inside the EV will now be expelled, once the water stops running, now you are charging the vessel , pump it to 0.8 Bar, then close the drain point and re-fill the system, no drain point left open during the whole operation, no point in doing anything

 

[Angelchops]

Thanks Ian no worries. That's pretty much exactly what I did. I removed completely the bleed valve on one of my upstairs radiators.

I live in a three storey house and have wondered since whether it would have been more effective using the radiator closest to the expansion vessel which has coincidently has the main drain off cock? I also read on one set of instructions which suggested turning the pressure release valve head and holding it open while pumping, but thought that could damage the valve so decided not go down that road.

Anyway, I'll try again tomorrow, if that fails I'll wait for my gas engineer to reappear from his holidays - I'd better ask him why he didn't check the pressure at the last service too!

 

[ianmcd]

which has coincidently has the main drain off cock?

Why not just open the drain off cock ? dont use the PRV that is a bad idea

 

[Angelchops]

Why not just open the drain off cock ? dont use the PRV that is a bad idea

Yes, that's exactly my thoughts. I'll give it a go.

 

[ianmcd]

when the drain point stops running, attach the pump to the EV and start pumping, make sure that the surplus water is now dispelled, if it isnt the communication hose/pipe is blocked and that is your problem, you should get a fair bit of water coming out once you start pumping

 

[Angelchops]

Thanks Ian.

 

[Angelchops]

when the drain point stops running, attach the pump to the EV and start pumping, make sure that the surplus water is now dispelled, if it isnt the communication hose/pipe is blocked and that is your problem, you should get a fair bit of water coming out once you start pumping

Thanks Ian. I think I was reluctant to open that downstairs drain cock because I'd imagined it would drain down the entire system, but as I'm reading more on the subject, I'm now realising it can't drain down unless the bleed valves are all open upstairs. However... can I just check my understanding is correct on that particular point?

Read more: https://www.diynot.com/diy/threads/...aulty-or-just-gone-flat.579961/#ixzz7AEaxAARr

 

[ianmcd]

yes the upstairs rads will hold as long as you dont open the bleed vaves

 

[Angelchops]

yes the upstairs rads will hold as long as you dont open the bleed vaves

Hi Ian, I went ahead as planned yesterday and followed all of the steps we discussed here, but with no success. Despite having that drain off valve fully open it was still like I'm pumping against a brick wall. Any pressure I build up seems to be in the pump itself not in the vessel. I even removed the Schrader valve to see if the extra force would help free thing up, but the symptoms were the same. So I conclude there is a blockage somewhere or the vessel itself is no longer serviceable. It's probably as a result of neglect ie not being checked/pumped up when the boiler has been serviced over the years. Something I'm now wise to thanks to you and will insist is done in future. I think I've now reached the limit of my patience with it and will get an engineer in. Ah well, c'est la vie. Thanks again for your help and advice.

Interestingly there is an entertaining video on you tube of a guy freeing off a very large pressure vessel, probably not central heating, but with a similar issue. The vessel seems to be removed and in his yard outside. He had it connected to a large 'garage style' compressor pump and was heating it with a blow lamp and simultaneously hitting the area around the valve with a hammer and then pushing an Allen key through the valve hole with the core removed ! I can only presume the rubber balloon / diaphragm had stuck to the inside of the vessel and this was to detach it? It looked pretty dangerous to me but perhaps predictably he succeeded in the end. Clearly, not something for a DIYer to try at home!

 

[Gasguru]

Stick a new vessel on and get a new service eng.