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Leaking PRV/ boiler pressure dropping

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Leaking PRV/ boiler pressure dropping

Postby Jimmy Mack » 21 Jan 2018, 11:50

We have a Glowworm 30 sxi combi condensing boiler / closed central heating system.

The PRV overflow discharge was leaking, we were losing pressure and the system would shutdown due to low pressure.

I tried a few tricks with the PRV, flicking the release to dislodge any debris, disassembling the valve...to finally replacing with a new valve unit.

This morning we woke to no heating and frustratingly the new PRV has drip, drip ...released all the system pressure.

Among other things I've tried are, dropping the user rad temp dial on the boiler, and reducing the system pressure when cold to around 1.0 - 1.2 bar.

A sepertate job this week was unblocking a 2m section of 15mm plastic CH pipe as two rads weren't heating at the end of the system...I blame those little inserts at the joints, for reducing the bore.

TBH, as well as not being qualified it's a little beyond me so it's probably time to call a plumber, though I was hoping to ride it out till the spring.

Anything I might be missing? Is the leaking PRV pointing to something else?

Jim


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Re: Leaking PRV/ boiler pressure dropping

Postby 9fingers » 21 Jan 2018, 12:38

In normal use the PRV should just sit there and never operate unless there is an over pressure problem.
I suspect that the new one is operating regularly and hence has got some crud under the valve seat especially if you have been disturbing muck in the system elsewhere.

The question is why is it operating regularly. I would suspect that the expansion chamber diaphragm has failed. This may be integrated into the boiler which makes it bespoke, expensive and a pain to get to BUT it is perfectly permissible to insert a new common one anywhere on the circuit that you can hide a 1 cu ft lump and just leave the defective one where it is.

Fitting one is not difficult and they can be sourced on ebay.

HTH

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Re: Leaking PRV/ boiler pressure dropping

Postby Jimmy Mack » 21 Jan 2018, 12:54

9fingers wrote:In normal use the PRV should just sit there and never operate unless there is an over pressure problem.
I suspect that the new one is operating regularly and hence has got some crud under the valve seat especially if you have been disturbing muck in the system elsewhere.

The question is why is it operating regularly. I would suspect that the expansion chamber diaphragm has failed. This may be integrated into the boiler which makes it bespoke, expensive and a pain to get to BUT it is perfectly permissible to insert a new common one anywhere on the circuit that you can hide a 1 cu ft lump and just leave the defective one where it is.

Fitting one is not difficult and they can be sourced on ebay.

HTH

Bob
I've tickled the new PRV to clear any potential gunk... At present the discharge pipe outside isn't dripping.

We've an expansion vessel, as you say, next to the boiler, and there's another (bespoke) one inside the boiler.

I've tried to look for info on the pressure of the external vessel... should it match the system cold pressure? Say 1.5bar?

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Re: Leaking PRV/ boiler pressure dropping

Postby 9fingers » 21 Jan 2018, 12:58

I've just consulted the manual here https://www.glow-worm.co.uk/glow-worm/s ... 157235.pdf
and see that it does indeed have an integral expansion chamber.
There is no mention of a pressure test point on the dry side of the expansion vessel. This is usually a schrader valve (as per normal car tyre). A common indication of a failed diaphragm is that when the centre pip is depressed, water not air comes out.
With the heating side at zero pressure, the pressure at the schrader valve should be 0.5 bar or 7PSI

hth
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Re: Leaking PRV/ boiler pressure dropping

Postby 9fingers » 21 Jan 2018, 13:05

OK so why two expansion chambers?
Either the internal one failed a while back and an external one has been fitted and now it too has failed??

The manual for the boiler says the EV should be pressurised to 0.5 bar so I'd follow that for the other one too but it must be set when the circuit pressure is zero. Try releasing the valve on the external one (if it is at the bottom as installed) and see if water comes out.

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Re: Leaking PRV/ boiler pressure dropping

Postby Jimmy Mack » 21 Jan 2018, 13:06

That does help Bob, the expansion vessel (external) is at 1.5bar... Perhaps too high. I've depressed the valve here to drop the pressure... No water discharge, a good sign.

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Re: Leaking PRV/ boiler pressure dropping

Postby RogerS » 21 Jan 2018, 13:11

Jimmy Mack wrote:...
A sepertate job this week was unblocking a 2m section of 15mm plastic CH pipe as two rads weren't heating at the end of the system...I blame those little inserts at the joints, for reducing the bore.
...


Definitely NOT the inserts reducing the bore. If they did then no-one would be buying the stuff as it would have such a bad reputation. besides...think 28mm or 22mm or 15mm or 10mm...heating systems work with all sorts of pipe sizes (unless it's mine :( ). Was it an air lock or black gunk? The early plastic pipes would block up if there was no water circulation.
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Re: Leaking PRV/ boiler pressure dropping

Postby 9fingers » 21 Jan 2018, 13:26

Jimmy Mack wrote:That does help Bob, the expansion vessel (external) is at 1.5bar... Perhaps too high. I've depressed the valve here to drop the pressure... No water discharge, a good sign.

Thanks

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Yes indeed a good sign! Why are you setting the cold pressure so high. Manual says 0.7 bar minimum so no more than 1 bar needed surely.
Is the PRV calibrated? I think they are normally set to 3Bar? However being newish we can assume it is OK (?)

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Re: Leaking PRV/ boiler pressure dropping

Postby 9fingers » 21 Jan 2018, 13:29

Although technically forbidden. I keep my system fed from a pressure regulated supply of 1bar and non return valve.
But don't tell anyone :lol:

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Re: Leaking PRV/ boiler pressure dropping

Postby Jimmy Mack » 21 Jan 2018, 13:33

You're right Roger... This is what I said to a British gas chap who suggested all the plastic (Barrier type!) should be removed and replaced with copper, as the plastic causes air ingress and corrosion issues... Etc etc.. He came back with a massive quote. Ironically the Hep2O stuff is endorsed by British Gas!

The blockage was magnate, I believe, it felt like compacted sand when I pushed a coat hanger into it. So I cut it out, cleaned and refitted.

When we first moved in a lot of the rads were isolated, some at both the trv and lock shield return! So indeed the lack of circulation was probably the problem. We have a magna-clean which needs a good clean out every year.

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Re: Leaking PRV/ boiler pressure dropping

Postby Jimmy Mack » 21 Jan 2018, 13:43

9fingers wrote:
Jimmy Mack wrote:That does help Bob, the expansion vessel (external) is at 1.5bar... Perhaps too high. I've depressed the valve here to drop the pressure... No water discharge, a good sign.

Thanks

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Yes indeed a good sign! Why are you setting the cold pressure so high. Manual says 0.7 bar minimum so no more than 1 bar needed surely.
Is the PRV calibrated? I think they are normally set to 3Bar? However being newish we can assume it is OK (?)

Bob
The PRV is rated 3.0 bar. I've dropped the cold pressure right down now... I'm sure I read it was between 1.2-1.5 . This might of been a doctor Google fail.

I'll keep an eye on how it performs at a lower pressure and with the pressure of the vessel now at 0.5. I released the system pressure to do this, though I'm not 100% confident in the gauge accuracy of my foot pump.

This may explain the additional vessel...

From the manual

NOTE: The expansion vessel volume depends on the total
water system volume and the initial system design pressure. To
check if an additional expansion vessel is required, an accurate
calculation of vessel size is given in the current issue of BS5449
and BS7074 Part 1, for IE refer to the current edition of I.S.813
"Domestic Gas Installations".

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Re: Leaking PRV/ boiler pressure dropping

Postby 9fingers » 21 Jan 2018, 13:52

OK Fingers crossed then.

Keep any eye on the system pressure when hot. Should not be going anywhere near 3 bar unless the system volume is to high for the size of EV fitted.

Is the system relatively new? any history of problems apart from the PRV you mentioned?

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Re: Leaking PRV/ boiler pressure dropping

Postby Jimmy Mack » 21 Jan 2018, 14:20

The boiler is 12+ years old, installed by the previous owners. (There's an inhibitor installation sticker clue dating back to 2006) The only issues we've had are blockages on two legs of the system... Of which after three years of tinkering I've managed to sort by finding the offending section with a cut, clean and re- fit of the pipe work.

It's an unusual layout, with some poor jointing /routing (see pic from the last unblock). I've only managed to map out about 80% of the system route, I think the last two rads I freed up are plumbed in series! There are a few parts of the system fighting over flow and I've spent some time balancing rads.

It's a classic case of a system that's been added to over the years and nobody really knew what was going on - the house is an unusual layout which doesn't help, and neither does the hardboard layed under the carpets!

Image

Detail pic bottom left of rad

Image

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Re: Leaking PRV/ boiler pressure dropping

Postby 9fingers » 21 Jan 2018, 15:29

Well it could just be the extra volume of water that you are now able to heat having unblocked those rads is taking you over the capacity of the EV. But don't panic as the pressure adjustments might well have done the trick.

Fingers crossed for you

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Re: Leaking PRV/ boiler pressure dropping

Postby RogerS » 21 Jan 2018, 15:31

Jimmy Mack wrote:You're right Roger... This is what I said to a British gas chap who suggested all the plastic (Barrier type!) should be removed and replaced with copper, as the plastic causes air ingress and corrosion issues... Etc etc.. He came back with a massive quote. Ironically the Hep2O stuff is endorsed by British Gas!

The blockage was magnate, I believe, it felt like compacted sand when I pushed a coat hanger into it. So I cut it out, cleaned and refitted.

When we first moved in a lot of the rads were isolated, some at both the trv and lock shield return! So indeed the lack of circulation was probably the problem. We have a magna-clean which needs a good clean out every year.

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Yes they really cocked up with the first generation of pipe. I never got a reply from them when I complained...I wonder why. It works fine while there is circulation but if you switch off a few rooms then that magnate drops out of solution (or seems to) and ONLY in the plastic pipe which is bizarre. A long length of mixed plastic and copper showed only the plastic to be blocked! Power-flushing fails to shift it because it relies on at least some throughput to work.

Modern plastic pipe is 'barrier' pipe and doesn't have the same problems.
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Re: Leaking PRV/ boiler pressure dropping

Postby RogerS » 21 Jan 2018, 15:34

Ha ha...looking at that last photo looks as if someone didn't understand mains bonding requirements !
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Re: Leaking PRV/ boiler pressure dropping

Postby Jimmy Mack » 25 Jan 2018, 20:34

RogerS wrote:Ha ha...looking at that last photo looks as if someone didn't understand mains bonding requirements !
I got my qualified buddy to check the electrics before we moved in... He noticed the bonding wasn't connected to the main earth!.... The whole house wasn't earthed! He corrected it and also connected the "bypassed' electric shower to the correct RCD which "quelle suprise' subsequently highlighted a problem with the shower appliance... At this point the homeowner actually turffed him out and said he broke the shower... Their conveyancing solicitor sent a snotty letter.

Would you believe it...? A faulty shower, no earth....! They should of sent him a thank you card and a case of beer!

Cheeky ****er's!


In other news my system is still leaking... So I removed the external panel of the boiler to check the built in custom expansion vessels (naughty)... And Bob, would you believe it, it's full of water!... I'd have a go, but I think considering it's in the boiler, now is the time to call in a professional.... And probably an expensive part unless he or she up's the size of the extension vessel.

Unfortunately I don't know any heating engineers.... Russian roulette time with the gas Safe register I guess unless anyone knows one in Leeds?

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Re: Leaking PRV/ boiler pressure dropping

Postby 9fingers » 25 Jan 2018, 20:45

Most people leave the defective internal EV inside the boiler due to the cost of the new part and the possible complexity of the fitting.
I don't believe that you know why there is an external vessel fitted. It maybe that a previous owner solved the problem in the "normal" way by adding an external EV. That could be undersized now that your system has sprouted extra rads perhaps fitted after the EV was sized.

There are bound to be online estimators for EV size. I would use one of those to see how much margin you have with your current EV and then decide what to do.

hth

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Re: Leaking PRV/ boiler pressure dropping

Postby Jimmy Mack » 25 Jan 2018, 21:03

9fingers wrote:Most people leave the defective internal EV inside the boiler due to the cost of the new part and the possible complexity of the fitting.
I don't believe that you know why there is an external vessel fitted. It maybe that a previous owner solved the problem in the "normal" way by adding an external EV. That could be undersized now that your system has sprouted extra rads perhaps fitted after the EV was sized.

There are bound to be online estimators for EV size. I would use one of those to see how much margin you have with your current EV and then decide what to do.

hth

Bob
Ah!... That's a good bit of sideways thinking Bob...I hadn't considered that external EV was potentially a remedy to a failed int EV, I just assumed it to be that the system was too large for the int alone.

I'll see if I can find a calculator. We have 13 rads!

Thanks.

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Re: Leaking PRV/ boiler pressure dropping

Postby 9fingers » 25 Jan 2018, 21:07

NB
Coefficient of thermal expansion of water 0.000214 per degree C
So taking extreme values of heating from 0 to 100C (neither of which is realistic but makes the sums easier) the expansion will be 2.14%

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Re: Leaking PRV/ boiler pressure dropping

Postby MJ80 » 25 Jan 2018, 22:24

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Re: Leaking PRV/ boiler pressure dropping

Postby RogerS » 26 Jan 2018, 09:28

I'm toying with the idea of adding an expansion vessel to our hot water pump. Currently the house has three expansion vessels in the cellar. One for the well pump. Another for the cold water pump and the third for the backwash pump. One of the advantages is that the duty cycle on the pump is lengthened.

At the moment, the hot water Stuart Turner pump has a tiddly little expansion vessel and so almost as soon as you turn any HW tap on the pump starts. When SWMBO does the dishwashing, she is always momentarily turning on the HW tap which starts the pump. But only for a few seconds. The constant on/off is driving me nuts and I'm sure it's not doing the pump any good. So I propose to give Stuart Turner a call to see if I can add a larger expansion vessel.

I Googled 'Calculating expansion vessel size' and that gave a lot of hits and formulae.
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Re: Leaking PRV/ boiler pressure dropping

Postby 9fingers » 26 Jan 2018, 10:00

ST will possibly have a different name for it as it is not dealing with expansion but I don't know the name. However they are essentially the same device.
Make sure you get one designed for potable water. They are usually blue or white not the red ones I sent you links too a while back. They will be a bit dearer as they use stainless steel.
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Re: Leaking PRV/ boiler pressure dropping

Postby RogerS » 26 Jan 2018, 10:52

Thanks for the heads-up re a potable vessel. Hadn't realised the difference. ST say not a problem, Only drawback is that if the water's not used then the heat is lost..so have to wait longer. But in my scenario, don't think that will be a problem. Food for thought.
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Re: Leaking PRV/ boiler pressure dropping

Postby 9fingers » 26 Jan 2018, 10:59

RogerS wrote:Thanks for the heads-up re a potable vessel. Hadn't realised the difference. ST say not a problem, Only drawback is that if the water's not used then the heat is lost..so have to wait longer. But in my scenario, don't think that will be a problem. Food for thought.


Heat loss would be occurring the same as in your pipe runs and I can't see why you should not lag the vessel but not the pump.

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