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08-12-2010, 15:47   #1
MuffinsDa
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Immediate Loss of Pressure in Sealed / Pressurized Central Heating System

We have moved into our current home a few months ago. It's a very old house with relatively haphazard plumbing. Things worked fine until recently when I noticed that the pressure in the sealed system is on 0.5bar and it's not heating the upstairs radiators.

Got a plumber that had done some work on this house before, and he said there was no filling loop, he connected a pipe in the attic to connect mains system to the sealed system and repressurized it.

Looked ok for a couple of days but the system completely failed yesterday, and now when you repressurize it it goes back to zero bar almost immediately (as soon as you close the filling loop).

Plumber says this is definitely due to a leak. I find it a bit strange though, as: a) It has to be an absolutely huge leak if it looses that much pressure instantly, and b)there was no problem with the system and it wasn't losing any pressure (steady at 0.5bar) until he fiddled with it!

Based on that, can anyone think of anything that your man had done to screw it up, or is it really a leak that coincidentally appeared after he did the work a couple of days ago?

There are no signs of leaks anywhere in the house btw, he thinks it's downstairs and wants to dig up the floors!

Any advice would be greatly welcome. Not the best time of year to be left without central heating!
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08-12-2010, 15:55   #2
antiskeptic
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Originally Posted by MuffinsDa View Post
We have moved into our current home a few months ago. It's a very old house with relatively haphazard plumbing. Things worked fine until recently when I noticed that the pressure in the sealed system is on 0.5bar and it's not heating the upstairs radiators.

Got a plumber that had done some work on this house before, and he said there was no filling loop, he connected a pipe in the attic to connect mains system to the sealed system and repressurized it.

Looked ok for a couple of days but the system completely failed yesterday, and now when you repressurize it it goes back to zero bar almost immediately (as soon as you close the filling loop).

Plumber says this is definitely due to a leak. I find it a bit strange though, as: a) It has to be an absolutely huge leak if it looses that much pressure instantly, and b)there was no problem with the system and it wasn't losing any pressure (steady at 0.5bar) until he fiddled with it!

Based on that, can anyone think of anything that your man had done to screw it up, or is it really a leak that coincidentally appeared after he did the work a couple of days ago?

There are no signs of leaks anywhere in the house btw, he thinks it's downstairs and wants to dig up the floors!

Any advice would be greatly welcome. Not the best time of year to be left without central heating!
It would appear you've a leak okay. Have you wooden floors downstairs - if so and there's a void then you can lose water through a split pipe without detecting it above ground. Or is there a pressure relief valve in the system (which usually drain to outside). If stuck open (which could happen if the fill loop isn't fully sealing and overpressurized the system) then you'd lose water quickly but should see it draining from a pipe poking out the wall outside somewhere.

Then there's the boiler itself - where is it located and is there water pouring out of it?
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08-12-2010, 16:02   #3
MuffinsDa
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It would appear you've a leak okay. Have you wooden floors downstairs - if so and there's a void then you can lose water through a split pipe without detecting it above ground. Or is there a pressure relief valve in the system (which usually drain to outside). If stuck open (which could happen if the fill loop isn't fully sealing and overpressurized the system) then you'd lose water quickly but should see it draining from a pipe poking out the wall outside somewhere.

Then there's the boiler itself - where is it located and is there water pouring out of it?
Thanks for getting back to me, I appreciate your advice greatly! Freezing here as I type!

Yes its wooden floors downstairs and there is a void, so that can be a possibility.

PRV is located next to the boiler and it's not letting water out, neither is the bolier. They are both located at a small boiler house in a courtyard outside the house and there doesn't appear to be any water coming out of them.

But am I not correct that for the pressure to drop that quickly (from 1.5bar to 0 in 30 seconds!) there needs to be a major leak, and it should be possible to hear something?

Can it be something to do with the expansion vessel (no visible leaks there), coils, or anything similar?

Also when he connected the mains to CH he used a normal (twisty type) valve, is that ok? Last house I was in it was a different type.
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08-12-2010, 17:00   #4
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The valve doesn't matter. It'll be a fairly substantial leak alright, if it allows to pressurize up to 1.5 bar and takes 30 seconds to dissipate. Difficult to suggest how to fault find without looking at the system.

What work did the plumber actually do when he was there last?
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08-12-2010, 17:38   #5
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Originally Posted by MuffinsDa View Post
We have moved into our current home a few months ago. It's a very old house with relatively haphazard plumbing. Things worked fine until recently when I noticed that the pressure in the sealed system is on 0.5bar and it's not heating the upstairs radiators.

Got a plumber that had done some work on this house before, and he said there was no filling loop, he connected a pipe in the attic to connect mains system to the sealed system and repressurized it.

Looked ok for a couple of days but the system completely failed yesterday, and now when you repressurize it it goes back to zero bar almost immediately (as soon as you close the filling loop).

Plumber says this is definitely due to a leak. I find it a bit strange though, as: a) It has to be an absolutely huge leak if it looses that much pressure instantly, and b)there was no problem with the system and it wasn't losing any pressure (steady at 0.5bar) until he fiddled with it!

Based on that, can anyone think of anything that your man had done to screw it up, or is it really a leak that coincidentally appeared after he did the work a couple of days ago?

There are no signs of leaks anywhere in the house btw, he thinks it's downstairs and wants to dig up the floors!

Any advice would be greatly welcome. Not the best time of year to be left without central heating!
If there never was a filling connection then how did the system ever get pressurised in the first place? There must be such a connection somewhere, and it may be a simple non-return valve from an attic tank. That valve could be stuck open or leaking slightly.

In your system there will be a cylinder (usually red). It has a bladder inside it and it is intended to apply air pressure to the system to prevent it from switching on and off repeatedly as the boiler heats the water and increases the pressure. That might need more air, and there is a Shraeder valve on it that allows you to pump it up with a car tyre foot pump.
If the cylinder is low on air pressure then even a very slight leak will cause the pressure in the system to drop rapidly. So will bleeding the rads.

It's difficult to diagnose anything over the Internet, but the usual rule of thumb is "who did what last?" I would take a close look at his "repressurising loop".
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08-12-2010, 21:31   #6
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Thanks a lot for your advice lads.

I entirely agree with you ART6, that's why I highly suspicious of what he has done! The only reason that I got him was that he was supposed to know the piping around the house but he seems to be clueless and I should have stuck with someone trustworthy, but anyway too late now.

I will take your adivce and check the pressure in EV.

Fingers, he said all he did was to connect a pipe (plastic) from mains system to the CH circuit. This connection is located in the attic, right next to the water tank and the (now old and disused) expansion tank (for, I suppose, when the system was an open system). It is not a NRV, I think, it's a simple one of those twisty things (red circular valve top... the type you normally see on pipes).

Thanks again, I appreciate your advice!
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08-12-2010, 22:53   #7
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Fingers, he said all he did was to connect a pipe (plastic) from mains system to the CH circuit. This connection is located in the attic, right next to the water tank and the (now old and disused) expansion tank (for, I suppose, when the system was an open system). It is not a NRV, I think, it's a simple one of those twisty things (red circular valve top... the type you normally see on pipes).

Thanks again, I appreciate your advice!
That being the case, how did you fill the system before, when it was a closed system?
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08-12-2010, 22:56   #8
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As ART6 pointed out, if the system didnt have a filling loop in the first place how was it pressurised? I have seen something like this before though as the filling loop was missing, the heating had a non-return vavle and you could hook up a filling loop to the heating from the mains and pressurise the system.

A non return valve doesnt have a Red circular turn off valve, thats a gate valve.Non return valve looks like this Link

It would seem you have a serious leak somewhere or with the way the weather is a pipe has burst somewhere.

If your in the Dublin area and need a number of a good plumber send me a pm and I'll pass it onto you....
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09-12-2010, 15:01   #9
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Thanks Mad M, that would be appreciated if you could pass on the number via PM.

Does the connection between mains and CH HAVE TO be via a NRV? Could the fact that it's not an NRV cause problems?
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09-12-2010, 16:20   #10
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Thanks Mad M, that would be appreciated if you could pass on the number via PM.

Does the connection between mains and CH HAVE TO be via a NRV? Could the fact that it's not an NRV cause problems?
The filling connection is more usually a braided metal flexible pipe that is connected to the system via a screw valve and a non-return valve. The braided pipe is usually open ended so that it can be connected when needed to a mains pipe and disconnected again when the system has been pressurised. The braided pipe is often near the boiler, particularly if the boiler is (say) a gas one that's indoors. The pipe might even be in the boiler casing in that case.

Having said that, I have seen systems where there was a permanent filling pipe from an attic tank via a non-return valve, although I have never understood what use that would be as there is not enough head pressure from such an arrangement to repressurise the system -- unless you happen to live in a four-storey building!
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09-12-2010, 16:57   #11
MuffinsDa
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The filling connection is more usually a braided metal flexible pipe that is connected to the system via a screw valve and a non-return valve. The braided pipe is usually open ended so that it can be connected when needed to a mains pipe and disconnected again when the system has been pressurised. The braided pipe is often near the boiler, particularly if the boiler is (say) a gas one that's indoors. The pipe might even be in the boiler casing in that case.

Having said that, I have seen systems where there was a permanent filling pipe from an attic tank via a non-return valve, although I have never understood what use that would be as there is not enough head pressure from such an arrangement to repressurise the system -- unless you happen to live in a four-storey building!
There are no braided metal flexible pipes in the boiler house...
The system used to be an open system and there is a disused expansion tank in the attic, the plumber has connected the repressurising thing there. I'll take a picture of it tonight and send it.
We do live in a very tall house alright, 2 stories above the ground floor, and this is on top of that so effectively in the 3rd floor!
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09-12-2010, 17:22   #12
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There are no braided metal flexible pipes in the boiler house...
The system used to be an open system and there is a disused expansion tank in the attic, the plumber has connected the repressurising thing there. I'll take a picture of it tonight and send it.
We do live in a very tall house alright, 2 stories above the ground floor, and this is on top of that so effectively in the 3rd floor!
Since ten metres of water head is approximately equivalent to one bar of pressure then a permanent connection to an attic tank might be enough to keep 0.5 bar of pressure in your system. In that case there would have to be a non return valve in the line from the tank, and non-return valves are never fail safe. If you don't have such a valve, but only a globe or gate valve (with a hand wheel) then that would be a good place to look for a leak back into the tank. Even so, the pressure shouldn't drop below the head of water pressure at the boiler. As a rule of thumb, if the tank is 5 metres above the boiler then the pressure in the system as shown on the gauge should be around 0.5 bar.

So, the test is to pressurise the system and leave the boiler off. Shut off the repressurising valve and see if the pressure drops over an hour or so below about 0.5 bar. If it does, you have a leak.

Clear as mud? Apologies!
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09-12-2010, 20:37   #13
MuffinsDa
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It is actually quite clear alright!

Boiler is off (has been off for 2 days now ), repressurized system, shut the gate valve. Pressure drops to 0 straight away (within 30 seconds or so!).

So... a giant leak somewhere downstairs? No sound of water, there are relatively small length of pipes downstairs, and wouldnt a leak that loses 1.5 bar in 10 seconds be quite noisy?

Or could it be a leak in the coil in tank?

I'm having a crowd called Leak Busters coming in tomorrow to look for leak...
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10-12-2010, 01:17   #14
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So... a giant leak somewhere downstairs? No sound of water, there are relatively small length of pipes downstairs, and wouldnt a leak that loses 1.5 bar in 10 seconds be quite noisy?

Or could it be a leak in the coil in tank?
Not necessarily. By the time it takes you to get the valve closed and to get around the system listening, the pressure is already gone, so you won't necessarily hear it, that plus depending on the type of hole, it mightn't necessarily make a hissing noise either??
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10-12-2010, 10:12   #15
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Thanks fingers.

We actually had the filling valve open and water running for a while, and listened for noises while it was running, and couldn't hear anything. Furthermore, we could here water definitely getting into the radiators.

As soon as the valve was closed then the pressure dropped to zero (within 30 seconds).
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