How do I find a (small) leak from pressurised system

[JImCPN]

I see that there was a post in November that refers to a LARGE leak, but ours is much smaller (needs topping up every ten days to two weeks, perhaps a litre over that period). It has been going on for about six months. The boiler is new since last year; however, to cover all bases, we called the installer out and, predictably, they found no fault. Interestingly, they had no suggestions as to what to do next. Most of the pipework is exposed and there is no sign of leakage anywhere. There is a small amount of piping boxed in and I (rather cleverly I thought, my wife will be SO impressed when I find the leak) invested in a cheap borescope and had a look. As far as I can tell, it is all dry - but I can't see everything and the quality is not brilliant.

It is certainly irritating .... and my wife has nightmares of the house foundations gradually dissolving. My questions are

1) How common is this sort of slow leakage and is it likely to get worse, assuming there is a small leak somewhere?
2) Are there other methods of leak detection? The previous post mentioned a specialist firm, but that sounds pricy - is it? What methods do they use? I just have a feeling that a really expensive borescope used by an expert may do the job ... but where do I get advice from without committing myself to a large invoice?
3) How common is this problem?

Jim

 

[Chuck]

Always start with the low tech basics. First, because it's easy, go round and have a good look, with a magnifying glass and good lighting at every joint and valve stem, etc. for signs of leaking. Next step is to isolate the boiler from the radiator system, there may be isolating valves already installed for just this purpose. See whether the pressure drop is in the boiler or radiators half of the system. If it's in the radiators. One can then proceed to 'divide and conquer' by testing the upper floor and lower floors separately, etc.

If it's a newish system that originally worked fine I'd have 'Automatic air vent' near the top of my list of suspects. This will/should be at the highest point on the system. Some installers fit an isolation valve in series with them so that after the first few months, when their work is largely done because once the dissolved air is out and new pipework has finished forming its 'passivating layer', they can be isolated to prevent leaking.

You can also try closing the TRVs and lockshields on groups of radiators to see if/when the leak stops. But in my experience most leaks from radiators/valves are visible.

There are various hi-tech methods, e.g. using tracer gas, putting fluorescent dye into the system and searching with UV, thermal cameras to detect damp patches, ultrasound detectors to listen for the sound of a leak, etc. A leak finding company who uses these techniques will be moderately expensive, i.e. a few hundred quid, but some may offer a domestic customer a fixed fee or no win no fee deal.

Another approach is to wait a while and top up every week, keeping a record of how much the pressure has dropped. It will gradually get worse and hence easier to find.

 

[JImCPN]

Always start with the low tech basics. First, because it's easy, go round and have a good look, with a magnifying glass and good lighting at every joint and valve stem, etc. for signs of leaking. Next step is to isolate the boiler from the radiator system, there may be isolating valves already installed for just this purpose. See whether the pressure drop is in the boiler or radiators half of the system. If its in the radiators. One can then proceed to 'divide and conquer' by testing the upper floor and lower floors separately, etc.

If it's a newish system that originally worked fine I'd have 'Automatic air vent' near the top of my list of suspects. This will/should be at the highest point on the system. Some installers fit an isolation valve in series with them so that after the first few months, when their work is largely done because the new pipework has finished forming its 'passivating layer', they can be isolated to prevent leaking.

You can also try closing the TRVs and lockshields on groups of radiators to see if/when the leak stops. But in my experience most leaks from radiators/valves are visible.

There are various hi-tech methods, e.g. using tracer gas, putting fluorescent dye into the system and searching with UV, thermal cameras to detect damp patches, ultrasound detectors to listen for the sound of a leak, etc. A leak finding company who uses these techniques will be moderately expensive, i.e. a few hundred quid, but some may offer a domestic customer a fixed fee or no win no fee deal.

Another approach is to wait a while and top up every week, keeping a record of how much the pressure has dropped. It will gradually get worse and hence easier to find.

That is so helpful, thank you! Actually, re first paragraph, I forgot to mention that as part of the fault finding process the firm that installed the new boiler did do that .. ie they came and isolated the boiler (the radiators are old and have no isolating valves) and we watched the pressure drop as usual on the radiator side. We have tried tissue paper on all the valves ... they remain dry.
I suspect that my toleration with using the technique in your last paragraph will be rather more than my wife's .. who will favour the suggestion of the paragraph before.

 

[Chuck]

I suspect that my toleration with using the technique in your last paragraph will be rather more than my wife's .. who will favour the suggestion of the paragraph before.

You'd better start calling 'leak finding services' then.

 

[WC1]

Have you been all over the rads with kitchen towel?

 

[gmartine]

If you can add your wife or your nastiest peppy le pew scent to the system and follow your nose.

(Didn't you recommend that once WC1?)

 

[WC1]

Still waiting for a chance to try.
C'mon Jim, get some old spice down it.

 

[JImCPN]

You'd better start calling 'leak finding services' then.

Still waiting for a chance to try.
C'mon Jim, get some old spice down it.

Still waiting for a chance to try.
C'mon Jim, get some old spice down it.

Just logged in again to see this - is it a serious suggestion?! Its just that I succumbed to pressure and called a very helpful leak detection service who gave advice as follows

1) A top-up every two weeks is unlikely to be found, it is just too small. We don't want you to waste your money on the call-out and not find anything when we do.
2) At this level of leakage it is not going to cause damage (but I did read somewhere on other firms websites that it may re corrosion etc. Is this true?)
3) It is likely to get worse, especially as the winter approaches and we use the CH more.
4) Call us again if / when it does

She sounded knowledgeable and the company answered the phone within two rings. I'd love to get confirmatory thoughts that this advice is correct and then I can go back to my wife with a definitive answer ... with a view to using this firm in the future.

 

[John.g]

If not a combi boiler you will have a HW cylinder with a coil in it.

 

[CHRISX]

That is so helpful, thank you! Actually, re first paragraph, I forgot to mention that as part of the fault finding process the firm that installed the new boiler did do that .. ie they came and isolated the boiler (the radiators are old and have no isolating valves) and we watched the pressure drop as usual on the radiator side. We have tried tissue paper on all the valves *** they remain dry.
I suspect that my toleration with using the technique in your last paragraph will be rather more than my wife's .. who will favour the suggestion of the paragraph before.

Hello JImCPN,

I take it that You have a Heat only Boiler - not a Combi / Heating & Hot Water Boiler ?

The reason I ask is just to check what happened when your Boiler installers isolated the Boiler from the Heating system Radiators and Pipework and still saw a pressure drop:

If the Boiler is a Combi usually the only pressure gauge on the system is on the Boiler and if the Heating Flow and Return isolating valves on the Boiler are turned off the pressure gauge would not be able to show a pressure drop from the Heating system / Radiators and Pipework.

If it is a Combi Boiler and the pressure gauge showed a drop when the installers isolated it from the Heating system by turning off the valves on the Boiler Flow and Return pipework I would be looking at the Boiler Pressure Relief valve discharge pipe end to see if there was dripping.

You should check this especially when the Heating is on as the system pressure increases as the water expands but also when it is off - any dripping from the discharge pipe would mean that the PRV was not remaining fully closed / holding pressure.

However although a dripping PRV valve could easily cause the amount of pressure loss that you described over a 2 week period I cannot imagine that it could cause a visible pressure drop on the gauge just while the Boiler isolating valves were turned off and the gauge was being observed because if that was the case the system pressure would be dropping much quicker that needing to be topped up every 2 weeks.

If you have a Heat only Boiler on a sealed system has anyone looked at the end of the discharge pipe from the Pressure Relief Valve to check for water dripping?

There should be on a discharge pipe from the PRV that goes to outside the building - like a metal overflow pipe - check to see if that has any drips coming from it - you should check this especially when the Heating is on as the system pressure increases - but also when it is off.

Chris

 

[John.g]

Tape a small plastic bag to the end of the PRV waste pipe, that will catch even minute drops if leaking.

 

[JImCPN]

Tape a small plastic bag to the end of the PRV waste pipe, that will catch even minute drops if leaking.

Hello JImCPN,

I take it that You have a Heat only Boiler - not a Combi / Heating & Hot Water Boiler ?

The reason I ask is just to check what happened when your Boiler installers isolated the Boiler from the Heating system Radiators and Pipework and still saw a pressure drop:

If the Boiler is a Combi usually the only pressure gauge on the system is on the Boiler and if the Heating Flow and Return isolating valves on the Boiler are turned off the pressure gauge would not be able to show a pressure drop from the Heating system / Radiators and Pipework.

If it is a Combi Boiler and the pressure gauge showed a drop when the installers isolated it from the Heating system by turning off the valves on the Boiler Flow and Return pipework I would be looking at the Boiler Pressure Relief valve discharge pipe end to see if there was dripping.

You should check this especially when the Heating is on as the system pressure increases as the water expands but also when it is off - any dripping from the discharge pipe would mean that the PRV was not remaining fully closed / holding pressure.

However although a dripping PRV valve could easily cause the amount of pressure loss that you described over a 2 week period I cannot imagine that it could cause a visible pressure drop on the gauge just while the Boiler isolating valves were turned off and the gauge was being observed because if that was the case the system pressure would be dropping much quicker that needing to be topped up every 2 weeks.

If you have a Heat only Boiler on a sealed system has anyone looked at the end of the discharge pipe from the Pressure Relief Valve to check for water dripping?

There should be on a discharge pipe from the PRV that goes to outside the building - like a metal overflow pipe - check to see if that has any drips coming from it - you should check this especially when the Heating is on as the system pressure increases - but also when it is off.

Chris

Thanks Chris. It is a CombiBoiler with one gauge ... but as part of their proving that the boiler was not at fault they isolated the boiler and put another (temporary) pressure gauge on the radiator side. As predicted, the boiler pressure remained fine while we watched the other gauge slowly dropping as before. Definitely a leak somewhere that doesn't involve the boiler

 

[CHRISX]

Thanks Chris. It is a CombiBoiler with one gauge *** but as part of their proving that the boiler was not at fault they isolated the boiler and put another (temporary) pressure gauge on the radiator side. As predicted, the boiler pressure remained fine while we watched the other gauge slowly dropping as before. Definitely a leak somewhere that doesn't involve the boiler

Hello again JImCPN,

Thanks for letting us know that information - it rules out what I was describing regarding a PRV dripping.

When you describe seeing the other pressure gauge dropping do you mean that you were watching it over a period of time / during a few days or that the gauge was dropping while the Boiler installers were there ?

Good Luck in finding the cause of the system pressure loss.

Chris

 

[John.g]

Thanks Chris. It is a CombiBoiler with one gauge *** but as part of their proving that the boiler was not at fault they isolated the boiler and put another (temporary) pressure gauge on the radiator side. As predicted, the boiler pressure remained fine while we watched the other gauge slowly dropping as before. Definitely a leak somewhere that doesn't involve the boiler

The pressure should fall faster with the boiler isolated as there is no expansion vessel on the CH system then and should fall almost "instantly" to ~ 0.4/0.5 bar; the static head from the upstairs rads and then fall at a much slower pace, except that your CH system still contains entrained air, unlikely after all this time?.

 

[CHRISX]

The pressure should fall faster with the boiler isolated as there is no expansion vessel on the CH system then and should fall almost "instantly" to ~ 0.4/0.5 bar; the static head from the upstairs rads and then fall at a much slower pace, except that your CH system still contains entrained air, unlikely after all this time?.

Hello John.g,

I cannot agree with what you stated about the pressure drop falling faster because the Combi Boiler Expansion vessel was isolated from the Heating system - however I am open to further explanation if you feel happy to write it ?

Here are my views:

When the Combi Boiler Flow and Return isolating valves were turned off obviously the Boiler would be off and whatever pressure was in the Heating system radiators and pipework at that time would not drop any faster because there was no connection to an Expansion vessel.

If there was 1 Bar pressure in the system with the Combi isolating valves open and therefore the Boiler Expansion vessel membrane had that pressure applied to it that would not affect the speed of a pressure drop which was being caused by a water leak or an air leak within the Heating system.

However if the Heating has been on and the system pressure has risen to perhaps 2 bar with that pressure rise having been taken up by the Expansion vessel membrane deflecting inside the vessel that rise in pressure / deflection of the Expansion vessel membrane would cause a pressure drop to fall faster for a short period of time until the system pressure fell to the cold temperature pressure when the drop would be slower.

Whatever water pressure was in the system with or without the Combi Boiler / Expansion vessel being isolated will affect how quickly the pressure drop falls - the higher the pressure the faster the pressure drop.

As I mentioned above I would welcome your reply - especially if I find that I am wrong in what I have stated ?

Chris

 

[gmartine]

Yes, introducing

Just logged in again to see this - is it a serious suggestion?! Its just that I succumbed to pressure and called a very helpful leak detection service who gave advice as follows

1) A top-up every two weeks is unlikely to be found, it is just too small. We don't want you to waste your money on the call-out and not find anything when we do.
2) At this level of leakage it is not going to cause damage (but I did read somewhere on other firms websites that it may re corrosion etc. Is this true?)
3) It is likely to get worse, especially as the winter approaches and we use the CH more.
4) Call us again if / when it does

She sounded knowledgeable and the company answered the phone within two rings. I'd love to get confirmatory thoughts that this advice is correct and then I can go back to my wife with a definitive answer *** with a view to using this firm in the future.

Yes, it's a very serious suggestion. What have you got to lose except a couple of quid on some scent.

The only issue is you're probably not running your central heating atm which means it won't circulate around the system as freely but certainly consider doing it when you do switch your heating on if the problem still persists.

 

[John.g]

Hello John.g,

I cannot agree with what you stated about the pressure drop falling faster because the Combi Boiler Expansion vessel was isolated from the Heating system - however I am open to further explanation if you feel happy to write it ?

Here are my views:

When the Combi Boiler Flow and Return isolating valves were turned off obviously the Boiler would be off and whatever pressure was in the Heating system radiators and pipework at that time would not drop any faster because there was no connection to an Expansion vessel.

If there was 1 Bar pressure in the system with the Combi isolating valves open and therefore the Boiler Expansion vessel membrane had that pressure applied to it that would not affect the speed of a pressure drop which was being caused by a water leak or an air leak within the Heating system.

However if the Heating has been on and the system pressure has risen to perhaps 2 bar with that pressure rise having been taken up by the Expansion vessel membrane deflecting inside the vessel that rise in pressure / deflection of the Expansion vessel membrane would cause a pressure drop to fall faster for a short period of time until the system pressure fell to the cold temperature pressure when the drop would be slower.

Whatever water pressure was in the system with or without the Combi Boiler / Expansion vessel being isolated will affect how quickly the pressure drop falls - the higher the pressure the faster the pressure drop.

As I mentioned above I would welcome your reply - especially if I find that I am wrong in what I have stated ?

Chris

First of all re the main thread, I would consider 1litre/2 weeks or 50 litres/year a fairly bad leak, I keep a eye on a neighbour's (oil fired) sealed system and only top it up every 18/24 months from 1 bar to 1.5 bar (cold) it has a 10 litre EV with a pre charge pressure of 1 bar so in falling from 1.5 bar (cold) to 1.0 bar it will still only have used its reserve of 2 litres in this time.

Re pressure testing, assuming a cold pressure of 2.5 bar in both cases and assuming a 10 litre EV with a pre charge pressure of 1 bar then with the EV connected to the system it will contain ( the reserve) 4.3 litres of water at 2.5 bar so the system must leak/lose 4.3 litres before the pressure falls to 1 bar.
With no EV connected to the system, theoretically at least, if system has no entrained air then it should take practically nil litres to pressurize to 2.5 bar (once system is full) since water is incompressible so the pressure should fall very rapidly to 1 bar and also to ~ 0.4bar, the static head of the system, thereafter should fall at a very slow rate due to the system contents and lower pressure.

 

[SimonG]

Over pressurise the system then double check radiator valves, joints etc.

 

[John.g]

Also give all the lock shield valve gland nuts a nip up.

 

[grahamgorb65]

have you tried adding leak sealer to the system.

 

[CHRISX]

First of all re the main thread, I would consider 1litre/2 weeks or 50 litres/year a fairly bad leak, I keep a eye on a neighbour's (oil fired) sealed system and only top it up every 18/24 months from 1 bar to 1.5 bar (cold) it has a 10 litre EV with a pre charge pressure of 1 bar so in falling from 1.5 bar (cold) to 1.0 bar it will still only have used its reserve of 2 litres in this time.

Re pressure testing, assuming a cold pressure of 2.5 bar in both cases and assuming a 10 litre EV with a pre charge pressure of 1 bar then with the EV connected to the system it will contain ( the reserve) 4.3 litres of water at 2.5 bar so the system must leak/lose 4.3 litres before the pressure falls to 1 bar.
With no EV connected to the system, theoretically at least, if system has no entrained air then it should take practically nil litres to pressurize to 2.5 bar (once system is full) since water is incompressible so the pressure should fall very rapidly to 1 bar and also to ~ 0.4bar, the static head of the system, thereafter should fall at a very slow rate due to the system contents and lower pressure.

Hello John.g,

Thanks for replying with the explanation.

I had not taken into consideration the additional capacity that the Expansion vessel reserve volume has - however that expansion capacity is only pertinent if it is being used when the system water has expanded due to being heated.

Without wanting to seem pedantic just some further thoughts:

As a sealed Heating system PRV would be set at 3 Bar the system cold pressure should be closer to 1 - 1.5 Bar theoretically rising to about 2.5 Bar when the Heating system has heated up / system water had expanded so the Expansion vessel would have to accept a lower amount of expansion / reserve capacity than you calculated.

Something else that I would have been thinking when I wrote my previous reply to you was that if a sealed Heating system has a capacity of 100 litres when filled and has been fully vented to remove any air from the system it has only 100 litres.

There is not for example 104 litres of water even when the water is heated - although the water would have expanded by for example 4 litres when heated [not calculated] the system capacity would still have been 100 litres.

In my previous reply when I was trying to explain why I could not agree with what you had written I had it in mind that the Heating system capacity is static in terms of actual water content whether the Expansion vessel was isolated from the system or not - and as we would be checking the system pressure drop from cold - not when the system was being heated [EV isolated so Boiler off] there would be no difference in the system water volume and at a cold water pressure of approximately 1 Bar I could not see any difference in the rate that the pressure would drop with or without the Expansion vessel isolated from the system.

Chris

 

[John.g]

Hi Chris,

Not quite sure from the above but are you (still) of the opinion that there is no difference in the rate of pressure loss in a system under (cold) test whether connected to a EV or not?.

 

[CHRISX]

Hi Chris,

Not quite sure from the above but are you (still) of the opinion that there is no difference in the rate of pressure loss in a system under (cold) test whether connected to a EV or not?.

Hello again John.g,

From a combination of reading your explanation and what I was thinking when I wrote my first and second replies to you I have realised that when the initial pressurisation of a sealed Heating system is done - for example to the recommended cold temperature pressure of 1 Bar - that pressurisation is deflecting the Expansion vessel membrane so that deflection will be slowly returning back to or towards its pre-pressurisation form as part of the pressure drop when there is a leak from the sealed system.

I agree that would take more time to cause a pressure drop than a sealed system which had the same initial cold temperature pressure of 1 Bar and was on a pressure drop test with the Expansion vessel isolated from the system.

I have been a Heating Engineer, Plumber and Gas Engineer for well over 50 years and this is the first time that this subject has ever come up to me regarding whether a sealed Heating system pressure drop would be faster with or without an Expansion vessel isolated from the system.

I have often isolated the Expansion vessel on a sealed Heating system or isolated the Combination Boiler to prove that there was a leak somewhere on the pipework, radiators or radiator valves etc. but it has never occurred to me to be thinking along the lines of the speed of a pressure drop being different with the Combination Boiler or Heat only Boiler sealed system Expansion vessel isolated from the radiators and pipework.

Having written that - any sealed Heating system pressure loss investigation that I have ever done has involved just finding the cause so the particular test that we have corresponded about here regarding the speed difference of the pressure drop with or without the Expansion vessel isolated from the system was something that would not have been on my mind.

Thanks again for writing your explanation in reply to my initial comments.

Chris

 

[John.g]

Yes, all very interesting.

I suppose that when a system gas boiler is isolated and being tested that the EV is still "attached" so even more attention required to ensure no pressure loss if the test is very short term.

Generally, EV pre charge pressure is normally 0.75 to 1 bar even though theoretically 0.5 bar is enough for a system static head.
Also, knowing the actual pre charge and filling pressures is very useful as one can get a very accurate feel for the vol of water leaked, for example, a 10 litre EV with pre charge/filling pressures of 1.0/1.5 bar will have a reserve of 2 litres so if/when the final pressure eventually drops to 1.0 bar then 2 litres has been lost.
For interest, I attach a snapshot of the calcs I have used for decades, is is based on the fact that (air side) vol is inversely proportional to absolute pressure. So a pre charge/fill pressure of 1.0/1.5 bar gives a (10*2/2.5), 8 litre air side vol and (10-8), 2 litre water side (reserve) vol and so on.

 

[Ian118]

Do the radiator pipes downstairs come up out of a concrete floor ?