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