I think I've got a leak after new CH installed

Sheff · 5 May 2006

I've checked the threads and done a search and I don't *think* this has been covered before, but aplogies if it has.

I've just had an old open CH system with hot water tank replaced by a closed combi boiler system (Vaillant ecotec 831). The system was powerflushed as part of the installation.

Following the install the system is rapidly depressurising from 1.2bar down to 0.2 bar in about 90 minutes. My plumber's been back to check all of the pipework that they did during the install and there are no leaks there so he's suggested that there's a leak somewhere else in the system. All of the radiators seem intact so I guess it's a leak in the pipeework somewhere, but where?

There's no water dripping through the ceiling so I figure the leak must be downstairs in the pipework. Unfortunately it's a newish house (about 30 years old) and the floors are solid concrete as far as I can tell.

Do you think that this is a leak, and if so, how the hell can I find where it is for my plumber to sort out? His suggestion was to run the system with the water inlet valves open enough to let water in at the same rate it's leaking out, and then look for the wet patch!

Thanks in advance for any help.

croydoncorgi · 5 May 2006

Leakage at that rate might be audible. Your plumber should know how to listen for leaks.

Leaving the system fill open to keep the pressure up is extremely risky and medium term will trash your new boiler. Adding water quickly replaces any inhibitor that might be in the system. Adding fresh, aerated water out of the mains continuously will rapidly set up corrosion of the system, especially inside the rads, leading to brown sludge everywhere, especially in the secondary heat exchanger of the boiler! All Bad!

If the system was leaking continually while it was still open-vent, I suppose you might not have noticed - but it sounds like a big leak! You need to find it / them.

Possibly better to run the system hot and look for a HOT patch rather than a wet one....IR termometers are relatively cheap and might work. IR thermal imaging is better.

joe-90 · 5 May 2006

Concrete is well-known for corroding copper over that sort of period.

As the combi is a closed system, you need very little leakage for the pressure to be lost (think of a uncorking the pressure of a bottle of fizzy drink).

Another possibility is that the hot pipes dry the leaking water before it drips so look for staining.

joe

jiminblack · 5 May 2006

I'm not sure of the construction of the Heat exchanger on these models but, it could be that it's leaking internally within the heat exchanger. You won't see any water because it's going down the condense drain. You can easily check it out by turning off the CH flow and return valves on the boiler. Pressure still going down...leak on boiler!!

Sheff · 5 May 2006

Excellent help guys. I'm very grateful.

I'll try to check out the possibility of a leak in the heat exchanger, and I'll have a listen to the pipework the next time we fill the system up.

Judging by the amount of water that's needed to fill the system after it's depressurised I reckon that it's losing a few litres of water every time. It's certainly not losing all of the 100+ litres in the system. I think (hope) I'd have noticed that!! When it was an open system the radiators didn't need bleeding too frequently, so I suspect this is a leak that's come about either from the powerflush, or has popped now the system's been pressurised a little.

I'd thought of getting hold of a moisture meter and looking for any areas of the foundation/outside brickwork that seemed damper than the rest of the house, but I like the thought of looking for a hot leak much more.

Where could I get a thermal imaging camera from? Could I hire one from HSS, or is it a question of getting a specialist in to survey for me (sounds expensive)?

Please keep the ideas coming!!!

Agile · 5 May 2006

Do the boiler test first, with boiler off!

If thats OK then do what your fellow suggests and set or leave with a higher presssure of bit over 2 Bar as that will increase the leak rate and increase the chance of seeing it. Again do it COLD!

After a couple of hours feel every rad valve for a wet finger, look at the brickwork outside and particularly look at the concrete where the tube goes down into it from a rad.

90% of leaks I have found in concrete have been on the elbow to turn horizontal from that vertical.

Tony

Sheff · 5 May 2006

I'll try that thanks Tony. Is it likely to be the heat exchanger on a brand new boiler?

I'm struggling to see how 10-15 litres of water could soak away from a pipe in concrete, but I can't think of many other alternatives.

I think I might have found a small leak coming out of the floor by one of the downstairs rads though...

croydoncorgi · 5 May 2006

At the rate of loss you suggest, a heat exchanger problem (unlikely but possible on a new boiler) would be immediately evident by water running into the condensate drain with the burner off and boiler cold.

But the suggestion above (isolate the boiler and see if the pressure still drops) should confirm this very quickly.

doitall · 5 May 2006

Sheff said:
I'll try that thanks Tony. Is it likely to be the heat exchanger on a brand new boiler?

I'm struggling to see how 10-15 litres of water could soak away from a pipe in concrete, but I can't think of many other alternatives.

I think I might have found a small leak coming out of the floor by one of the downstairs rads though...

Your not loosing 10-15 litres of water, more in the 1-2 litre range.

Have you checked the pressure relieve valve outside by tieing a plastic bag over the end

Sheff · 6 May 2006

doitall said:
Your not loosing 10-15 litres of water, more in the 1-2 litre range.

Have you checked the pressure relieve valve outside by tieing a plastic bag over the end

I figured I was losing 2-3 litres each time, but I've filled it up 5 times now, so wherever this leak is it's absorbed, or soaked-away, 5-15 litres in total without showing any visible evidence other than a really small damp patch under the carpet by one rad.

I don't think it's the PRV, but it's easy to test so I'll check that out too thanks.

joe-90 · 6 May 2006

You simply cannot lose that amount of water above ground and not notice it. It would leak through you ceiling or ruin your carpets.

The only likely explanation I can think of is this:

You have a leak under the concrete floor. The pipe is laid under the concrete and has corroded away. The water that is leaking is (and possibly has been for years) leaking away into the hardcore under your concrete. It is then soaking away into the earth beneath your house.
To put it in a nutshell, you have a soakaway under your house.

If this is the case you need to remedy it urgently as the foundations may well begin to sink.

Maybe worth contacting your insurance company?

joe

doitall · 6 May 2006

Sheff said:
5-15 litres in total without showing any visible evidence other than a really small damp patch under the carpet by one rad.

I don't think it's the PRV, but it's easy to test so I'll check that out too thanks.

You have a small leak which will dry every time the heating comes on.

Where the damp patch is, turn the heating off and allow to cool, check for leaks around the valve, by running your fingers around the pipe any small leak will show.

Check the pipe for signs of brown staining, use a mirror to see around the back, check all the others as well.

Soggy_weetabix · 6 May 2006

You could try fernox internal leak sealant. Big ask of it though - but one worth trying even if you have to 'double dose' the system.

David

Sheff · 12 May 2006

Hi guys, a quick update for everyone who's helped:

The plumber's retruned today and has dug the floor up where I'd identified the leak. It turns out there was a 4cm hairline crack in the pipe going from the boiler to the radiator. The offending bit of copper's been removed and replaced and the system is now (so far - touch wood) holding pressure (up to 1.8bar when there's a CH demand). There was no obvious sign of any significant damage to the foundations, presumably as the system had previously been open and the pipe wasn't leaking at ambient pressure.

Anyway, can I just say thank you for all the help that was freely offered. I'm very grateful

croydoncorgi · 12 May 2006

Hmmmm....
Crack running ALONG the pipe... wonder what caused that? Very odd.

diynot

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I think I've got a leak after new CH installed

Soggy_weetabix

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