Boiler keeps losing CH pressure

[garycat]

We have just had our regular boiler replaced (i.e. a header tank in the loft) with a Vaillant system boiler that has a sealed CH system. We use the loop to pressurise it to ~2.0bar but in less than a day it drops to less than 0.5bar and shows a fault code.

There may have been a leak before, but because the header tank kept it topped up it was never noticed. Now it is a sealed system at higher pressure it means our heating shuts down every day.

The plumber says we probably have a leak in the system and will have to dig up the pipes to find it - they are buried in concrete, or reroute the pipes via the loft which will cost about £3K.

Is there any other possible solution before

[Ricky_M]

2 bar is too high, should be set between 1 - 1.5 bar when cold.

Could be a number of things. Because you're setting it to high, could be expanding to 3 bar and activating the PRV and dumping the pressure, have you noticed and water around the PRV discharge pipe? Although unlikely as it wouldn't ussually expand by a bar.

How long has the boiler been fitted and is it a large system? Most boilers have an automatic air vent and will lose pressure as it vents off the excess air in the system, also chemical inhibitor will produce quite a bit of gas (hydrogen I think?), so if it has only been a week or so, give it a chance to settle.

Pipes buried in screed doesn't sound promising though, may have to cap off the downstairs circuit and feed the rads from the upstair circuit. Good luck!

[Trevelyan]

My parents had a similar problem in their house - pipes buried in the concrete floor which started to leak. They still had the type of CH system fed by a header tank so that wasn't the issue, but the constant leak within the concrete started causing damp problems, particularly as they had wooden floors laid on top. In the end I bit the bullet last winter and replaced all of the downstairs pipework, running it all behind the skirting boards and abandoning the old stuff.

You could try something like this to see if it helps:

http://www.screwfix.com/prods/45902/Plumbing/Centr...

I've never used the stuff before, but presumably it's similar to RadWeld for cars. To be honest I have my doubts that it'll help much in your case as it's meant for small leaks, whereas I guess your leaks are a bit more serious.

[john_p]

I had this, pipes in concrete leaking. Mine lost pressure a lot slower than in this case, but you could still find the leak because the floor, wall and skirting got noticably moist. Might be worth a look around likely pipe routes and lifting the odd bit of carpet to check?

Might be worth tying a sandwich bag over the boiler overflow / PRV pipe (on the outside wall) just to see if it's leaking water via that route, but I bet you'd notice that much water.

[b2dan]

I had this problem recently, it kept losing pressure from 1.0bar to 0.2bar when cold.

Turns out my expansion vessel was flat. Charged this up using a bicycle pump and hey presto it's working fine again! It now happily sits at 1.0bar and moves upto two when warm. It used to be hovering around the 3.5bar mark when warm.

Dan

[CO2000]

If you do need to hunt for the leak a Thermal Camera may well pick up the place where it is leaking.

You could prob hire them for not too much money depending on your location.

[Beardy10]

We have a Vaillant system which has been doing just this for three years...they key is as others have said not to top the system up too high. Something like 1.O bar when cold is fine. It's got my plumber (not the one that installed it completely baffled. We do have some pipes laid in concrete on the ground floor but after three years you would think there would be a sign of a leak ?

Our system has needed to be topped up probably every two weeks since we've had it which is not good for the system but we are probably going to sell the house this year so I am not going to spend fortunes investigating it.

[garycat]

Thanks for all the advice guys. I think I'll try the leak sealer and reduce the pressure a bit.

Surely plumbers have some pressure testing device that they can use to check each section of pipe between each radiator to isolate the leak?

Edited by garycat on Sunday 7th February 22:56

[Torquey]

I've used this kind of stuff.
http://www.plumbnation.co.uk/site/fernox-f4-expres...

Went from 1.5bar to 0 in around 3-4 days. This has completely sealed it and it hasnt budged in 4 weeks. Definately worth a try in your situation.

[Ferg]

garycat said:

Surely plumbers have some pressure testing device that they can use to check each section of pipe between each radiator to isolate the leak?

Difficult given the way heating systems are piped.

[garycat]

Well the leak sealer didn't work so I guess I'll have to try some other options.

We traced round the floor where the existing heating pipes go and couldn't find any evidence of a leak, but under the carpet are vinyl tiles on top of bitumen so the damp may not be getting through.

Is the PRV pipe a copper pipe that goes through the outside wall and then is curved round in a U shape so it points back towards the brickwork?

Is pumping up the expansion vessel a DIY job?

Otherwise what would be the approx cost of replacing all the pipework on a 3 bed bungalow. All the flooring is going to be replaced anyway so digging up the concrete isnt a problem.

[Beardy10]

That is the PRV pipe...that's where mine loses pressure from.

[john_p]

I did read a tip somewhere while diagnosing the same problem that the PRV can leak very gently and you won't notice it. Hence you tie a freezer bag or similar around so you can see how much water is coming out over a longer period.

[R60EST]

I've had a leaking PRV in the past . At the rate yours is losing pressure you should see a constant drip coming from the end of the pipe outside . It is a relatively cheap fix if that is what it turns out to be.

[Ricky_M]

john_p said:

I did read a tip somewhere while diagnosing the same problem that the PRV can leak very gently and you won't notice it. Hence you tie a freezer bag or similar around so you can see how much water is coming out over a longer period.

Be careful doing that in this weather, it can freeze up and block the PRV, had it happen to a customer who had a knackered expansion vessel. He put a watering can under his PRV outlet, it froze up and the boiler released over 3 bar of pressure through all the joints inside the boiler!

Expansion vessels are easy to re-charge, they have a tyre valve on the top whcih you simply pump up.

Easiest way to do it is pressurise the boiler to 0.5 bar and pump the vessel until the pressure rises to 1.5 bar.

But if the diaphragm in the vessel has ruptured, it will have to be replaced. Can be a pig of a job on certain boilers! Not a Baxi 105e by any chance is it?

[B17NNS]

Ricky_M said:

Not a Baxi 105e by any chance is it?

I've got one of them

Similar problem and now I also have one of these.

[Ricky_M]

Was going to say if you have a 105e, get an external expansion vessel installed if you have the space. Most of the time they have to come off the wall to replace the vessel. Nightmare of a job!