Central Heating Leak

[rwalters]

Hello all,

I have posted several messages on this forum about the pressure loss in our boiler. The loss is now getting far worse (1bar in 2 days), so it is now time to source the leak.

It is not on any of the radiators, they are all clean and dry. The boiler itself is clean, dry and no signs of leaks so I believe that the leak is in the pipework to the radiators.

I am also presuming that the leak is not from the upstairs rads, but correct me if I am wrong. The boiler has been loosing pressure for a year now, and now with it losing 1bar over 2 days I would have expected to see some signs on the ceilings downstairs, but they are all ok.

My question is, is there a gadget that a home user or plumber can use to detect water leaking from the system ?

I am obviously reluctant to start ripping up complete floors before I have exhausted all available options first.

Many Thanks

Richard

 

[ollski]

First check is always the automatic air vent on the boiler.

 

[rwalters]

I have checked that on previous occassions, it is clean, so is the overflow exiting the house.

 

[chrishutt]

System leaks are usually on radiator valves, especially the gland nuts under the plastic covers. Sometimes leaks occur within the boiler combustion chamber, so you need to have a gas competent person check that.

 

[rwalters]

I have removed all the plastic covers from the rads, they are all clean. I have also remoted the thermo valve top and they are clean too.

I have taken the side covers off the boiler and had a good look inside and it is very clean, so I do not believe it is the boiler.

How much water is 1bar ? We have a 4 bed house, with 12 radiators.

cheers

Richard

 

[chrishutt]

A 1 bar drop could represent hardly any water if your expansion vessel has failed! Sounds like you haven't actually checked inside the combustion chamber. Might be worth doing. Also you might be able to isolate the system pipework from the boiler and see which side the leak is.

 

[rwalters]

I have checked inside the combustion chamber this morning, some signs of green build up in their, but not much. It has dropped by 1 bar overnight, would I see water still in their or not ?

I didn't think about isolating the heating pipes, will do that now.

 

[ollski]

I didn't think about isolating the heating pipes, will do that now.

Nooooooooo, tell us what the boiler is first...most will leak like a sprinkler system if you turn them.

 

[rwalters]

I have repressurised the system to 1 bar and have isolated the CH feed and return pipes underneath the boiler. So my understanding now is that if the pressure drops now, the leak is inside the boiler. If the pressure stays stable, then the leak is in the heating pipework, am I correct?

Another little titbit, not sure if this will be connected or another issue that needs to be dealt with seperately. When we fill a bath and have the hot water on for a good period of time, the boiler temperature gauge goes off the scale, yesterday it went well past 100 and the pressure rises. When the bath has completed filling, if I open the hot water tap again, the boiler bangs and gurgles for a few seconds then the pressure and temperature start to drop. This doesn't happen if we are simply filling the sink with hot water, only when the hot water is on for a longer period, ie, filling a bath.

cheers guys, most helpful so far.

Regards

Richard

 

[ChrisR]

As previously advised, you do need to get the expansion vessel checked. You have BG cover so they should do it free if you explain about the pressure loss. 1 bar could represent a gallon or half a cup of water depending on the pressure vessel situation. A boiler engr would guess from the feel of refilling, which is having to go in.

You have "air" collecting on your rads. As said before, this is likely to be corrosion gas, which BG don't cover. If it gets to the boiler it escapes, dropping the pressure.

Many points around the system can leak only when hot and immediately evaporate the water so you never see it. Stains can be the only evidence.

 

[rwalters]

I didn't think about isolating the heating pipes, will do that now.

Nooooooooo, tell us what the boiler is first...most will leak like a sprinkler system if you turn them.

The boiler is a Vaillant VCW 242E.

 

[rwalters]

As previously advised, you do need to get the expansion vessel checked. You have BG cover so they should do it free if you explain about the pressure loss. 1 bar could represent a gallon or half a cup of water depending on the pressure vessel situation. A boiler engr would guess from the feel of refilling, which is having to go in.

You have "air" collecting on your rads. As said before, this is likely to be corrosion gas, which BG don't cover. If it gets to the boiler it escapes, dropping the pressure.

Many points around the system can leak only when hot and immediately evaporate the water so you never see it. Stains can be the only evidence.

Chris, thanks for the info. I agree on you with the "air" collecting, and i understand that air being vented off will result in the pressure dropping, but where is all the water going to that I use to keep topping the system back up.

The heating system has not been on for the last 4 months as it is hot weather, we don't need it, but it is still losing pressure. I have been watching the ceilings closely for the last year since we first noticed a slight drop in pressure, but now it has got worse, not signs at all of any stains on the ceilings downstairs.

 

[Agile]

I expect the expansion vessel is empty or faulty.

Also that the water is being forced out of the PRV vent ( its not an overflow! )

Tie a plastic bottle over the vent pipe and repressurise and see if water collects in the bottle.

If you have BG cover then I dont understand why you are bothering with this yourself.

Tony Glazier

 

[rwalters]

Tony,

I have put a finger from a rubber glove over the PRV last week and left it for 4 days, no water. I have spoken to BG about this on numerous times on the telephone and when an engineer has been onsite to look at other issues and they say they cannot do anything until there is evidence of a leak, ie staining on a ceiling, i think they dont want to start ripping up floors to find the problem.

 

[Agile]

Are you quite sure that the boiler PRV is connected to the vent pipe on the outside?

Sometimes we encounter ones which actually terminate within the wall!

One I went to on the fourth floor was delivering 6 litres per minute into the wall rubble cavity and appearing as dampness on the ground floor!

Tony Glazier