Leaking combi boiler system

[RogBroadie]

Hi,

Our combi boiler system has been leaking pressure these last couple of months. It is leaking faster and faster. It now needs re-pressurising almost every day.

We have had the boiler serviced and they claim there is nothing wrong with the expansion vessel. The pressure relief valve has been changed.

They all say that there is a leak, but despite keeping the pressure high and checking every bit of pipe we can see, no leaks are evident. We don't have any pipes below ground floor level, so anything that is leaking must be producing a pool of water somewhere - but no damp ceilings are evident from those pipes under the first floor floorboards.

Can the boiler engineers be wrong? Is this something to do with the expansion vessel even though they say it is OK?

And how much water is involved and leaking, given that we have 9 radiators in a 3-storey house. Is this just a tiny leak that is evaporating or several pints of water a day that must be going somewhere. Certainly feels like several pints when I have to let more water in to re-pressurise the system.

All help appreciated - we are going spare with this.

Roger.

 

[muggles]

Tape a sandwich bag over the pressure relief outlet and see if it collects water, if it does then that's where the water is going. Also watch your pressure as the boiler heats up, does it change much from cold to hot?

 

[RogBroadie]

Thanks, will give that a try. What should I be looking for in pressure change as it heats up, lots or little? I think it rises about a quarter of a bar when the central heating starts pumping.

 

[MANDATE]

My understanding is that the pressure should rise about 1bar.
Why would you want to keep the pressure high? when the PRV opens at 3bar.

Could be the PRV is not fully sealed and a small loss of water will become a bigger loss when heating is on.
What pressure is it set to with heating off?

 

[MonkeyBoyMorton]

Have you checked if water is dripping from the condensation outlet pipe?

This is a white approx 1" plastic pipe which is usaully routes outside to a grid. Stick a cup or jug under it and see if it fills up.

 

[bengasman]

Have you checked if water is dripping from the condensation outlet pipe?

This is a white approx 1" plastic pipe which is usaully routes outside to a grid. Stick a cup or jug under it and see if it fills up.

If no water at all comes out, it indicates the boiler doesn't work, not that it leaks or doesn't leak.

Dropping pressure = leak, end of.

 

[Agile]

Oh dear!

You have not said any details of your boiler or the pressures involved.

Top to 1.5 Bar cold and it should rise by about 0.3-0.4 Bar when hot.

Its quite possible there is a leak inside the boiler and the water is being evaporated.

From 1.5 Bar to 0.5 Bar, both cold, there is about 3 litres of water IF everything is correctly set.

Did the service include opening the boiler and the combustion chamber?

Without all those details we cannot give you informed advice!

Tony