can air in a sealed heating system cause pressure loss?

[DiyAngel]

As a certain large gas company cant explain why we are losing pressure in our sealed heating system. They have decided we have a leak. Problem is there is no evidence of a leak anywhere even downstairs where we have wooden floors.

PRV has a balloon on it so we know thats not the problem. We have also ballooned the overflows and although one has inflated slightly with air there is no water in the balloon. The expansion vessel was faulty and has been replaced.Thats why I am questioning the air theory?

I have been told by a leak check company who were very helpful I should get a pressure test done and the pressure guage checked before getting them out as they will be expensive does anyone have any ideas of further things that can be checked by a DIY person as the gas company arent interested in coming back out at the moment until the system breaks down entirely.

I am trying to do something before that point! We have been told by the leak co. we will have lost over 100L of water now surely we would of seen some evidence somewhere?

 

[ChrisR]

We have also ballooned the overflows and although one has inflated slightly with air

Eh?
Sealed systems don't have ANY overflows.
They have ONE pressure relief pipe which goes outside.
Do you mean automatic air vent(s)? If so where?

 

[DiyAngel]

sorry not making myself clear I put a balloon over the water release valve PRV? downstairs(from the boiler) and we have another air valve in the loft as well and also then I went the whole way and stuck them on the overflow valves from the hotwater cylinders.It was one of these that inflated slightly with air. The hot water system isnt sealed.Does that help. I know the systems shouldn't interact but I wonder if we have a possible leak from the coil in the cylinder and that is why we arent seeing the water loss. Although I have been told that is not possible because we are not getting brown hot water from the taps. Do you always get discoloured water if there is a coil leak?

 

[Andy165]

If the coil from the hot water cylinder was leaking, the cws tank would most likely over fill and you would get water coming out of your overflow pipe

 

[gas_man_gaz]

what boiler make at model? if its condensing it could be the h-ex leakin and escaping form the condensate..

who was the big gas company jus out of curiosity?

 

[DiyAngel]

Hi
Thanks for the idea but:
Its not a condensing boiler- sorry.
Certain gas company is the one thats just announced record profits after increasing their prices. I am one that pays a lot of money for cover, that they then wriggle out of sorting the problem out. Which is why I am asking for help on here. They think I really want to dig up all down stairs to trace a possible leak. When I have been told by the leak tracing company that there may be other things to check first like putting on the balloons and pressure testing and some how test the gauge to see if that may be giving a faulty reading. But if they say it must be a leak and it must be under the concrete floors, they wriggle out of doing anymore checks and we are left having to dig up floors or replace all the piping downstairs. So any ideas would be extremely helpful as money is an issue at the moment and we dont want to put it on our house insurance as you only end up paying for 5 times over, when they bump your premiums for the next 5 years.
Does it help any if I have noticed that the pressure drops if the heating is on or not. It still drops a 1/2 bar every 12 hours.

 

[DiyAngel]

Just read elsewhere that losing air through the automatic air release valve could make pressure drop. Does anybody know the answer if that statement is correct. I assume that the valve on teh top could go faulty???

 

[ChrisR]

Yes but you have to have air in there to lose. Usually it would be corrosion produced-gas, but systems CAN suck in air in strange ways.

Diagnosis is "simple"! You disconnect the boiler, and pressure test your pipes. obviuosly not trivial to do, but not insurmountable. As a first test, when the boiler's off and cool, shut its isolation valves, overnight, say. During that time you couldn't use it.
In the morning you check the gauge, open the valves and see what happens to the guage, and you have your answer IF the valves don't let-by, or leak.

Not surprising your balloon on the HW system overflow expanded - things getting hot DO do that!

 

[DiyAngel]

We have air in the system from the expansion vessel and valve replacements. The system was bled by the gas co. before they left and we have bled the rads. twice since-not getting out much air. But the system is still noisy as if air is in the boiler.
You said look at the gauge and see what happens but what would you expect to see either way with a pipe leak-no pipe leak? Th reason why I ask is the gauge drops if the heating is on or not and if the hot water is on or not, and it always drops by about the same amount 1/2 bar in 12 hours.

 

[Meldrew's mate]

Try ChrisR's tests.
Start, say, at 9pm
Boiler OFF for 3 hours - what's the pressure at midnight?
Shut BOTH boiler isolation valves. Wait 6 hours. What's the pressure at 6am?
DON'T TOP UP.
Open the valves. If the pressure shoots up it's a boiler leak, conversely if it falls there's a system leak (rads, pipes, cylinder). It all depends where the pressure gauge is - on the boiler or elsewhere on the system!

For 100 litres I'd go for the cylinder option, but don't expect to see coloured water unless the heating water is black with sludge!

Assuming boiler on ground floor and CWS tank in the loft the system pressure should not fall beyond about 0.1 bar if the cylinder coil is leaking, so try not topping-up for a day or two.

Mm

 

[superdupergasman]

What make/model of boiler is this??

How often are you repressurising??

If its a leak under ground floor then there will be no evidence.

And similarly could be a heat exchanger and the water is evaporating.

Leaks are hard to find, sometimes you have to use internal leak sealer which works a treat!

 

[DiyAngel]

Thanks for the suggestions
When the gas man emptied the boiler/system using the prv the water came out slightly discoloured with a hint of green. But it certainly wasn't dark. You may well be right about the cylinder as the pressure hasn't dropped below 1 bar if I forget to top it up. But when it drops to 1 bar the second cylinder doesnt heat properly- funny enough this is the cylinder that had the problems with overheating(ran dry like a kettle)had steam out the hot tap! then needing the new motorised valve and ball valve in the first place. I did ask at the time if it is possible that the cylinder had a leak as it is very noisy with air and the water movement in it isnt constant but comes in rushes.(this is when it isnt filling) This was also the cylinder that the gas man put internal leak sealent in, how I dont know I wasnt there at that moment. Can you also reconfirm that if it is a coil leak you dont have to get dark water in the hot water supply, which is what I was told by the gas man.