Heating leaking

[cdbe]

It loses about a quarter of its 1 bar pressure over a few weeks. Only needs.a one second burst from the filling loop to bring back to 1 bar so not much loss. No visible leaks. It's ex open vented, now sealed, with a megaflo. Rads and pipework are a mix of new rads with new plastic pipework and 40 year old copper pipe and rads. I am repiping and replacing the old stuff as I work round the house but in the meantime is it likely that I'm losing a bit from the old parts and it's evaporating off?

 

[John D v2.0]

Check the charge in the expansion vessel or get someone to check it.
There probably is a small leak that's evaporating, but it sounds like the ev isn't taking up the slack.

 

[Iamchamps]

Check the pressure release valve. Wrap a small plastic bag round it and monitor over a couple of days to see if water is coming out of it.

Will be a pipe maybe looking a bit like a little mushroom some where on the outside of house.

 

[cdbe]

Hi, prv is dry, had a balloon on it.

I have a gauge so can check the pressure in the expansion vessel but can I do this with the system pressurised and what pressure should I be expecting? When I drained and flushed the system a few months ago it was pressurised to 1.2 bar - or am I just looking for air rather than water?

 

[Terry lambert]

The hello valve is interfering with the please actuator which has obviously cancelled out your thanks causing a drop in enthusiasm pressure to help

 

[John D v2.0]

Hi, prv is dry, had a balloon on it.

I have a gauge so can check the pressure in the expansion vessel but can I do this with the system pressurised and what pressure should I be expecting? When I drained and flushed the system a few months ago it was pressurised to 1.2 bar - or am I just looking for air rather than water?

drain valve needs to be open while checking.

Pressure should be below the cold pressure of the system so that the system water is partly in the vessel so it can expand and contract.

If your vessel has too much charge it will be full of air and therefore as soon as you lose any water the pressure will drop to whatever the height of your system is and the top rads will become dry.

 

[Terry lambert]

drain valve needs to be open while checking.

Pressure should be below the cold pressure of the system so that the system water is partly in the vessel so it can expand and contract.

If your vessel has too much charge it will be full of air and therefore as soon as you lose any water the pressure will drop to whatever the height of your system is and the top rads will become dry.

If my vessel is correctly charged and I lose system pressure, will my top rads become dry ?

 

[Terry lambert]

drain valve needs to be open while checking.

Pressure should be below the cold pressure of the system so that the system water is partly in the vessel so it can expand and contract.

If your vessel has too much charge it will be full of air and therefore as soon as you lose any water the pressure will drop to whatever the height of your system is and the top rads will become dry.

So if my system loses water and my expansion vessel is correct, my system will maintain a higher pressure than the head of my system ?

 

[John D v2.0]

If my vessel is correctly charged and I lose system pressure, will my top rads become dry ?

Of course! If your pressure drops below the heigh of the system your top rads will become dry regardless of your expansion vessel.
I said as soon as he loses any water at all, not as soon as he loses pressure.
If you lose water and there's some water in the vessel, the system pressure will drop slowly as you'd want, as the water is pushed out of the vessel as the air can expand.
If you lose water and there's none in the vessel, the pressure will drop quickly as the water in the vessel can't be pushed out by the air as there is no water there.

 

[John D v2.0]

So if my system loses water and my expansion vessel is correct, my system will maintain a higher pressure than the head of my system ?

Correct, and that's by design. but of course that only works until the expansion vessel is entirely filled with air.

Remember that the ops observation was that he lost pressure but hardly any water was needed to top it up. With a 10l ev I'd expect it to have a couple of litres in at cold 1 bar. That 2l is your backup against leakage.

 

[Terry lambert]

John, there too much wrong with the statements I havnt got the energy, I’ve got to go and fix some boilers.

Sorry I commented you’ll have to do some research and thinking about expansion vessels

 

[Terry lambert]

Also heating systems

 

[John D v2.0]

Hi Terry thanks for that but I'm not sure what the issue is?
Ev is 1.2 bar then you fill the heating to 1 bar, ev will be all air and the heating will be all water.
When you lose some small amount of water the ev will still be all air and the water will not quite be enough to fill the system. What will fill the space where the water was in the system?

 

[John D v2.0]

Ps I did learn about expansion vessel and all the material I read says charge the ev to a bit below cold system pressure. Presumably you have a reference somewhere that says it doesn't matter if it's higher, but I can't find it

 

[Terry lambert]

If your vessel has too much charge it will be full of air and therefore as soon as you lose any water the pressure will drop to whatever the height of your system is and the top rads will become dry.[/QUOTE]


Just one if the points I was trying to make above is that if your system loses water it will be replaced by air at the highest point of the system

This has nothing to do with the charge on your expansion vessel

When I go to a system and replace an expansion vessel in a boiler on the ground floor I drop the pressure out of the system, disconnect the vessel, the system now has no vessel let alone an incorrectly charged vessel

My rads on the top floor do not suddenly become dry ? They are still full of system water

You then fit a new vessel, check the pressure and re pressurise the system

Jobs a goodun

Edited for spelling