Heating System Keeps Loosing Pressure

crosstownk

Howdy all. Hopefully someone might have an idea.......

I've a sealed gas fired heating system. It's been running fine for 4 years but lately it is constantly loosing system pressure. I top it up via the filling loop - usually to about 1.2 bar as that's all that mains pressure is providing these days

Within a few days it drops back to 0.8 bar at which point I top it up again. Obviously I've a small leak somewhere but I can't find it anywhere. I've check radiator fittings, all visible pipework, boiler, etc, etc.

Any suggestions? Should I just put some leak fix in and see what happens or is there some other way to identify the leak?

BTW, I always check system pressure only when the system is cold.

shane0007

It could be expansion vessel failure. Check the exit pipe from the prv outside. See if it is dripping or wet.

crock!

It could be a small leak either but lets hope its the vessil that needs to be charged. This could be done on a service

crosstownk

Thanks, Shane. The PRV appears dry. How can I verify if the expansion vessel is working correctly?

shane0007

If the vessel is part of the boiler, then it needs to be done by an RGI as the boiler needs to be drained to check.
If the boiler is due a service, it is part of the service to check so at least the boiler can be eliminated if the leak is external to the boiler.

crosstownk

I've an Ideal ICOS which I think has an expansion vessel integrated. I've also an expansion vessel in the attic close to the filler which is left over from the previous system.

Service is due next month so will start there.

DGOBS

If the PRV is dry, would not be the expansion vessel. from 1.2 to 0.8 bar of a leak is a small amount of water, and if the prv was lifting the drop would tend to be higher than that.

Check all your rad valves and joints in the hot press etc for signs of leakage, but again given the small amount it would quickly evaporate on a warm system

crosstownk

I've just discovered and released an airlock in an upstairs radiator. This has dropped operating pressure down to 1.2 bar until I top it up next.

Is it possible that this airlock may have some part to play in my pressure loss?

shane0007

Could be leaking from the pipework serving that radiator so that would be my first area to imvestigate.

jeepers101

I've never understood how a leak in a system charged to over a bar can cause air to get in.

shane0007

jeepers101 wrote: »

I've never understood how a leak in a system charged to over a bar can cause air to get in.

Erm... is topping up the system not bringing fresh water back into the system and therefore re-oxygenating the system?

crosstownk wrote: »

I top it up via the filling loop - usually to about 1.2 bar as that's all that mains pressure is providing these days
Within a few days it drops back to 0.8 bar at which point I top it up again.

jeepers101

shane0007 wrote: »

Erm... is topping up the system not bringing fresh water back into the system and therefore re-oxygenating the system?

Why check the pipework of the air-locked radiator first?

spireland32

jeepers101 wrote: »

Why check the pipework of the air-locked radiator first?

Tricks of the trade as the fella says

shane0007

Water leaking will usually affect the nearest radiator above the leak first as it will take water from that first.

jeepers101

shane0007 wrote: »

Water leaking will usually affect the nearest radiator above the leak first as it will take water from that first.

Do you mean the radiator will take water from the topped up water first?

shane0007

Where else will it go unless it air locks? It will hardly go to a rad full of water already!

jeepers101

Yeah but the the water is flowing around in a loop no? And the top up is connected to the return so it goes to the boiler first and then follows the circuit around.

If there is a leak from a rad, the general system pressure is reducing but the rad is still full of water. Until that is the pressure reduces to atmospheric.

Still can't get my head around it.

shane0007

The water is only flowing round a "loop" when the circulator is on. Gravity, I'm afraid, always goes downwards. If there is a crack/opening in a joint/pipe, gravity will take the water above it downwards and out through the opening. Some radiators will not loose their water, sort of like holding a bottle of water upside down can hold the water within it. It's just one of those things that allows us to come up with wonderful phrases like "it's not a perfect science!"

Who said anything about the filling loop being connected to the return? It can be located anywhere on a pressurised heating system!