Central heating losing pressure

[Mississippi Bullfrog]

A couple of weeks ago I noticed our central heating system had lost pressure so I topped it up. The next day I checked and it was reading zero again so I topped it up a second time. That seemed OK for a couple of days, then it lost pressure again. Today I've had to top it up 4 times so there must be a leak somewhere - but there's no sign of a leak anywhere either inside or outside the house. If it was in the pipework between the floorboards I'd expect to see signs of a leak through the downstairs ceiling.

It's a combi boiler on a sealed system. We have a pressurised hot water tank but there's no sign of a leak from that and it's on a different pressure vessel anyway.

There is a pressure vessel for the central heating from which there's no signs of a leak but I wonder if an internal problem could cause the pressure vessel to take in the water from out of the pipework?

Any clues where to look next?

[NeilM]

Check your PRV valve.

It should be located beneath the combi and route to the outside of the house.

[Bender]

What boiler is it?

Water is leaking some where.

Check the blow off pipe has no water coming out of it via the property, if it is leaking the expert tank could be faulty, usually easy to tell as if you put heating on full the pressure gauge on the boiler will go upto and over 3bar, that's when prv opens, sometimes the prv refuses to seal properly once opened so may cause small constant leak.

You may have a small leak on the radiators or pipework.

Next up and more expensive if you have a condensing boiler, depends on make. The main heat exchanger/heat engine can become porous, as its condensing you don't notice water as it will drain away via the condensate.

[Mississippi Bullfrog]

Thanks - it's a Worcester boiler, probably about 8 years old.

I've checked all the radiators and pipes and there's no sign of a leak anywhere. Nor is there any sign of water from the pressure relief valve. Looks like it might be the heat exchanger then.

Ah well - just right time of year for the heating to pack in!

[Joe85]

Check your expansion tank, on most modern combi boilers its behind the boiler but it can be a separate unit either next to or above the boiler, sometimes in the loft.

If the expansion vessel bladder has ruptured or the air side has lost its charge, hot water cant expand into it and it will lift the PRV causing the system to lose water.

[megawatt]

Also check the shraeder valve underneath the red pressure vessel. If you press the centre of the valve and get water out, the bladder is leaking.

[Bender]

Unlikely to be heat ex on worc, what model is it so I can look at model.

Easy to tell if it's heat ex, you will have water constantly dribbling out through condensate when boiler not on.

You will have isolation valves on heating flow and return, top up boiler to 1.5bar, turn off both valves and leave for as long as you can, if it's the boiler the pressure will drop and you know its not the heating as its isolated.

If pressure stays the same open either valve, if the radiators have lost pressure you will see gauge pressure going down as you open valve.

[Mississippi Bullfrog]

The boiler is a Greenstar 30CDi. The condensate pipe runs down the back of the kitchen unit so I can't see where it leads to without taking the whole thing to bits. However the condensate pipe is warm to touch - I've got a feeling it shouldn't be?

The expansion tank is built into the back of a kitchen unit and sits right on the floor, I can't see any valve on it but it's been there since the early 1990's so far as I know.

[Bender]

Will have a look later, the tank will be built into the boiler, the one under the bench maybe an old one or the system is too large for the tank on the boiler, turn off the valves on the boiler, if it's the boiler it will loose pressure quickly.

If the expansion tank has gone you would see water out the relief pipe outside and the pressure gauge on the boiler will go very high.

[Mississippi Bullfrog]

Well the boiler is off and there's water dripping from the condensate pipe.

[NeilM]

It's not I imagine a condensate pipe.

That's the relief line. The one attached to a pressure relief valve yea?

The condensate line will be 4mm plastic.

[NeilM]

The expansion tank in the kitchen unit could be for a separate or as said old system.

The Worcester you have definitely has a built in expansion vessel. If you take the lid off the top you will see it.

[megawatt]

Could prv be passing Neil?

[Mississippi Bullfrog]

The pipe that is dripping is a 10mm plastic pipe plumbed into the washing machine drain.

I'm pretty sure the pressure relief pipe is a copper one.

There's no expansion tank inside the boiler, I've got the installation schematics for it. The installation diagram has an external expansion tank specified.

[Mississippi Bullfrog]

Just rechecked the installation diagram - it's definitely the condensate pipe that's dripping.

[Bender]

It will drip if you have the heating on, have you checked it with heating and hot water off and isolation valves which are built into the connections on rear where heating pipes go.

Condensate will be plastic and should be same size as overflow from water tank or toilet 20mm is, or pipe will be copper and should exit on the outside wall usually directly onto the wall.

[Bender]

The pipe that is dripping is a 10mm plastic pipe plumbed into the washing machine drain.

I'm pretty sure the pressure relief pipe is a copper one.

There's no expansion tank inside the boiler, I've got the installation schematics for it. The installation diagram has an external expansion tank specified.

 

Just dl the cdi combi manual, the expansion tank is no 26 its on the left hand side of the boiler?

[Bender]

If it is the main heat exchanger worc cover them for 10years if they don't try and wriggle out of it.

[NeilM]

Could prv be passing Neil?

 

That's what I'd always look at first.

[NeilM]

The pipe that is dripping is a 10mm plastic pipe plumbed into the washing machine drain.

I'm pretty sure the pressure relief pipe is a copper one.

There's no expansion tank inside the boiler, I've got the installation schematics for it. The installation diagram has an external expansion tank specified.

 

Just dl the cdi combi manual, the expansion tank is no 26 its on the left hand side of the boiler?

Try n post the schematics up n some pics.

I'm with Bender on this one. The expansion should be built into the unit.

Unless somones added to it?

[Bender]

It's on the left hand side of the boiler it's a tall thin sideways mounted one, if your looking for a big round one you won't see it.

[Mississippi Bullfrog]

The pipe that is dripping is a 10mm plastic pipe plumbed into the washing machine drain.

I'm pretty sure the pressure relief pipe is a copper one.

There's no expansion tank inside the boiler, I've got the installation schematics for it. The installation diagram has an external expansion tank specified.

 

Just dl the cdi combi manual, the expansion tank is no 26 its on the left hand side of the boiler?

 

The components diagram goes up to item 23. The left hand side of the boiler is an empty void.

I'll get our usual chap who installed it to check it out, just hope it keeps going if I keep topping it up.

Thanks for your advice and help.

[bonio]

Sorry to hear of your woes [mention]Mississippi Bullfrog[/mention]. I feel your pain: our old boiler packed in just before Christmas, so the house got an unexpected early Christmas present. Better luck to you, mate.

[Mississippi Bullfrog]

Google shows several versions of the boiler, some with the expansion tank internally and others like ours with a void where the tank goes.

[Bender]

Is it def a combi. Even on the system boiler it's no 23, I don't know of any worc combi that doesn't have an expert tank.