Combi-boiler: Pressure loss

[athlk]

Hello all

I hope someone can help as we have been having a total nightmare with our boiler

Our boiler has been losing pressure now for the last few months, we have had several British Gas engineers round who have tried, putting sealent in the system (3 times), bled the radiators, checked for leaks inside the bolier and around the radiators but to no avail. We top the boiler up almost everyday although it seems to lose pressure faster when the heating is on rather when its just the hot water.

We have been told that it is probably a leak under the floorboards. Yesterday we spent the day taking up the floorboards and cannot see that any of the pipes are leaking. We were told that the amount of pressure loss would indicate a large leak and as such it would be obvious....we can't find it!

We are rather stuck as what to do next.....if anyone can suggest anything that would be great.

thanks

 

[Bernie2]

Is the boiler pressure release valve okay?

It may be okay at the cold pressure level, but what about at the higher hot level?

I assume though all that would have been checked by BG?

Some leaks only show when the system is hot and some only when its cold.

Have you looked with the heating in both modes?

Is the expansion vessel okay?

Is their a leak in the change over valve chamber?

Is the filling point nrv okay?

Loads of things to look for.

 

[stephens]

The company I use said they don't have to lift the floorboards, they pressure test between radiators in each part of the run till they find the run that is losing pressure. Then they know where to start lifting floorboards. If you are not on a service contract with British Gas and are paying as you go for repairs your best bet will be to ring around Heating Engineers to find ones that will find by pressure testing and ask their hourly rate before chosing. After all other things have been checked obviously. With a bit of luck you may find a good experienced engineer that will sort it for you. Best of luck.

 

[stevetheplumber]

if its losing that much its not going to be upstairs as it would have shown on a ceiling by now try putting the preasure up as far as it will go before the safety blows say 2.5 bar and listening you need to do this when its quiet often you can hear the leak especialy if you have some boards remove after that its isolate and preasure test
check all the radvalves for signs of leakage scale on tails etc

 

[dodgeyblade]

Have exactly the same problem.Also called out British Gas.He replaced the 3- way valve in the boiler which was leaking.Problem still exists.Wondering if the system needs bleeding or flushing out as there appears to be a fair amount of sludge in the radiators as the water was very dark when i bled the radiators a few weeks ago.

 

[newbie1]

check the pressure relief valve outside for signs of it having discharged any water if none then how much is it loosing it can be numerous things and really surprised bg havnt looked further
as regard being sludged then bg should have mentioned a powerflush as if it is then the new valve will only get sludged over time
best bet would be to check with system hot if its holding the pressure but prob needs a good engineer to go over it and pressure test the pipework

 

[so-solar]

Rip up as many boards as possible, up the pressure on the filling loop using the guage to about 2.5 bar, whack the heating on and trace the pipework! it has to be a leak from the downstairs pipework! The leak could be where the pipes are going through a cavity wall or tight in a corner but the only way to find this kind of leak is keep exposing the pipework until you find it. BG are not in a million years gonna start pulling boards up but if they are called to a leak then surely it is in the contract to find it and not try and repair a leak witout tracing it first!

Another way is to drain the system fully, connect an air pressure tester and a compressor and charge the system and listen for the air escape! remembering that the pressure relief lifts at around 3 bar!

Hope this helps

 

[heinz57]

Warning - if you do powerflush your system (and it sounds like it needs it) any scale or sludge that is partially covering the leaking hole may be removed making the leak ten times worse, this will make it easier to spot but could flood your house in the process.

 

[dodgeyblade]

Thanks for all the replies.

The pressure seems to hold when boiler not running.I will check the heating again over the weekend.I think the overflow pipe outside the boiler still drips ,though when in use,so the PRV could be the fault.Going to have a good look over the weekend.

Thanks again

 

[oldplumber]

ref stephens comments

Im at a loss to see how you can pressure test between rads in a normal circuit knowing that there is a leak somewhere, testing between the rads aint going to find its precise position as you can not isolate the pipes between the rads unless you cut in and isolate each section in turn. I think youve been had or met another plumbing bull******.

 

[Winston]

Hi Im not a gas enigineer but curious is the pressure dropping down to nothing? have you looked really carefully by all the rad valves/trv it doesnt take alot of water for the pressure to drop. I would be tempted to put the heating on and literally go round each rad examining carefully and bleeding the rads whilst you are there.

Once you have done all rads re-pressurise and examine all again, look at all the tails for signs of weeping old and new.

 

[NickH]

Im at a loss to see how you can pressure test between rads in a normal circuit .

My thoughts exactly.

This may seem a silly question but is it definately a combi boiler, you dont have a hot water cylinder ?

 

[stephens]

Originally Posted by oldplumber
Im at a loss to see how you can pressure test between rads in a normal circuit knowing that there is a leak somewhere, testing between the rads aint going to find its precise position as you can not isolate the pipes between the rads unless you cut in and isolate each section in turn. I think youve been had or met another plumbing bull******.

I wondered how this would work as the Rads are not in series. Hope I never get a underfloor leak on the ground floor if it cannot be done this way!
I will ask again when I next have it serviced, cannot remember which of their engineers it was though.

 

[dodgeyblade]

Hi again.
Checked the heating and I put it on two-thirds the setting on the boiler which took it to about 60-70 degrees.There is a drip from the boiler overflow outside about every two minutes.There's no drip when the hot water is running (50 - 60 degrees),but has lost a "needle width" in pressure over about 5 days.The hot water is only used for washing the pots ,though .It doesn't lose any pressure when not in operation.Could this be a faulty PRV ?

 

[newbie1]

pressure relief valve shouldnt be dripping give it a couple of spurts and see if it closes tight again

 

[Bernie2]

Sounds like pressure relief valve leaking. Has it got muck under the seating? As Newbie says, give it a blow.

But don't forget when you fill up with new water, the new water will have air entrained in it and over about a week or so you may very well get a slight to medium system pressure drop, until the water has given up its air through heating up and cooling down. Then you top up again until it stays steady. That is part of the reason boilers usually have auto air bleed valves

And don't forget you can entrain air from places in the system that don't leak water such as plastic pipe and loose valve packing glands.

 

[dodgeyblade]

Thanks for the replies.
Would I be better getting a registered plumber to look at it as I don't know the inside of a boiler or is this something I could do (drained system before)

 

[newbie1]

tbh its not a major job just a case of spotting it
it will either be a push or pull valve

 

[david williams]

ref stephens comments

Im at a loss to see how you can pressure test between rads in a normal circuit knowing that there is a leak somewhere, testing between the rads aint going to find its precise position as you can not isolate the pipes between the rads unless you cut in and isolate each section in turn. I think youve been had or met another plumbing bull******.

yes i was thinking that who was it reactfast seems like a good way to ramp up bill

 

[stephens]

Im at a loss to see how you can pressure test between rads in a normal circuit knowing that there is a leak somewhere...

yes i was thinking that who was it reactfast seems like a good way to ramp up bill

It was n't reacfast, just a local medium sized heating company. I only asked the heating engineer they sent (for a service) as I thought it must be a nightmare if I did get a leak and wondered if there was an easy way to fix. They have been OK so far and recommended by others locally.
I will ask again to see what the next one says (they have a few employees) as I am intrigued. Wish I could remember which one said it.

 

[Plumb tart]

pressure relief valve shouldnt be dripping give it a couple of spurts and see if it closes tight again

Thanks Newbie1 for mentioning " a couple of spurts" you have just solved a different problem I was having ...your a star cheers

 

[LIFES A GAS]

Not sure you have cured the problem, if the PRV was dripping all the time then you still would be losing pressure when operating water only. I would think the problem is caused by the expansion vessel, is the pressure rising on the gauge when the heating has been running some time? if it is and reaches 3 bars then the PRV will automatically open to release the excess pressure, this does not normally happen when running hot water even if the expansion vessel is not doing its job as the system water temp does not keep rising as it is transferred to the hot water via the water to water heat exchanger.
Hopes this helps Martin