Leak in central heating system - advice please

[moonmonkey02]

system is leaking but can't trace it - please help!

we have an oil boiler (pressurised system but not condensing boiler) located outside against the house.

over the last 3 or 4 days its losing all pressure within a few hours of being topped up - this equates to a couple of the radiators being virtually drained and being filled up again by bleeding them - it's always the same radiators. when topped up the heating and hot water work perfectly ok.

this morning the boiler wouldn't work at all until the system was filled - i presume there was no pressure in the system to safely operate the boiler. once filled it worked perfectly ok.

its losing pressure even when the boiler is not on: i.e. turn heating system off and it still loses pressure.

now with this amount of water loss i would have expected to be able to see signs of a leak but can't see anything anywhere.

i'm not a plumber but not a complete numpty either having dealt with a few minor leaks on radiators and we have had a couple of pressure valves go on the boiler itself which have been sorted out. the boiler has always been serviced annually and any issues dealt with by a proper bolier engineer.

i've even had my father-in-law have a good look (a very experienced builder) and he can't see anything either so i don't think we're missing anything.

this time the leak has got me as i can't seen anything within the house or in the boiler.

searching the net (and on here) i underdstand it could be the expansion tank in the boiler - i would have thought if this was leaking i would see water inside the boiler? or where would it go?

any advice greatly welcome.

 

[Alpha man]

Could be leaking from the boilers PRV or AAV, has it been serviced recently?

could be something simple as a weaping rad valve!

 

[moonmonkey02]

checked the PRV and AAV and these appear to be ok - both of these have been replaced in the past. if these were faulty i would have expected to see water on the top of the boiler. i checked these when the boiler was cold (overnight) and there were no noticeable leaks.

i've also checked the rad valves (also done this before) but found nothing.

i would have thought with the amount of water loss, especially when the boiler hasn't been on, a leak would be noticeable.

one thought i did have about the expansion vessel, i can remember the service before last the engineer removed it and pumped water out of it before reinstalling - is this right?

boiler was last serviced in march this year.

 

[Centralheatking]

No obvious water leak and repeat pressure drop. usually the prv or exp vessel. sounds like
the exp is full of water. If your not competant get a GS engineer in.

Do not attempt to re-pressurise the exp. yourself. It you get it wrong you can cause an explosive leak of very hot water anywhere on the system. A child was scalded to death in their bed in this way with the leak happening over their cot 18 months or so ago

centralheatking

 

[moonmonkey02]

i'm going to check the expansion vessel tonight.

am i right in thinking press the valve and if water comes out it could need replacing and also feel if its got water in it?

wouldn't do it myself: how much very roughly to replace the expansion vessel. it a grant vortex combi?

 

[mountainman]

i'm going to check the expansion vessel tonight.

am i right in thinking press the valve and if water comes out it could need replacing and also feel if its got water in it?

wouldn't do it myself: how much very roughly to replace the expansion vessel. it a grant vortex combi?

If you press the valve and water comes out then the vessel Will need replacing.
The only problem with you touching the vessel is if it doesn't need replacing you have effectively reduced the charge in the vessel and this could lead to other problems.

 

[moonmonkey02]

i think its one of those that you can pick up and hold whilst still attached by a flexi pipe - so if i pick it up and its got water in it (heavy) i presume this is not good? or can i tap it and see if its full from top to bottom?

 

[Centralheatking]

I often wonder that ....
(if the expansion vessel which is located at the back of the combi boiler
and will be a special part for each boiler - and expensive) is stuffed.

Would it be better/cheaper to go get a separate exp vessel and just tee it in
somewhere convenient. These Exps are often much cheaper

Or am I being a yob ???????? centralheatking

 

[TBServices]

I often wonder that ....
(if the expansion vessel which is located at the back of the combi boiler
and will be a special part for each boiler - and expensive) is stuffed.

Would it be better/cheaper to go get a separate exp vessel and just tee it in
somewhere convenient. These Exps are often much cheaper

Or am I being a yob ???????? centralheatking

I do this all the time, space permitting.

 

[mountainman]

Sometimes a Robokit (odd name eh!) is by far the best option.

 

[nowucit]

If the system is being topped up to this degree would the PRV not start to show after a few top ups?

presumably once the expansion vessel has reached it's internal capacity the water would then need to go elsewhere?

 

[jtsplumbing]

If you cant find any water leaks at all and looseing the amount you say, i would be thinking about the main heat exchanger ! are you sure that you have no leaks under the floor ?

 

[leethegasman]

i'm not a plumber but not a complete numpty either having dealt with a few minor leaks on radiators and we have had a couple of pressure valves go on the boiler itself which have been sorted out. the boiler has always been serviced annually and any issues dealt with by a proper bolier engineer.

i've even had my father-in-law have a good look (a very experienced builder) and he can't see anything either

Think it's time to call in your Boiler engineer as it looks like you have done as much as you can hope he or she sorts it out for

 

[dancinplumba]

its an oil boiler

 

[dancinplumba]

No obvious water leak and repeat pressure drop. usually the prv or exp vessel. sounds like
the exp is full of water. If your not competant get a GS engineer in.

Do not attempt to re-pressurise the exp. yourself. It you get it wrong you can cause an explosive leak of very hot water anywhere on the system. A child was scalded to death in their bed in this way with the leak happening over their cot 18 months or so ago

centralheatking

this was a cws cistern

 

[nowucit]

this was a cws cistern

i remember reading this very sad

BBC NEWS | England | Somerset | Focus on baby death safety checks

 

[leethegasman]

its an oil boiler

Cheers have changed post

 

[Crazylady100]

I have just seen this old thread as I have been having similar problems with my boiler losing pressure and the boiler engineer couldn't find where the leak was. We thought it might be under the tiles in the hall but the last thing I wanted was to start ripping the floor up to find the leak with all the expense and disruption that goes with that.
It turns out that the cost of finding the leak was covered on our insurance policy under what they call Trace and Access (trace the leak and access it). There are companies that specialise in this work and they find the leak by using a special heat camera and by introducing a special gas to the system which they then sniff out with a detector. We used a company called The Leak Team and they were able to pinpoint the leak to a pipe under the corner of the lounge, which is carpeted and therefore easy to pull back and fix. Much less disruption than hacking up the hall tiles and they found the leak on the first visit, which was such a relief after all the tooing and froing we had had already with plumbers etc.
I recommend that you check your insurance policy to see if you are covered for this sort of work. Having said that the company I used were so confident they would find the leak they said there would be no fee if they couldn't!

 

[Dotty]

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