How to check if heating coil is leaking?

tevion

Heating system is losing pressure.
Its a 17 year old house with a gas central heating system.
Goes from 1.2 bar to about 0.5 bar after 2-3 days.
Have checked the PRV in the boiler and have checked all visible pipes/radiators for leaks and cant find anything.
I think it is down to two things, either a leaking pipe under the ground somewhere that I cant find, or possibly the heating coil in the hot water cylinder is leaking?
The hot water cylinder is probably as old as the house, one of the old copper ones that you have to put a lagging jacket around.
Before I go to the expense of changing the hot water cylinder, how can I check if the heating coil is actually leaking, to be sure first?
Is this a common problem for a heating coil to leak, or is it more likely to be a leak elsewhere?

kay 9

You could drain your domestic water from cylinder, leave your cf closed to it. Leave the drain cock open and see if it leaks. Only other way I can think of is drain cylinder, air test through the coils and listen for it. But be careful if doinng that, make sure your hot connection or cold is open first.
Ps. cylinder usually goes before coils as coils are heavier guage copper but it could be faulty brazing. Emmersions have known to cause minor coil leaks because of earthing on them and they get burnt slowly over time.

Forgot to add, the leak is more than likely elsewhere.

Sparkpea

you can usually see a swirl moving in your storage tank coming from the feed pipe to the hot tank. so if you look closely towards the tank connector at the inside of the storage tank and see something moving, even feel down towards it. make sure you are looking when no water is running etc. depending on how bad the leak is you may be able to feel it. it may be harder to know as yours is a pressurised system so I would top it up then go and look quickly.

saying that if its taking 2-3 days for the pressure to drop like that I wouldnt think its the coil. if it is the coil u might find your cold water storage water being a bit murky from dirt/rust/chemicals from the heating system mixing in you're bathing water. its probably a tear at a gland nut at a radiator valve or gate valve, even at the pump/pump valve, also check all pipes going in and out of radiators for tiny weeps.

Buford T Justice

Sparkpea wrote: »

you can usually see a swirl moving in your storage tank coming from the feed pipe to the hot tank. so if you look closely towards the tank connector at the inside of the storage tank and see something moving, even feel down towards it. make sure you are looking when no water is running etc. depending on how bad the leak is you may be able to feel it. it may be harder to know as yours is a pressurised system so I would top it up then go and look quickly.

saying that if its taking 2-3 days for the pressure to drop like that I wouldnt think its the coil. if it is the coil u might find your cold water storage water being a bit murky from dirt/rust/chemicals from the heating system mixing in you're bathing water. its probably a tear at a gland nut at a radiator valve or gate valve, even at the pump/pump valve, also check all pipes going in and out of radiators for tiny weeps.

Oddly enough, I went out to a job last week where there were two rad valves leaking in a kitchen. Closed System
When I was on the phone to them, and asked them the pressure, they said it was 1.5 bar, which is the way it was when I left it about a month ago. I said it had to be something else, as a leak would have de-pressurized the system and they didn't top it up. Went out and the valves were definitely leaking, but there was no loss in pressure whatsoever.

Thought it was a bit odd.

tevion

have checked all radiator valves, pipes, gate valves etc, and no sign of any leaks..
Any ideas what to do next?

kay 9

Faulty AAVs fitted anywhere?

tevion

kay 9 wrote: »

Faulty AAVs fitted anywhere?

There is just one automatic vent thing fitted beside the hot water cylinder, and that seems fine, no water around there.

Sparkpea

Just read over your post again, I think I would look elsewhere. I've only ever seen 2 coils leaking in my life and 1 was done through powerflushing a copperclad system. How often is it dropping? Every 2-3 days if you top it up again will it drop? I'm guessing its unlikely theres air in the system escaping from an AAV. My personal opinion would be a leak that you cant find underground.

The only thing you will gain from changing the hot water tank is by eliminating another option. If its not the tank and you replace it and its still dropping then its a waste of money. What about joining the flow and return pipes together so its not going through the coil for a few days and see if the pressure drops? Use the immersion (if they have one) to get hot water for a few days.

tevion

Sparkpea wrote: »

Just read over your post again, I think I would look elsewhere. I've only ever seen 2 coils leaking in my life and 1 was done through powerflushing a copperclad system. How often is it dropping? Every 2-3 days if you top it up again will it drop? I'm guessing its unlikely theres air in the system escaping from an AAV. My personal opinion would be a leak that you cant find underground.

The only thing you will gain from changing the hot water tank is by eliminating another option. If its not the tank and you replace it and its still dropping then its a waste of money. What about joining the flow and return pipes together so its not going through the coil for a few days and see if the pressure drops? Use the immersion (if they have one) to get hot water for a few days.

yeah the general consensus seems that its unlikely that its the heating coil thats leaking.
I top up every 2-3 days, and it drops back down again.
I am thinking of employing the services of a leak detector company that use thermal imaging equipment, as it seems that its most likely a leak under-ground from what is being said here.

Plombier

Check your expansion vessel if its burst the pressure can drop very quickly. If thats not it, dont replace the cylinder, disconnect the heating pipes from the coil, cap return to the coil, leave for 24hrs then remove the caps if there is water the coil is leaking.

tevion

Plombier wrote: »

Check your expansion vessel if its burst the pressure can drop very quickly. If thats not it, dont replace the cylinder, disconnect the heating pipes from the coil, cap return to the coil, leave for 24hrs then remove the caps if there is water the coil is leaking.

Its a new Worcester system boiler that was fitted recently, the old expansion vessel was removed, so I think the expansion vessel is now part of the boiler.

Sparkpea

tevion keep us updated, good to know how you get on