Leak in Heating system

obriendj · 19-03-2026 11:15AM #1

Hi there

Am looking for anyone who may have had a similar issue or any advice that can be offered.

We have a leak in our heating system. the pressure drops from 1.5 bar to 0 in less than 2 hours
We have had a local plumber look at it - he did try a thermal camera but eventually suggested a leak specialist
We got a leak specialist out and they spent a few hours before finally finding a very small leak.
they recommended we get those pipes replaced.

We did that and at the same time added some valves to allow us to "zone" our heating..
We are not able to isolate half the radiators.
In one half of the house the pressure does not drop, while in the other the pressure drops very quickly.

We have still not found where the leak is but are getting by.

One option is to get another leak detection done. but one plumber suggested to run fresh pipes again, trace via the walls but the estimated cost is 10k+.

Any thoughts or recommendations?

thanks

10-10-20 · 19-03-2026 12:45PM

Hi, did the leak detection company indicate what the likely cause of the leak was in the first case? That would be interesting to know as it would give you direction as to whether you had two isolated issues, or an endemic issue - such as systematic pipe corrosion.

I'd be leaning on getting the leak detection company back (they might do a reduced fee for a repeat) as that's your best option in terms of understanding the extent. I would not move forward otherwise.

Wearb · 19-03-2026 03:02PM

Copper or pex? Pipe leak or a join? How old is the plumbing? Heating system, oil, gas, back boiler?

obriendj · 19-03-2026 03:25PM

https://www.boards.ie/discussion/comment/124324489#Comment_124324489

mainly copper, newer rads were added and would have been pex
not sure about the leak location so could be either pipe or a join.

house was built in the 90s - using oil heating system - oil boiler was replaced in 2019.

most pipes are in the solid wall or floor. what i did dig up around the suspected leak area, there was no insulation. with plastic bags in and around the pipes.

obriendj · 19-03-2026 03:30PM

https://www.boards.ie/discussion/comment/124324127#Comment_124324127

Thanks for this.
the cause was most likely to do with the pips being in cement and was down to wear on the pipe near a join.
they were here for a good few hours and it did seem like a pinhole but I do think there is a bigger leak somewhere.

The other issue was that it was months for them to be available to call out. like everything these days.

ongarite · 19-03-2026 03:33PM

you could try the perfume method, trick to at least narrow it down to a room.

Top up system through radiator or fill tank with some perfume & run the heating for a while. You should be able to smell it in the general area unless it’s deep in wall or solid concrete floor.

Deep Thought · 19-03-2026 03:39PM

we have had the same problem.

Plumber can’t find anything, the amount we were loosing he said we should see it somewhere.

all out rads drop down so if it was upstairs we would see it on ceiling, if downstairs we should see it on floor.

We were topping up twice a day. We added some sealer and it seems to have slowed right down. 6 weeks gone since sealer and no top ups yet.

All but one room has qualpex piping, and We are getting some remaining copper and old rads in remaining room replaced soon .

We can only assume that they may be an old pipe going ground somewhere.

Escapees · 19-03-2026 03:54PM

https://www.boards.ie/discussion/comment/124324667#Comment_124324667

And presumably the leak is not within the boiler itself or via a pressure relief valve. For closed systems, bear in mind that expansion vessels are know to fail over time, although this would usually be noticeable via a 'leak' from the pressure relieve valve, usually at the boiler.

obriendj · 19-03-2026 04:23PM

https://www.boards.ie/discussion/comment/124324667#Comment_124324667

Yes we did try the sealer option but didnt help
glad it sorted yourselves out!!

10-10-20 · 19-03-2026 05:53PM

I'm starting to like the sound of the perfume trick on this one.

winklepicker2025 · 19-03-2026 06:32PM

safety valve on boiler dripping ?
expansion vessel perhaps gone ?
open vented system or sealed system ?

Deep Thought · 19-03-2026 07:59PM

https://www.boards.ie/discussion/comment/124324725#Comment_124324725

correct, checked PRV, expansion. Boiler is 18 months old.

We reckon over the period of time we were topping it up, prob couple of hundred litres vanished.

That level of water loss would be very visible if internal

obriendj · 19-03-2026 08:42PM

https://www.boards.ie/discussion/comment/124325132#Comment_124325132

the safety valve was replaced

The expansion vessel seems to be working as expected

It's a closed system

But I think the valve and vessel are OK because the heating works when we turn off half the house.

Escapees · 19-03-2026 11:18PM

https://www.boards.ie/discussion/comment/124325010#Comment_124325010

Or rather the smell of it, so long as the OP picks a fragrance that's tolerable!!

I think a couple of assumptions can be made at this stage, based on the apparent size of the leak. One of these is that it is highly likely to be on the ground floor. If you can access the feed and return pipes that run between the floors, then you could in theory further isolate parts of the circuit via freezing each pipe and closing the valves on the relevant radiators (just make sure that some flow path is maintained if running the system!). The key thing here is that you don't necessarily need the heating on or even the circulation pump running to test for the pressure drop. Actually, there's a thought - are you doing all the pressure drop testing with the heating running or just with the system off? Would be interesting to see if you see a pressure drop with everything off but the zone valve open. Next thing to try would be with the circulation pump running but not the boiler, so no heat expansion effects. And then maybe try increasing the speed of the pump if an option as this will likely result in a quicker pressure drop from any leak.

obriendj · 20-03-2026 10:50AM

https://www.boards.ie/discussion/comment/124325796#Comment_124325796

Sorry i should have stated - we are in a bungalow so its definitely on the ground floor. :)

Originally the issue would not occur or be as obvious, when the heat was off. but we have since had pump replaced so will do further testing over the weekend.

The new pump itself does have a 3 levels of speed so will try your suggestion.

good point around the perfume smell.

Thanks

Escapees · 20-03-2026 03:42PM

https://www.boards.ie/discussion/comment/124326384#Comment_124326384

Ah, when you said about zoning each half of the house, I thought it was odd alright that you'd be combining upstairs and downstairs rooms in a 2 story house! Just figured you might have a fancy house with some living areas upstairs with a view!

Another assumption I meant to say earlier was that it's most likely that the leak is from a pipe joint or connection. Given that most of these would be in the proximity of the radiators to tap off the main feed and return lines, it might be an option to pull up the vertical pipe insulation sleeves below the radiator valves without removing the flooring or at least with minimal interference. This 'might' be a relatively easy way to get an indication of any water leaking in the immediate area.

10-10-20 · 20-03-2026 04:08PM

https://www.boards.ie/discussion/comment/124327184#Comment_124327184

It may be a solid floor:

the cause was most likely to do with the pips being in cement and was down to wear on the pipe near a join.

Or the pipes might be on a raised floor, but sitting on knee-walls on the subfloor. Nevertheless, I'd still be getting the leak detector back with their magic gas and detection equipment.

Cerco · 21-03-2026 03:13PM

https://www.boards.ie/discussion/comment/124324809#Comment_124324809

Which sealer did you try? I resolved a leak with Tec7 plumb leak sealer. IMHO it is worth a try unless you already have.

Leak in Heating system

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