Leaking pipe and boiler pressure woes!

[valadon68]

Boiler pressure was going too high and also dropping about three weeks ago - an engineer replaced the PRV and it behaved angelically till today, when we woke up to a fault and no hot water. Repressurised and it's holding, so far. But have to reluctantly face up to possibility of a leak. No ceiling stains so thinking probably under suspended floorboards?

Has anyone had success with using a thermal imaging camera and moisture detector to pinpoint a leak themselves?
Or what have people recently paid for leak detection, if you don't mind sharing? Any advice v gratefully received! Loads of house maintenance to do and thought we'd put this prob to rest...

Could it be the expansion vessel ? Is water being released from the PRV ?

Expansion vessels are always a prime point for failure because they contain moving/perishable parts.

Possibly! There don't seem to be drips outside though & engineer said it looked ok (though mentioned it would be the next thing to check - that or a leak. Why he couldn't check it while we were paying £££ for a call out fee, not sure!). Thanks for the tip.

Whenever I have had similar issues, it's always been a problem inside the boiler itself, never random pipework elsewhere in the house. Expansion vessel & PRV needed replacing in my last Worcester Bosch (which was old).

....If you happen to be in the Midlands AND have a Worcester Bosch, just get them out directly. For £300 they'll basically rebuild the thing for you. Check out if your manufacturer offers something similar.

Oh thank you @bignewprinz ! That is heartening to hear. We have a really old (20 y.o.) boiler which is apparently more or less in good nick and no paperwork for it from old owners of the the house. But will see if there's something like that on offer. So have you had the same thing - sudden drops to below 1 bar? How often did it happen when it was an issue for you, if I may ask?

Boiler was doing an angry loud hum earlier on but has calmed down now. Have bled the only two radiators I can bleed with the tools we have (most radiators are very old) & no air in those, pressure didn't drop afterwards.

Leaks don't often tend to go away and come back again unless they are due to thermal expansion/contraction of the pipework. Once a leak happens the pressure within the system will normally ensure it is maintained.

Thermal imagers for finding leaks, I guess it is possible. I can see pipes under the wooden floor in my house with a thermal imager but whether you would be able to tell a leak or not is so dependent on the size of the leak and where the water ends up. Maybe run the system for a few hours at a high flow temperature to give you the best chance of finding it.

Have you bled all the radiators and re-pressurised? May just be air in the system.

Not much help I know .. but ..
We have months where our boiler loses pressure every few days (not fully but it starts to drop), then months where we have to bleed a radiator every few days to reduce the pressure
Then it’s fine for months!
Had several people out and apparently no issues
Just had the odd part replaced but it happens still regardless

"Boiler pressure was going too high and also dropping"

When an expansion vessel has lost air, it loses the ability to absorb the expansion of water when heated, and contraction as it cools. So the pressure rises above normal when hot, and falls below normal when cold.

If you top it up when cold, it is likely to eject water from the PRV when hot. This is not a fault in the PRV. That's what it's meant to do. You may not notice water coming from the relief pipe going through the wall behind the boiler and dripping outside. You may notice a mark on the outside wall or paving,

A pressure vessel can be pumped up like a bicycle tyre (it has a rubber balloon inside). In a combi boiler it may be an arduous job to replace it with a new one. Very often an external vessel is plumbed into a convenient pipe instead. It looks rather like a short fat gas cylinder. It can go anywhere.

p.s.

I don't think you've got a leak.

Thank you, everyone, appreciate it - and that's reassuring to hear from you, @PigletInABlanketJohn 🤩

Pressure is still holding perfectly so far. We had fun playing with a borrowed thermal imaging camera but it didn't map out the pipe network for us as we'd naively hoped. Relax till next time, I guess. Maybe we'll have to see about the expansion vessel eventually.

Omg, I read the title of your post and started feeling stressed. I guess you can imagine why!

A couple of year’s ago my friend’s boiler started loosing pressure. It had to be topped up every couple of days but she could see no sign of a leak, no stains on ceilings. The boiler was checked and the engineers concluded that there was indeed a leak somewhere. They used thermal imagining etc, did not find anything. They then drained the system and refilled it. The leak magically disappeared. No idea how but it was surely a leak given how often the boiler keeps being topped up.

Last year we did some refurbishment to the house and we interfered with/ touched the heating pipes. Woke up one morning to find the boiler pressure had dropped massively overnight. After a few weeks in which we kept topping up the boiler we called an engineer who confirmed the boiler was fine and this was definitely a leak. He said that using coloured gas etc will rarely show where the leak is, plus it’s expensive. So I started pulling my floorboards up to find the leak (luckily we didn’t have carpets at the time). I was so stressed. Eventually we found the leak under the floorboards in the bedrooom and fixed it! Boiler pressure restored to normal.

This year, the exact same thing happened. I woke up one day to find the boiler pressure dropped 😀. How can there be another leak?? Unfortunately, I had put new carpets down since the last leak, so I couldn’t pull the floorboards to check. As it happens, I had arranged to have one of my radiators replaced soon after that. This involved pipework and having the heating system drained and refilled. Since the system has been drained, my boiler is no longer loosing pressure. I don’t understand why draining and refilling the system fixes a leak, but try that!

How interesting @Gabitule ! Thanks for sharing these experiences - this is partly why I love MN, I hadn't come across this tip in my frenzied research anywhere else. Sorry to spike your adrenaline. Total amateur question, but when you started taking floorboards up, did you just stick to those near radiators? Wondering if they are mostly logical or can take non-intuitive paths.

I did notice a rusty valve on one which could potentially be more than cosmetically damaged, but not sure that is new. But then we are fairly new to the place ourselves.

To find the leaking pipe, we took the floorboards up room by room. We started upstairs. The pipes were mostly near the radiators, but also crossed rooms and the landing. When we pulled the floorboards near the radiators we could see where the pipes were headed and followed them. We found the leak in the 3rd room we checked. Despite the leak being very small, we had to top up the boiler every few days. The stainwouldn’t have shown through the ceiling for years probably, especially because in the winter the heated pipes dried the leak. But we were obsessed with finding the leak because we didn’t want to keep adding water to the boiler (a closed system, with anti scale etc) in case it damaged it.