Leak in heating system

[Redhound]

My oil central heating system has sprung a leak. I have been topping up the water pressure loop several times a day. When I got the plumber out he has checked the boiler/expansion vessel (all OK) and diagnosed a leak of unknown origin somewhere in the house. Upstairs has been ruled out as no water coming from the ceiling, nothing obvious downstairs but it is mostly tiled. Two downstairs rooms have no radiator connected, but that still narrows it down to several tiled rooms with no obvious signs of water escape. Plumber (very experienced) seemed to think that all I could do was leave it and wait for signs to show weeks or months later! Is this my only course of action or has anyone any other ideas!? Thanks

Systems are most likely to leak at the connections. You can view all the connections on the radiators to check they are ok.

There are usually some buried connections as well where the system is most likely to leak, but where these are depend on your system.

I would say if you are topping up your system a few times a day then the leak has got to be fairly serious, although because systems are closed it does not take much additional water to increase the pressure. It might only be a couple of litres of water or so per day. Still that should mount up and eventually become visible.

You have the additional problem that you are diluting the inhibitor if you are topping it up on a regular basis as well.

I think nearly all the systems I have heard of where there are major leaks that are not visible it has ended up being the expansion vessel. Have you checked the overflow pipe from this to see whether it is dripping ?

Are you finding any single radiator that seems to be filling up with air ? That might give you a clue where the leak is located.

Following for some wisdom as we are in a similar situation. Topping up the heating once every other day... Boiler and expansion vessel both checked and no pools of water anywhere but we also have underfloor heating and a pressurised hot water tank to add to the issue.

This happened to us with a gas boiler and it was the boiler itself that was the problem. There was no obvious leak

OK one idea, get some humidity meters and put them in all the rooms. Keep the doors to all the rooms closed as much as possible - if there is a leak in or close proximity to the room the humidity should be increased in that room.

@BoTimic Cracked heat exchanger maybe ? I guess if the boiler is on a lot then it's possible the water leaking out just evaporates off hot surfaces internal to the boiler.

We had this and our problem was located in a cavity wall so leak was hidden, we were recommended to put some cheap stinky perfume into the tank and follow the smell when it leaked out !

Thank you for the suggestions. Plumber has definitely checked the expansion vessel (which is a fairly new replacement) and the overflow pipe (not dripping)
That is a good idea about a humidity meter I will try that thanks.

OMG the perfume idea! I will see if that is feasible!

The other thing I have used is an FLIR camera in the past.

These detect hot spots. So if you have hot water leaking in an internal wall you might be able to pick it up as a hot spot.

They are not cheap to buy though, but if you know someone with one you can borrow it - they can be useful for all sorts of stuff as well as leak detection. You can find leak detection tutorials on youtube.

That's a good idea. Might try that.

The damp meter thing won't work for us because we have do damp proof course and some of the rooms have ongoing non resolved damp issues at the moment.

Leak detection - used to work in home emergency insurance, a leak detection team will save a lot of time, money and potential damage, we used them all the time for leaks downstairs under tiled flooring/concrete.

Do you have a "plume" of steam coming out of the flue at any time? If yes, I would suspect a cracked or corroded heat exchanger. Oil boilers are known for back end corrosion if the return temperature is too low.

When you find out what it was please update the thread.

Thanks for the further ideas, they are great. I will certainly update when I can!

Are any of them near a radiator pipe?

@PigletJohn No. The issue is the guttering but it is a bit complicated to fix because the house is listed so we need to keep the old wooden stuff. That means I haven't worked out how to change the angle to make it slightly steeper. We thought we had fixed it and it is fine if the rain isn't too heavy but overflows when there is heavy rain. Next job on the list is to check that a hopper at the top of the drain isn't blocked but it's a bit high up (10m) and I am not great with heights so am putting it off.
Nice to see you back posting stuff again. You have been quiet for a while. Hope you had a nice Christmas.