Finding a leak in a Central Heating system (water)

[sophiecentaur]

It has to be going somewhere!
The boiler pressure drops by about 0.5Bar every few weeks. I've looked at the radiators for signs of small leaks but I haven't been inside the boiler as yet because I only recently terminated a maintenance contract with British Gas. BG were not interested in a leak chasing exercise.

The techniques that I've read about include thermal imaging and gas tracing, both of which would involve buying equipment. I have heard of acoustic methods for detecting leaks in underground supply pipes but I bet that would need a healthy "hiss"; my leak must be a lot slower than that.

Has anyone in PF ever had and solved this problem? There are companies that say they'll do it for upwards of 65 GBP per hour but it can be a pretty open ended business, involving well over 1k GBP. I'd like to get better informed about it before shelling out on a process than must take a lot of punters for a ride.

 

[BillTre]

There might be a place you can rent a flir camera.
I know there are places to rent high speed cameras.

I also found a place to get paper sheets with a chemical in them for visualizing small water leaks. Might work with steam.

 

[jrmichler]

This is the leaky fitting in my boiler. The leak rate is about 0.5 bar pressure drop in 6-8 months. The gunk is from antifreeze in the system. Without antifreeze, there would typically be some mineral deposits. There would normally not be visible water. The antifreeze is because of the water lines running through the unheated garage to the air handler in my shop. The HVAC guy will fix it when he gets a chance.

Several years ago, my domestic water system had a leak. The leak rate was about 5 drops per minute, and roughly one gallon per day. That one was easy to find.

 

[sophiecentaur]

There might be a place you can rent a flir camera.

It would be possible but only one of the possible tools and I'm not sure that I could use it effectively. There must be a lot of 'wrinkles' to be learned about this business and I could waste a lot of time with one.

I believe there are thousands of domestic CH systems with small leaks and it's hardly surprising when you consider the number of joints in the piping around an average house. It could be argued that letting a few ml of water into the system is not worth worrying about, especially if the leak is somewhere where the water stays warm all the time and the water evaporates.

 

[Baluncore]

It has to be going somewhere!

Is there fluorescein in the antifreeze, or can you add fluorescein to the water ?
Use UV light before and after to look for the trace of a leakage.

 

[sophiecentaur]

Use UV light before and after to look for the trace of a leakage.

Problem could be that most of the piping is under floorboards.

Perhaps I'm asking the wrong question here. Perhaps I should be asking "does it matter enough to try to solve the problem?"

 

[Baluncore]

Perhaps I should be asking "does it matter enough to try to solve the problem?"

Not yet.
Keep an eye open for any greater problem, but avoid disturbing the system until something actually needs fixing.

 

[Rive]

Problem could be that most of the piping is under floorboards.

What kind of piping it is?

 

[sophiecentaur]

What kind of piping it is?

15mm copper, very basic afaics. It uses a hot water tank.

 

[Averagesupernova]

I'd like to know more about this system. I am assuming this is not steam heat and it is circulating hot water? An actual steam system there are no return pipes, water condenses in the radiator and runs back to the boiler in the same pipe, which BTW, I have never seen copper pipe in this system. Circulating hot water will certainly use copper. Any way you can isolate sections and deal with rooms that are colder than others? Watch for the symptoms to show up or not?

 

[Melbourne Guy]

I have heard of acoustic methods for detecting leaks in underground supply pipes

One of our water utilities is using vibration sensors in digital water meters to 'listen' for leaks, @sophiecentaur, but as far as I'm aware, it's a just a "leak / no leak" result so does not help pinpoint where the leak is in the pipes.

The boiler pressure drops by about 0.5Bar every few weeks.

Is this within the accuracy range of the gauge? And I'm assuming it's new behaviour? Could it be due to external temperature causing differences in the pressure required?

 

[Rive]

15mm copper, very basic afaics.

Very common, but not really good to have it covered... With the usual limited pipe length you get fittings (possible leak sites) everywhere

 

[sophiecentaur]

I'd like to know more about this system.

Is this within the accuracy range of the gauge?

It's always interesting to learn how different things are elsewhere. I 'assumed' that "a water based CH system" would give all the necessary information but, as with domestic electrical supply, everyone has their own mental picture.
This is what you will find in many UK houses.

Possible variations are 1. No hot tank and a direct feed of hot water from a Combi Boiler and 2. Instead of header tanks, there's a direct feed of cold water in and a pressure vessel (expansion tank)on the input of the heating water, which can be topped up when the pressure drops (my system). The pressure gauge has a range of only a couple of bars (designed for just that job).
Radiators are connected in parallel across a pair of pipes (in and out) these days but old systems used to use just one pipe with rads in series with bypass pipes for when a rad was turned off. Cheaper on copper that way.
The UK style of system is fine for moderate weather conditions. Steam would presumably deliver more heating power but would require gravity return (?) which would probably require a basement for the boiler. (That's a trope in US comedy films set in big old houses with bubbling and clanking heating systems). Heating of single floor flats is usually autonomous, with no central heating source to the whole building so that limits the range of systems, I imagine.

 

[Averagesupernova]

I have to chuckle at this thread. @sophiecentaur not because of the issue you are having. I can empathize with you concerning finding a leak like this. You mention how it is interesting to learn how things are elsewhere and I agree. What causes me a chuckle is how it is often said that the split phase electrical system in the USA is overcomplicated and confusing.
-
When I look at the diagram you posted I can't help but think that the system is overcomplicated and confusing. Two separate supply tanks in each residence? I've also never heard of a system that uses one fire to heat everything although that's not to say it doesn't exist here in the US. The way you described your own heating system with a pressure expansion tank I am somewhat familiar with. What is operating pressure of the boiler system? Do you manually turn a valve to add water? The system my grandparents had was manual. My grandparents' had a pump that ran 24-7. Incredibly quiet. You had to get right down next to it to hear if the pump was running. I'm not sure what the pressure range was. I recall that they just turned a ball valve to add water when needed. Not sure if there was a bleed valve.

 

[sophiecentaur]

I have to chuckle at this thread.

So many threads manage to point out to us the amazing range of different solutions there are around the world for doing stuff that we all need.

There is actually a regulation that the mains water supply has to be physically isolated (disconnected) from the CH system (the companies are obsessed with the risk of getting nasties into the mains water. In practice, everyone keeps the hose connected and top up with a ball valve. That means bleeding to fill up the topmost radiator. Which, of course, implies that when system cools down must be breathing in air somewhere (would a tiny bit of dissolved air account for the air in the system?)

The pumps are amazingly quiet as a rule. I did have a noisy one once, when it had been mounted at the highest point in the system (durr). It used to suck air into itself and the bubbles would churn around inside it, just a few metres above us, trying to sleep at night. There was also a terrible air lock due to a long horizontal run, also in the roof.

 

[f95toli]

We've been having a similar problem on an off for a few years. Last week it got worse and I discovered water dripping from the boiler. It turned out to be a leaking diverter valve, An heating engineer is coming to replace it later today(hopefully).
The heating engineer thinks that the leak might have been there for quite some time and could explain our previous problems as well (since it is the diverter valve it leaks much more when the heating is running, i.e. really only in the winter), even now when it is leaking a lot (I have to fill up the system twice a day) it is only a relatively slow drip which when the boiler is warm dries up quite quickly.
You don't actually need to loose very much water for the pressure to drop from our nominal 1.7 Bar to 0.8Bar (which is where it usually ends up when the boiler detects the low pressure and turns off). I guess this is one reason for why these leaks are so hard to find.

Many years ago I had a similar problem when I was living in a flat. The engineer from BG came out and injected some leak sealer into the the system which solved the problem. Have you considered trying that? You can buy it in lots of places i the UK.

 

[Baluncore]

The engineer from BG came out and injected some leak sealer into the the system which solved the problem. Have you considered trying that?

I am surprised no one has suggested adding fine-ground black pepper, paprika or curry powder to the system. They all circulate until one particle reaches and seals the leak.

 

[sophiecentaur]

The engineer from BG came out and injected some leak sealer into the the system which solved the problem.

I'm clearly not the only one.
I have read in several places that water additives are not necessarily a good solution because they can gum up places where air is present inside the 'sealed' system. There are dark tales of scary events due to unwanted blockages - but those may only be in a small minority of cases.
I remember, when cars actually needed very frequent maintenance and I DIY'd, the emergency solution to a leaky cooling system was to crack an egg into a cold engine and then run it for an hour or so. And I remember a number of things available to buy; 'BarsLeaks' iirc. I also remember having to clean out a water pump and thermostat with horrible goo in.

 

[f95toli]

I am surprised no one has suggested adding fine-ground black pepper, paprika or curry powder to the system. They all circulate until one particle reaches and seals the leak.

At least here in the UK one can buy leak sealant in just about any DIY store so I doubt many people use spices, the "proper" stuff is probably more efficient but perhaps not as nice smelling
E.g.
https://www.diy.com/departments/sentinel-leak-sealer-1l/34589_BQ.prd

 

[Steve4Physics]

The first places to carefully inspect (for any dried-out traces of leaks) are the inlets and outlets of each radiator.

If the system is a sealed one (no separate open water-tank) then there is what is called an expansion vessel inside the boiler cover. The expansion vessel holds water and slightly compressed air, separated by a flexible diaphragm; its purpose is to control the central heating water pressure, to allow for the expansion of the heated circulating water. The pressure vessel and its connections can develop leaks.

Also, there are many seals around the pipes inside the boiler.

When the boiler is hot, any small internal water leaks dry out quickly so are difficult to spot.

So, if you are able, you could let the system cool, remove the boiler’s cover to look inside - around the pressure vessel and the various seals - to see if you can spot any traces of leak(s).

 

[Hotwaterwks]

Automatic air bleeding valves on radiators also allow small amounts water vapor to leave the system. There is no evidence of a leak but pressure drops over time. Removing these automatic valves and replacing them with manual valves will often solve slow leak problems. Leak sealing compounds may cause automatic diversion valves to fail.