Mystery Leak in Central Heating

I've had a brand new boiler installed recently as the previous one was knackered anyway but we also thought it was leaking out of an outlet pipe. We had to top up the water pressure every couple of weeks.

I've just had to do the same with this new boiler which makes me think that there is a problem somewhere else in the system.

I've no idea where the leak could be as there are no traces of moisture on the floors, ceilings or around the radiators since we've been in the house (around a year). I would've thought that if there was a leak in the central heating system then it would empty far more rapidly than over the course of a couple of weeks.

My questions are, how do I find the leak and is there something about central heating systems that I don't know and should be investigating? Thanks.
 
Actually my missus is going through this exact thing, she said when home serve came around they found the outlet pipe slightly out of position, that solved the condensation problem, but still got to add pressure into the tank every few days
 
I had a similar issue with my old boiler which continued after having a new boiler fitted.

The problem was a very small weep at the nut securing the feed pipe to the radiator valve in one of the bedrooms. The water that leaked out either evaporated before it had a chance to mark the ceiling of the room below or it was absorbed by the carpet and the chipboard flooring.

I had checked all the valves when the the system was cold, but I discovered the leak when it was on and circulating hot water through the pipework. Once I had finally discovered the problem, a replacement valve sorted the leak, but I was faced with replacing a section of floor and the carpet.

If I had a re-occurence of pressure loss, the first thing I would check would be the carpets and floor below each radiator.
 

Joshua Slocum

LE
Book Reviewer
put talcum powder down under the valves at both ends of the radiators
It may be that the plumber did not fully vent the system and trapped air has come through
go round and vent all the rads and run your hand along the bottom edge looking for leaks
top up the system and keep a note of when you did it and see how long it takes to drop
also make sure all the bleed valves are tight
you may well have a leaking TRV
a good plumber should have pressure tested the system first
 
For a boiler to run out of water means some pretty significant leaks doesn't it? There should be a pool of water somewhere...
 
Did you have the system flushed when they installed the new boiler.....yes, yes, I know they are supposed to do it, but the twats sometimes never bother. A good proper flush takes around a couple of hours to half a day.

1. How old are the radiators? The black stuff in the water that comes out of the rad's is basically rust solution, the rads slowly rust internally from the day they are made in the factory. Nowadays with the thin pressed sheet steel rads it can get to the stage where the metal is so rusted through that it is just the paint on the outside holding them together. Meanwhile the micro holes in the rad's effectively let out micro particles of water......a bit like goretex, sucha a small amount at any time you would not notice it. Go around and tap the bottoms of the rads with a screwdriver handle, or similar make sure they make a nice metallic noise.

2. Check the valves on the rads they may be leaking tiny amounts of water. Use very dry fingers, or kleenex tissues to feel/spot water.

3. Have a look at the bleed nipples see if they are leaking.

4. Go up the loft when the heating has run for a while and is still running see if there is water coming up out of the open vent pipe into the feed and expansion cistern - thats the small cistern in the loft. If that is happening it may be that the hot water coming into the cistern is condensing away enough over a couple of weeks for you to need to top up.

5. Run a dry hand/tissue over every pipe you can at the joint areas. You may have a micro leak from a badly soldered joint. A micro leak would be so slow it would not be visually noticeable. Imagine a leak coming out between a joint and then running along a downward slanting pipe for a couple or three feet and it would have almost evaporated before there is a drip. You can get moisture detectors a bit like those point and shoot laser thermometers only they detect moisture - even with a micro leak there will probably be a moisture build up.

I did one as a favour for a mate back in UK before I came over, same thing leaky heating and having to top up. Traced all the pipes round the house with a metal detector drilling holes to stick my fibre optic camera under the flooboards to have a look every couple of feet, eventually found the leak. The builder had run the circuit under the screed floor from one side of the living room to the other and there was a micro leak in a soldered joint. Took out a square foot of floor 4 inches deep after lifting the carpet, underlay and tiles, fixed it and he sorted the floor.

I feel for you as there is no really easy way.

BTW you lot, use the correct terminology:

Tank:



Cistern:


Cylinder:



This is an unvented cylinder:

 
Last edited:

Slime

LE
if you are only topping up the system every couple of weeks you aren't looking for a leak big enough to make anywhere wet or damp.

Start with the areas you can see such as radiators, radiator valves and any exposed pipework.
As you are topping up the system every few weeks it sounds as though your filling loop is permentantly attached, check that too. If you use a stop rap style tap to top up the system check the area around the base of the crutch head stem, if you use an isolation valve where you open it with a screwdriver check all around the round knob you insert the screwdriver into.

Dry everything off, then check each and every fitting by curling your index finger around joints and couplings etc.
You can't accurately tell by feel if a fitting has a slight leak so the trick is to look at the inside of your index finger before testing each joint to ensure your finger is dry. Then look at it after testing, a tiny leak will leave a slight glisten on your finger that you need to see as you provably wouldn't feel it.
Checking each and every time also stops you missing which fitting was actually wet.
 
For a boiler to run out of water means some pretty significant leaks doesn't it? There should be a pool of water somewhere...
A micro leak may run along a hot pipe and more or less evaporate before it has chance to drip. You would only see the run marks on the pipe if you lifted floorboards.
 

Slime

LE
For a boiler to run out of water means some pretty significant leaks doesn't it? There should be a pool of water somewhere...
No, a significant leak would take the boiler pressure down in seconds, just think how quick the pressure gauge rises when you top up the water via the filling loop, it may well go from 0.2 bar to 1.8 bar in two or three seconds.
 

Joshua Slocum

LE
Book Reviewer
For a boiler to run out of water means some pretty significant leaks doesn't it? There should be a pool of water somewhere...
there is a difference between running out and losing pressure, its a sealed system if you get too much air in it the temperature can rise and the pressure increase and bump out the safety valve
are their any signs of leaks around the base of the boiler, thats why I said vent each rad and then re pressure the system, make sure the system is cold and not running either, or you get trapped air
once you have done that keep an eye on the pressure gauge, maybe take a photo every day, if it drops again call the plumber
if you have any pipes running under floors, pop a board up and have a sniff for damp, or roll some tissue on a stick and rub it along the bottom of the pipe then look for moisture
 

Slime

LE
Did you have the system flushed when they installed the new boiler.....yes, yes, I know they are supposed to do it, but the twats sometimes never bother. A good proper flush takes around a couple of hours to half a day.

1. How old are the radiators? The black stuff in the water that comes out of the rad's is basically rust solution, the rads slowly rust internally from the day they are made in the factory. Nowadays with the thin pressed sheet steel rads it can get to the stage where the metal is so rusted through that it is just the paint on the outside holding them together. Meanwhile the micro holes in the rad's effectively let out micro particles of water......a bit like goretex, sucha a small amount at any time you would not notice it. Go around and tap the bottoms of the rads with a screwdriver handle, or similar make sure they make a nice metallic noise.

2. Check the valves on the rads they may be leaking tiny amounts of water. Use very dry fingers, or kleenex tissues to feel/spot water.

3. Have a look at the bleed nipples see if they are leaking.

4. Go up the loft when the heating has run for a while and is still running see if there is water coming up out of the open vent pipe into the feed and expansion cistern - thats the small cistern in the loft. If that is happening it may be that the hot water coming into the cistern is condensing away enough over a couple of weeks for you to need to top up.

5. Run a dry hand/tissue over every pipe you can at the joint areas. You may have a micro leak from a badly soldered joint. A micro leak would be so slow it would not be visually noticeable. Imagine a leak coming out between a joint and then running along a downward slanting pipe for a couple or three feet and it would have almost evaporated before there is a drip. You can get moisture detectors a bit like those point and shoot laser thermometers only they detect moisture - even with a micro leak there will probably be a moisture build up.

I did one as a favour for a mate back in UK before I came over, same thing leaky heating and having to top up. Traced all the pipes round the house with a metal detector drilling holes to stick my fibre optic camera under the flooboards to have a look every couple of feet, eventually found the leak. The builder had run the circuit under the screed floor from one side of the living room to the other and there was a micro leak in a soldered joint. Took out a square foot of floor 4 inches deep after lifting the carpet, underlay and tiles, fixed it and he sorted the floor.

I feel for you as there is no really easy way.

BTW you lot, use the correct terminology:

Tank:



Cistern:


Cylinder:



This is an unvented cylinder:

It's a pressurised system so won't have an F and E tank in a loft............can't really pressurise open systems too well ;)
 
It's a pressurised system so won't have an F and E tank in a loft............can't really pressurise open systems too well ;)
Did he mention that............must have missed it. Cheers.:)
 

Slime

LE

Slime

LE
Something Joshua said may be worth a closer look.
As you only said you had a new boiler you may may still have your old rads and thus old rad thermostatic valves.

If that's the case and you have thermostatic valves with round heads that you turn to alter the temp of a radiator you could have. Leak inside the part you turn.
They have a little pin inside that rises or lowers due to expansion of wax within the valve. On older valves the pin can develop a leak around its seat. If that is leaking the water will not show or will evaporate before leaving the head of the valve.
To remove the part you turn there is normally a chrome or silver coloured collar just below the part you turn. Unscrew that anti clockwise fully and then the head will pull off with a click. The inlet valve at the other end of the radiator normally just has a pushfit cap. If those ones are a bit tight it's best to push them upwards from the bottom as they become brittle with age.
 

Slime

LE
A picture is worth a thousand words etc :)

 

4(T)

LE
I had a similar issue with my old boiler which continued after having a new boiler fitted.

The problem was a very small weep at the nut securing the feed pipe to the radiator valve in one of the bedrooms. The water that leaked out either evaporated before it had a chance to mark the ceiling of the room below or it was absorbed by the carpet and the chipboard flooring.

I had checked all the valves when the the system was cold, but I discovered the leak when it was on and circulating hot water through the pipework. Once I had finally discovered the problem, a replacement valve sorted the leak, but I was faced with replacing a section of floor and the carpet.

If I had a re-occurence of pressure loss, the first thing I would check would be the carpets and floor below each radiator.

Ditto.


I have to top up the pressure in our boiler very ten days or so when the heating is on.

The only leak in the system is a tiny intermittent drip from one of the rad valves. Its only really detectable if you leave a tissue under the valve and, although its evidently been like that for a couple of years, the drip has yet to penetrate the carpet and stain the floor underneath - it evaporates before doing so.

Its microbore and the valve nut is already pinched up as tight as is as is sensible.
 

Joshua Slocum

LE
Book Reviewer
Ditto.


I have to top up the pressure in our boiler very ten days or so when the heating is on.

The only leak in the system is a tiny intermittent drip from one of the rad valves. Its only really detectable if you leave a tissue under the valve and, although its evidently been like that for a couple of years, the drip has yet to penetrate the carpet and stain the floor underneath - it evaporates before doing so.

Its microbore and the valve nut is already pinched up as tight as is as is sensible.
Microbore is a real PIA, the pipes become brittle with age and can often get small hairline fractures where the olive sits, also some plumbers do not take the trouble to ensure that the pipe meets the valve parallel , and the cockeyed seating can leak, i cut ours back after draining it, soldered a new section in and terminated it properly, no more problems
 
All this is causing micro leaks in my mind.

The radiators are old so replacing them might be a sensible move.
 

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