Sealed system losing pressure - how to locate leak.

[citizen]

Hi,
I have a sealed central heating system that loses pressure. I have to top up every 2 weeks. Is this excessive?
Last year I had a bad leak and the engineer put a leak sealant in the system that didn't work. I eventually found the leak and it was fixed. Now the pressure is lost much more slowly. Would it be worth putting more leak sealant in (why didn't it work last time on the smaller leaks).
There is a particular radiator that gets air in more than the others, does this indicate the leak is likely to be near this radiator?

Is there any way of locating the leak other than taking up floorboards? I have laminate flooring so taking this up would be a last resort.

Thanks in advance

 

[croydoncorgi]

Losing pressure in less than a ouple of months demands investigation - going from 1 Bar to zero on most system represents AT LEAST a couple of litres of water which have gone somewhere

On a sealed system, NO air should get into the rads. That's mostly the point of having the system! However: if you are getting air in one particular rad, then possibly you are very close to finding your leak. Think of the CH system as a closed loop with a pump at some point. When the pump's running' on the delivery side, there's higher pressure than on the inlet side.

You have a sealed system which is presumably set to 1 Bar or so at the boiler. In most cases, that 'overpressure' ensures that every part of the system is above atmospheric pressure. This is good because it means that water is pressing against O ring seals in rad valves etc. all over the system which tends to tighten them and stop them leaking.

But you also have a leak. So the pressure drops and eventually reaches the point where at some points in the system (between the 'neutral point' and the pump, in fact) the pressure will be lower than atmospheric. If the leak is in this area, it will drip when the pump is off and draw air IN when the pump runs.

So - to find your leak, start at the rad which collects most air and work BACKWARDS, against the direction of flow, along the pipework towards the boiler. Your leak SHOULD be somewhere between the aired-up rad and about halfway around the system.

Note that this approach is NOT guaranteed - the worst-affected rad may happen to be the highest one in the system - air will also collect here naturally.

Leak sealant MAY work but in my experience should be the last resort not the first.

 

[Kingsway]

Check your boiler stat isnt up way to high as this will encourage pressure drop over shorter period

See how many times you can boil a kettle before it boils dry

 

[croydoncorgi]

Check your boiler stat isnt up way to high as this will encourage pressure drop over shorter period

See how many times you can boil a kettle before it boils dry

Huh??

If your boiler's main thermostat is so wrong and your overheat stat is inoperative, you should get both fixed! Or maybe your expansion vessel is shot and / or has the wrong preload or is too small for your system. If the latter, you'll lose water out of the Emergency Discharge pipe.

Despite the name, boilers ain't supposed to boil - and generally don't. Also, with a sealed system, the overpressure of 1 Bar pushes the boiling point higher anyway. Running the boiler too hot may waste gas but the only effect on system pressure is that it will go up a bit as the boiler heats up.

None of these possibilities is anything to do with the problem originally reported in this thread.

 

[ChrisR]

Couple of the favourite places for sealed sytems to leak are the automatic air vent WHAT'S YOUR BOILER???????!!

and the rad valves.
Take the cap off your (non thermostatic) rad valves. If there's a nut around the central shaft, tighten it. This will make the valve harder to turn but that's where they tend to leak. Loosen to turn then retighten.
Leaks of hot water often just evaporate so you don't see them.

 

[citizen]

Thanks for all the replys.

CrisR,
My bolier is the British Gas ICC2 (not sure who manufactures it).

The radiator that gets air in makes a noise that the others do not, although there is no visible water leak in the garage below.
Is it possible for air to get into the system and the pressure reduces without the tell tale signs of a leak?

Thanks

 

[Passat]

Hi,

I am no plumber (at all !), but have got the same problem as yourself, but as at 2 days ago i think i may have found the problem. My leak (fingers crossed), was in two places.

1. The auto valves mentioned earlier.
2. On both joints above and below my pump, they both had small ''slits'' which my plumber told me were to turn off the flow of water to change the pump. He says these often leak over time, and they had been leaking for a while. Only time will tell if i have found them.

Good luck, but i found that depending on when you look over the pipe work is dependant on if you are lucky enough to find the leak, at times the same pipework i found the leak on was perfectly dry. I think it got worse when the system had been on and then was stopped.

 

[Jackrae]

There is a remote possibility that you don't actually have a leak.

IF your system expansion vessel has lost its pressure charge AND your system has no inhibitor fluid added what may be happening is that water is being lost to the corrosion process and the "air" you are collecting is actually a product of the process

 

[45yearsagasman]

Congrats jackrae, you have replied to a 10 yr old post. Must be a record.
Your advice however somewhat feasible.

 

[Jackrae]

Must admit I didn't read the date

 

[JohnB47]

And I've just sat and read the whole darned thing!