Central heating pressure loss

[asalcedo]

The pressure in the central heating system in my home has decreased from near 2 bar to about 1 bar in the last three months.

The system is a closed circuit one with gas boiler and separate hot water tanks.

Two years ago I installed new boilers at which time we power flushed the system well with Sentinel x800 and inhibited it with plenty of Sentinel x100.

There was very little pressure loss in the first year. I did not have to add any mains fresh water.

At the beginning of this winter, the second year, I did add some water to compensate for the bleeding of some of the top floor radiators and restored the water pressure to near 2 bar.

However, now, without bleeding any radiators, I am at odds to explain this significant pressure loss, especially because there was none in the first year and the system is well inhibited, so no new corrosion is likely. Furthermore, no leaks are apparent anywhere and there is no water released at the 3bar pressure release valve.

Any ideas?

Thanks.

[newshound]

Could be that your expansion tank has lost pressure, and you are now releasing water from the relief valve. One trouble is, once these valves have lifted they often don't seat again properly, leading to slow leakage. Poly bag tied over the "overflow" pipe outside should tell you if it is leaking.

It's often tedious though not difficult to check the expansion tank pressure. You may have to partially disassemble the boiler: check the manual. Depressurise system, then check the Schraeder (car tyre) valve with a car tyre pressure gauge. If low, inflate with a bicycle pump. Job done. I'd recommend depressurising using a drain point rather than the "easy" option of lifting the relief valve.

[asalcedo]

If I understand it correctly, you are suggesting two possible causes.

1. Release valve
2. Expansion tank.

If I am correct in my interprestation. Let me make the following comments and questions:

I have two boilers next to each other in parallel. Both have a 1 meter

15mm copper pipe attached to, I believe, the release valve. There is never any stain of any type of liquid on the floor underneath those copper pipes. They both look very dry always.

Concerning the expansion tank:

I do not have, as far as I know, any expansion tank in the system, other than any, if there are, inside the boilers. The boilers are Worcester 30 CDi , do they have the expansion tank inside the boiler?

If so, would it no be better to call Worcester to check the expansion tanks for pressure loss since the boilers are still under warranty?

[Richard Russell]

Yes, the expansion vessel will be inside the boiler.

If the expansion vessel has failed, you will see a much larger than normal variation in water pressure between 'cold' and 'hot'.

I have a very similar problem to you. The pressure in our system is slowly falling, and it needs to be topped up every few weeks. I do not see an unusually large pressure variation between cold and hot, and no water emerges from the release valve (I have fitted a plastic bag over the external drain pipe).

My conclusion is that the cause is probably a leak, although there is no direct evidence. There are several places where a slow leak would go unnoticed, including a long run of pipe within (or below) the floor screed, and therefore completely inaccessible!

Richard.

[asalcedo]

All the central heating pipes originate from the boiler at ground floor level in the garage. They are in copper, and look in great condition, no more than 12 years old.

As I mentioned, the system had been working perfectly for over a year.

Most of the pipe work is above ground and any leak there would likely leave a visible mark.

There is a basement that does have some pipe runs below ground level. But why would a leak develop there? How likely is it that this cold winter made the CH pipes in a basement, in Central London, freeze and burst? The basement has been unheated for weeks, but so have been two other floors of the house.

Doesn't an inhibited CH system have a lower freezing point than plain water? (I do not have antifreeze in the system)

No freezing in the mains water pipes, that also run parallel to the CH ones in many runs, including the basement.

Could it be a case of micro perforation of old radiators? When I installed the new boilers I also installed two Magnaclean filters. Initially they used to collect mostly very fine debris. Last time I cleaned them, about four months ago (before I noticed the pressure drop), I did notice that the debris was less in quantity, but of much bigger particle size. I could describe it as small flakes of rusted material. Almost no fine debris was collected.

All the radiators are reasonably new and seem to be in good condition, as confirmed by the powerflushing at the time, by the small time it took to flash them clean. There is one radiator however, that is older, and was far dirtier. In close inspection, however, this radiator is a dry as all the others.

Is it still possible that micro perforation exists?

Would a leak sealer additive be advisable?

[asalcedo]

Well, I have a serious problem.

The pressure dropped overnight from about 1 bar to almost zero.

After refilling, the pressure has gone from about 2.3 bar to about 1.8 bar in a couple of hours.

Pressure does not increase substantially when going from cold to hot.

It looks like I have a leak.

I have again checked all radiators and all visible pipes, no leaks to be seen. No stains anywhere.

The house was built in 1927 with brick and stone walls and wooden beams. All pipes are copper with soldered unions and installed not too long ago.

Anybody have any ideas as to how to locate the leak?

I still find it quite strange because the system has worked well for many years before.

[asalcedo]

I am now expecting an engineer from Leak Detection Specialists Ltd. on Monday.

They claim a 99% success ratio in finding the leak.

Cost is £600. Similar to what other leak detection companies quoted me.

Anybody knows what I should keep in mind when the engineer comes?

Are they really that good?