Boiler pressure loss.

[Paul Drawmer]

We had a new Icos HE18 with system kit fitted 2 years ago.

The installation has had a small but persistent leak since original installation in November 2008. The leak manifests itself as a loss of pressure (there is a system kit fitted). This loss of pressure can be a drop from 1 bar to nil over 24 hours at its fastest rate, or as in the summer, may not lose pressure for weeks on end. The boiler does not get used in the summer months and there is no pressure loss unless the boiler gets hot. When the boiler works all day, as in the coldest days, the pressure loss is quicker.

I've got a solar thermal panel fitted with a twin coil DHW tank. So that's why the boiler sometimes doesn't fire up for months in the summer. (But the tank does get bloody hot, regularly over 70 top and bottom in the summer)

I'm having an ongoing problem with the installers, since as there's no evidence of leak other than loss of pressure, they are loath to start ripping stuff out on a chase for a leak.

My questions are:

As the system only loses pressure when the boiler is used - must it be something actually to do with the boiler; or could it be a central heating joint only leaking when hot? (there's no evidence anywhere of a leak).

If it's the boiler, do they have a history of internal leaks? I'm thinking that if it's a small leak in the heat exchanger, the water lost would turn to steam and just go out the flue and leave no evidence?

I want it fixed, as all the time I'm topping it up, there's more calcium deposited, and the Fernox is getting (has got) washed away.

[Gingerbread Man]

If you're loosing 1.5 bar of pressure in 24 hours, it'll be an obvious leak, not a weep.

Do you have any underfloor heating or pipes buried in the screed?

[Paul Drawmer]

Gingerbread Man said:

If you're loosing 1.5 bar of pressure in 24 hours, it'll be an obvious leak, not a weep.

Do you have any underfloor heating or pipes buried in the screed?

That's the worst rate, sometimes it's slower than that.

When the boiler was fitted, it was a total re-pipe and fit new rads and cylinder job. So, it's all new. None of the pipes are in the screed, and there's no underfloor heating.

[Brother D]

If you can't find any obvious sign of leaking its not uncommon to have a leaking rad valve with the expansion on heating allowing water to weep out, and this can evaporate leaving little or no leaks. As a test I would leave some white paper underneath each valve so any drops will show. If there is sign of a leaking valve/trv then tighten the glad screw a notch.

[eldar]

Brother D said:

If you can't find any obvious sign of leaking its not uncommon to have a leaking rad valve with the expansion on heating allowing water to weep out, and this can evaporate leaving little or no leaks. As a test I would leave some white paper underneath each valve so any drops will show. If there is sign of a leaking valve/trv then tighten the glad screw a notch.

The white paper is good, a tissue knotted just below the inlet and outlets on the rads. Could be the expansion diaphragm is leaking under pressure. Pressurise the system to the max static pressure, with the system off and see if it loses pressure. (-4 is not a good time for this)

Is there any evidence of the vent pipe operating?

[cjs]

try tying a plastic bag over the vent pipe that runs outside, this will tell you if you're losing water through the pressure release valve.

[forty-two]

I am no expert on the subject, however I found a leaking compression joint on one radiator on our system that was loosing pressure. It wasn't much of a leak but it was enough to cause the pressure to reduce over a month or so. Pinching it up cured it.

[Road2Ruin]

I have had this problem on two seperate boilers. Once it was a leaking connection to the rad the other was a hole in the heat exchanger! Both produced similar effects over a few days and were very difficult to spot. The rad one was found after I tied some kitchen towel just below each valve and left them a few days. The paper will get wet and then dry due to the heat but you can still see where it was wet. The heat exchanger was only discovered when the boiler was serviced. The engineer cleaned the internals inculding the heat exchanger (not all will do this) and spotted it. I replaced the boiler in the end as a new heat exchanger on an old vailant was silly money.

[was8v]

I had a pressure drop due to a slightly weeping CH isolation valve and a very tiny weep in an awkward place (would require redecoration to repair) on an old system.

I squirted a can of this in to the filling loop: http://www.plumbnation.co.uk/site/fernox-f4-expres...

As much as I hate bodges (this is the equivalent of radweld) it fixed the weeps and pressure loss right away.


I suspect some installers may use this stuff as a matter of course on a new system anyway and it will only fix tiny leaks.

Edited by was8v on Monday 29th November 11:31

[Paul Drawmer]

I think this has now been fixed.

The problem was that the system ONLY lost pressure when the boiler worked, and then only intermittently.

2 weeks ago an Ideal boiler specialist was sent out to replace the heat exchanger. I didn't get the chance to examine the old one when it came out, but he said it didn't look as if it had been leaking. He obviously thought the whole exercise a waste of time.

Anyway, here we are two weeks later, and following a small amount of 'post op bleeding' the system has settled down and hasn't lost any pressure for 10 days. Looks like it's fixed, and it was the heat exchanger.

Oh, and he'd flipped the cylinder 'stat up to 90 to get the system hot. I wondered why the boiler was blinking but not alight and the pump was running. Wish he'd remembered to turn it back down afterwards. Luckily I have a whole house TMV else there could have been a scalding.