ELM LeBlanc GVM boiler not retaining water pressure

23 Apr 2006
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United Kingdom
I have an ELM Leblanc combi gas boiler (approx 12 years old).

After returning from a couple of days away I noticed that the pressure gauge was at zero. I topped it up to 1.5bar and switched on the heating. The heating runs fine, but the gauge just drops back to zero after topping up.

I'm sure that there's not a leak in the pipes, I haven't been bleeding the radiators recently either.

Any ideas where the water could be going?

Thanks in advance,

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Most likely through the leaking pressure release valve to the outside of the house behind the boiler.

Just to make it more difficult, your boiler is a rather odd French model which is no longer much supported for spares in the UK.

Just to help even less the PRV is an odd design that I have only ever seen on your model.

You should have been saving up for a replacement for a few years now. There is one trick that a helpful boiler engineer might use to extend its life for a few more months but a new boiler this summer would be advisable!

Yep a flat expansion vessel has probably caused it to open the pressure relief valve, problem is these come with all the return pipework and cost about 110 quid although all you do then is unscrew the 2 grub screws and use 10 quids worth of valve. Although if you try this site they may well help you.
search leblanc then pressure relief and you may be lucky...it will show the grub screw one for the gvm 4.20 and the screw in one for the 5.20 though the last time I ordered the 5.20 they told me it was the last one and they didn't think they could source any more....but worth a try.
Thanks for the reply guys.

I'm going to phone an engineer today to have it looked at. It's the same engineer who has serviced it for the last few years so hopefully he'll know where to get some parts.

Many thanks,

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Yep, needed a new pressure release valve, Engineer managed to get one (the very last!) so problem now sorted.
Well, got up this morning and the pressure on the boiler is again down to zero :(

Story from yesterday:

Engineer arrived, no water was coming out of the outside pipe from the pressure release valve opening, pipe was bone dry (even had cobwebs on it!).

The engineer replaced two parts:

First part was (I think!) the pressure vessel (had water escaping out of the top, as opposed to air only).

Once that was replaced the pressure release valve opened and water started escaping to the outside pipe. Checked the pressure release valve and it was dead (apparently it should have a rubber washer, and there wasn't one, so it had perished!).

Pressure release valve replaced, repressurised the system and all seemed well.

I bled all of the radiators last night (2 of them contained a fair bit of air, the remaining 6 were OK) so obviously the pressure dropped. I filled the system back up to 1.5bar and went to bed. Noticed the return to zero bar this morning.

Now I need advice:

1. A lot of air will have gotten into the system during the repairs yesterday, most of which I hope I got rid off when bleeding. Will the pressure take a while to stabilise after such repairs and subsequent bleeding/re-pressurising?

2. Disregarding a leak in the piping (for now!) could their be another explanation at the boiler-end for the reducing pressure?

Thanks in advance,

To be honest, id be cutting you losses and get the thing ripped out.They are an old boiler now and not worth the cost of parts and labour to reapir.
I agree with that, in principle. However, I'd like to find out whether the problem is at the boiler-end or whether I have a leak in the piping first!
turn the isolation valve off for the boiler and leave overnight, if the pressures dropped it wil be the boiler if its stayed the same its the system.
Mark_C said:
Now that would be useful!

Where will the isolation valve be?

Inside the boiler case...leblancs leak from the auto air vent and heat exchangers to cause a pressure loss but that amount should be noticable dripping from the bottom of the case.
It was dripping from the bottom of the case initially before it was fixed yesterday!

The water was coming from a vent/valve at the top right of the boiler. The vent/valve was replaced yesterday.

Looks like I'll have to call the engineers back tomorrow then.
Is it still dripping from the bottom of the case?, I would be tempted to get the heat exchanger checked and prepare yourself for a 600.00 shock :!: , leave it all turned off for a few hours and pray a leak doesn't appear.
No, it WAS dripping from the bottom before the engineer fixed it yesterday, it's not dripping now though.

He fixed the drip and replaced the pressure relief valve but still the pressure drops to zero.

If it's gonna cost more than about £150 to fix then it's new boiler time!
HarrogateGas said:
turn the isolation valve off for the boiler and leave overnight, if the pressures dropped it wil be the boiler if its stayed the same its the system.

Would turning the boiler to hot water only have the same effect?

Or does that only disable the CH electronically?

I'm losing approx. 0.5 bar every few hours so if it is a leak in the piping it's a pretty major one, beyond the Fernox sealer point I would have thought.

Need to go into work today so can't wait around for an engineer, will be tomorrow or friday before it's checked out again.

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