centralheatingpressurelossworld.com - help!

The green is copper oxide (just as rust is iron oxide) which would suggest that that joint has leaked at some point.

Whether it's leaking now and / or whether it's still an issue, I couldn't say.

(also not a plumber)

I am not a plumber or heating engineer..

Might just be a case of snugging that nut up a bit tighter.

Options
- There are companies that find leaks without invasive work. Expensive I expect but might be cheaper than paying your plumber to lift every floor board and certainly less disruptive. I think you might be able to use home insurance for this.

-put some leak sealer in

- do as plumber suggests and try and track down by sight.

- look for rusty rads/damp carpets by rads

^ that doesn’t look too bad to me. IANAP.
Expansion vessel seems the first obvious culprit. Has your plumber/boiler engineer tried recharging it…worth asking him.
Assuming you open water valve to increase pressure, when the heating comes on does the pressure rise too much?

Has he suggested isolating the radiator circuit overnight to see if it looses pressure with them shut away? This is the most basic check he should be doing to prove it's either the boiler or radiators.

If not, I'd be getting a different gas plumber for a second opinion.

I had this once. It was the expansion vessel. I was able to pump it back up with a bicycle pump and it worked fine after.

What sort of boiler is it, combi? If so expansion vessel although any plumber worth their salt should have checked that first.

Loss of pressure is usually a water leak.
Less likely is the pressure release valve leaking slightly. There will be (should be) a copper pipe venting any excess pressure from the boiler. This is a safety feature, and should only open when there is a fault. An easy way to check if this is leaking is to put a bottle or other such device on the outlet outside, and check it after a day to see if there is any water in it, it should be dry.
The pressure vessel insode the boiler could, possibly, have a leak, but, unlikely, as if it has a leak, the air will disperse, and you will not be able to charge it up any more after a few days, as there will be no air in it. There have a Schraeder valve on them, see if that has any signs of leakage around it, though many of them are right at the back of the boiler, so not really accessible.
So back to the water leak in the pipework. There are some decent plumbers around who inject the pipes with a gas, then have a sniffer device to sniff out where the gas is leaking from.That narrows it down to one area, so less disruption.

Leak tester

Many things to check, pressure relief, coil in a cylinder if you have one. Look for signs of damp, try listening with a screwdriver on rads to see if you can hear any water running with the system off. If you do try and find the loudest point as a start of investigation. I’d also be tempted to isolate the boiler and conduct a pressure test.

System or combi, do you have a hot water cylinder.
Type of boiler and age would give us a clue.
If you have a leak under the floor it will be hard to track down. Got a crawl space?
Leak sealers are available, not used them. Myself so don't have any idea of how good it is.

We had the same symptoms about 18 months after a new boiler installed. No sign of a leak anywhere. Eventually we found that it was a fracture in the heat exchanger of the boiler and the water was going out of the condenser pipe which is out of sight. Worcester Bosch engineer said when he turned up- ‘No can’t be that’ 20 minutes later was fitting a new heat exchanger.

I think you’ve got your smoking gun right there.

Verdigris (copper oxide) indicates at least some water loss, but check out all the mineral deposits below.

This is inside a boiler, so chances are the water in that pipe is hot. A small leak will evaporate very quickly, hence the only small amount of verdigris but also lots of mineral deposits where water has evaporated.

Get that joint sorted and scrub the are clean before doing anything else.

I'd be leaving that nut alone. If it's not wet it's not leaking and if you try and nip it up you might disturb what's sealing it

Eventually we found that it was a fracture in the heat exchanger of the boiler and the water was going out of the condenser pipe which is out of sight.

This was the problem with ours just after Christmas.  Replacement plus a really good service,  950 quid. Boom, nearly a grand just like that.  😭

If it’s not wet it’s not leaking

not necessarily true. If it leaks when the boiler is on, and the pressure that bit higher than at rest, then it need not leak much to lose pressure over a few days and for the leaking water to evaporate leaving no trace other than corrosion.

I had a similar looking connection to my UFH mixer. System lost pressure over a couple of weeks. The boiler would send a notification via app ‘low pressure. Boiler pressure must be >1 bar to operate’ and it’d be chilly on a morning.

Eventually the flat washer in the connector failed spewing the heating water onto the cellar floor. Replaced that and no pressure loss or verdigris since.

OP, that connector might, or might not, be your problem. You may want to clean it up or replace it making sure you get a good seal between pipe, connector, and olive.

Some of the other diagnostic steps from the hive look like good ideas to try before randomly exploring the house.

Thanks All.

Boiler is a Worcester Bosch Greenstar combi, only 3 years old. Serviced every year, last one in Sept.

That pipe with the dodgy joint is on the heating circuit, it gets hot when the heating is on.

What tips for checking the expansion vessel beyond just pressure? Is there a way to check it's not all now full of air. I note that I don't really have to put much water into the system to raise the pressure, just a wee squirt.

We've had two doses of leak sealer in and that doesn't seem to have helped.

We've had similar pressure issues and eventually tracked it down (twice!) to a leaking TRV. The leak was so small that the water evaporated before making a mess but it was enough to drop the pressure over time.

@chestrockwell I got halfway round checking the TRVs last night. All look good so far. Is it obvious when there's an issue?

Roger Bisby always recommends putting something fragrant in the system. Hopefully if there is a leak it will make itself apparent.

What tips for checking the expansion vessel beyond just pressure?

IME it starts off with the boiler running at higher than usual pressure (2.5bar or more) when the heating is on, then after a day or two it triggers the pressure relief valve and the boiler shuts down until you top it up and then the whole thing repeats.

You'll have a schrader valve somewhere in the boiler, hopefully accessible. If you purge that and a load of water comes out then your expansion vessel has failed and needs replacing. If a tiny squirt of air comes out then you just need to recharge the expansion vessel. If a load comes out (like an mtb tyre's worth) then the ev was fine and your problem is elsewhere but you still need to recharge the ev.

To recharge it, shut off the supply and return to the boiler, open the drain and fully depressurise the system then pump the ev back up to just about 1 bar - more water might come out of the drain while you're doing that. Shut the drain valve, open supply and return then repressurise the boiler using the usual filling loop.

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