Fernox F4 leak sealer - or alternatives

Chris B pretended :

Have you tried fastening a sandwich bag over the outlet from the pressure release valve outlet, with an elastic band?

Well that is a bit tricky as there are three pressure relief devices (boiler pressure, tank pressure and tank overheat) all feeding into the same tundish. I have put my finger there and it seems dry but I suppose I could put some kitchen towel in the tundish (making sure it cant go down the pipe).

My system pipework is pretty old and it was also losing pressure. For some reason I was sure it had to be the pipework.

When I belatedly did stick a bottle on the overflow, sure enough, it was being expelled there. Repressurising the tank sorted the ?leak? instantly.

Tim

Tim+ wrote on 08/04/2022 :

You mean the re-pressurising the 'expansion vessel'?

Indeed. Dunno where ?tank? came from. I blame autocorrect. ;-)

Tim

Where would one normally find that valve, please?

Depends on your system. If the pressure vessel is inside the casing of the boiler one of the pipes coming out will be from the PRV. The valve should be accessible inside the casing but not necessarily obviously! It can be well tucked up inside the casing.

The outlet is *usually* taken straight outside through the wall but it can also be merged with the condensate drain. If it goes out through the wall it usually has two right-angle bends in it to direct any blow-off back towards the wall.

Tim

Brian used his keyboard to write :

You don't need to find the valve, you need to find the outlet pipe. Normally that will be poking out through a wall, to the outside. The pipe will poke through the wall, have elbows in it, so any got water squirts out at the face of the wall, where it cannot injure anyone. Just pop a sandwich bag over it and see if any water collects any water.

But in your case the hot pressure would rise considerably. The Op's only went up slightly when the system was hot and the pump was running.

I use a hand pump to repressurise my system. If it rises with few strokes of the pump I suspect teh pressure vessel, if it is more then it is a leak, which is in my case either crud on teh spindles of the TRVs, or the bleed valve on the heat exchanger leaking.

But did the OP watch it continuously? I never saw my system over-pressure despite my gauge being relatively accessible in my garage.

I guess that with hindsight, just watching the gauge whilst repressurising (from depressurised) should have given me a clue. The pressure would come up very quickly.

When I did eventually apply an air pump to the pressure vessel, the air pressure shot up to 200psi and stopped! Turned out the diaphragm was stuck to the back of the valve.

Tim

Once I realised there was a problem (ie after the second or third top up is as many months) yes I did. From freshly topped up fully cold radiator system to a fully hot radiator system. Stating at 1.5 Bar it never went over 2 (Max was ~1.8)

In my case I fill up from a filling loop whilst watching the gauge. I only "crack open" the filling valve but it takes 3 or 4 minutes to go slowly up from nominally zero to 1.5 bar (cold)

Hmm. On my boiler, installed by professional plumbers, the overpressure relief has been linked to the condensate drain and then taken directly to an internal soil pipe upstand!

Thank you.