CH Loss of Pressure

[Meatyfool]

Worcester Bosch Greenstar 24i system boiler (with system pressure dial on panel). Megaflo water tank. Boiler is 11 years old.

Twice in the past two weeks, pressure in my boiler has fallen to 0 on the attached dial. I have filled up from the loop on both occasions. In both cases, the boiler has not worked when the heating was due to come on. After filling, the boiler will heat.

This has been a known issue - we have had a very slow leak since way back (almost certainly the pre-existing CH pipes). I have topped up every now and then.

The last two times appear to be different. Firstly the speed of the drop in pressure. Further, I would previously have had to keep the filling loop open for a few seconds to top back up to 1 (cold). Still not a huge amount of water - not worried unduly about the extra oxygen or diluting the fernox.

The past two occasions, when I have topped up, the system came to pressure in under a second. Very very little water went in. What is more, when the boiler had been on for 10-20 minutes, I checked and the boiler was at 3 (just into the red) whereas it has always gone up to around 2.

I am wondering whether this is indicative of a failure with the boiler somehow (eg the dial isn't reading right!). Yes, it hasn't been serviced in a number of years, and we are going to arrange for one soon.

We have had to have a new incoming main stopcock fitted in the past year, but to be honest I would say the pressure has been set lower than higher - I may be wrong!

Any cause for concern? I also plan to put some leak sealer in the system.

Meatyfool..

[staffordian]

I'm no expert but to me, it sounds like the expansion vessel is faulty or unpressurised.

This will cause an escape of water through the (usually copper) overflow/pressure relief pipe usually found on an outside wall with a reverse turn so any escape of hot water won't scald anyone.

These often have a Schrader valve like a bike tyre valve and can be repressurised to whatever is the correct figure. But if the diaphragm has ruptured, a new vessel is needed.

It can sometimes be cheaper and easier to fit a proprietary one in the pipework rther than replacing the original which is within the boiler.

PS If it is this, leak sealer won't help, but could cure your original leak, I guess.

PPS You can detect a leak from the overflow pipe by taping a plastic bag over it for a day or two. If you get water in it, a faulty vessel is quite likely.

[Itsallaguess]

+1 for a failure of the expansion vessel.

All the symptoms suggest that this is the case.

As a temporary check, and a solution of sorts until a more robust one is found, you can part-empty a radiator whilst the system is cold, thus creating a temporary expansion vessel, and run your CH as normal, after topping up again.

Cheers,

Itsallaguess