Leaking Worcester Bosch Boiler

[Andrew Collins]

Ever since we moved into this house 5 years ago we've had to top the central heating system up more often than I would have liked. Once a month or so.

Now it's suddenly got a lot worse, as in once per day. I've just checked the expansion vessel. Now, the system was hot, but there was plenty of pressure in it and no water. Unfortunately I don't have tyre pressure gauge, but from years of cycling I would guess it was well over 20PSI.

I've looked for a relief valve test knob but can't find any red knobs and can't find anything that I would be confident in tweaking. Odd, I can strip down and rebuild your average Ford engine without any worries. With combi boilers I start getting really nervous though.

Whilst I was fiddling about with this (a period of no more than half an hour) about 3/8 of a pint of water came out of the boiler overflow pipe (yikes!).

The boiler is a Worcester Bosch 240.

I'm guessing that it's time to try to find a professional to fix it, but is there anything else I can do before I go spending serious money?

I've got some photos of the boiler that I can put on the we if that would help.

Thanks,

Andrew

[Fentoozler]

The pressure relief valve is right at the back/bottom of a 240 (drop the control panel down to see it), and is normaly a red one with the pressure gauge directly attached (just trace the relief pipe up to find it). It sounds like it is leaking, thus dropping pressure - flushing it though may help (give it a twist, then repressurise), otherwise drain the boiler and replace (again, twist it to drain fully, no need for mains water isolation, DO NOT isolate the boiler via its own isolation valves as these WILL leak. Not expensive, part no more than £5, you can DIY.

Angus

[Andrew Collins]

Pressure valve located and duly twisted. Cheers!

I don't think it's made any difference though. I think it might be time to find a new valve.

Thanks Angus!

Andrew

[<me9]

If the pressure is rising rapidly when heating, then it is likely that the pressure vessel has lost charge. It's easy to check but the system needs to be cold and not pressurised. You will require a pressure guage (car type is adequate) and a foot pump or similar to re-charge. About 10psi (0.7bar) is normal.

[John]

Or a blockage in the connecting pipe system to expansion vessel

[Andrew Collins]

Heh... That's actually the *first* thing I did!

It does pressurize quickly, so the amount of pressure in the expansion vessel could be wrong, but there was plenty of pressure in there when I tested it. I will try to find out what the pressure should be for the boiler and make sure it is correct.

It also leaks when the pressure is well under 2 bar (the maximum it gets to), and I believe for this boiler the pressure relief valve opens (or rather should open) at around 3 bar.

I *think* it is slightly better since I tweaked the valve yesterday. I shall try it again later, but I suspect it needs replacing anyway.

Thanks,

Andrew

[Fentoozler]

Pressure raising quickly is usually one of 4 things on a WB:

1. Blockage - unusual;
2. Pump stuck - unlikely if you're getting any CH and/or HW;
3. No pressure in expansion vessel - more likely;
4. Split in water-water heat exchanger - had this on later models (CDi range), not on a 240 however.

The PRV requires replacing (again flushing it through (twist until it clicks shut again)) - you can do this as often as you like until it stops leaking or you get pissed off. Remember to recharge when necessary.

If you do need to recharge the expansion vessel, use the guide above, but remember to leave an open end when pumping it up (e.g. crank the PRV open just before it clicks shut - it should stick open).

Angus