How often should i need to top up the water pressure on a boiler?

[blackhead]

I have a Worcester combi boiler and the water pressure is dropping by one bar over 2-3 months.

Is this normal?

cheers, Larry

[Andrew Gabriel]

It's not desirable, but there are probably thousands of homes doing the same. It's worth looking around at all the visible plumbing to see if you have any wet spots, but at this time of year, it may be drying on the hot pipework before you can see any evidence.

In the summer when the heating is off, increase the cold pressure up to 2 bar (to increase the leak rate), and some hours later, go round doing the same checks, and you may find the leak then.

Also, if you are topping up regularly, you need to replenish the inhibitor, as it will be getting lost too.

The system I installed 10 years ago needs topping up by about

0.25 bar every 2 years, but I did pressure test every section during installation. Regular topping up shouldn't be necessary, although getting a system this leak free is probably rare.

[The Natural Philosopher]

can be if the water has gas in it - or gets gas in it due to lack of inhibitor or whatever in the plumbing system

[thirty-six]

No it looks like you have a leak, or it is a recent fit and the water had not been de-gassed. If the system has been in service for eight years I suspect the safety blow off valve, commonly known as the pressure relief valve is weeping. If you can identify the drain for this and check it,for moisture, that would strongly point to it (should it be wet) being the source of your depressurisation. Sometimes, just giving the valve (red knob) a quarter turn will unseat it and slam the sealing washer back down in a different location so that you can get more life from it. Ten years could possibly be the limit for this part. IIRC it costs about a tenner for a pressure relief valve and it is necessary to isolate the upper heating circuit (with a bit of luck the boiler will have been installed with boiler isolating valves as per BS and this makes such repairs easy) to prevent drain down when replacing the valve.

[Andrew Gabriel]

Don't do this unless you have already established it is weeping (e.g. using the plastic bag method mentioned by harry). Opening the valve can cause it to leak by getting debris caught on the valve seat. Then you'll have two leaks;-)

[thirty-six]

I've had that happen and kept going until the crap had been flushed out. The seeping at the pressure-relief though was probably initiated by overfilling the sytem after the expansion tank air valve seeped, so forcing the crap to the valve in the first place as the valve opened with increasing system pressure. If it leaks now, it was going to leak anyway, so better to get a known problem over with to help the diagnostic (of failure) analysis of the complete system.