combi boiler losing pressure

[icedup]

Hi
I've been referred here from another forum. I'm told there are 'a lot of very well qualified and helpful people' to give advice and recommendations, so I'm hoping for both.

My combi boiler has started losing pressure. A couple of days ago the pressure had dropped to 0. I filled it via the filling loop to about 1 bar, but when I got home from work yesterday the pressure had dropped to about 0.5 bar. I filled it to 1.5 bar, and this afternoon it was down to 0.9
The boiler's a Main combi 24 HE, about 18 months old, recommended pressure 0.5-1 bar.

I've checked the prv outlet pipe. It's got a small drip, about once every 35 seconds. I don't know if this is a constant drip, but would it be enough to cause so much pressure loss?

Before I call out a service engineer can anyone suggest a likely cause besides the prv? I've checked the boiler, radiators and exposed pipework and can't find any sign of leaks apart from the prv.

If the best advice is to call out the engineer, is it okay to leave it until the new year, and just keep filling up the boiler?

If it does turn out to be the prv and idea how much they cost to supply and fit?

Thanks in advance for any suggestions or recommendations

 

[simond]

It is the PRV dripping that is causing your pressure loss.

The reasons for the dripping PRV are one of these;

- overfilling of the system at some point and detritus getting under the valve's seat
- failed expansion vessel
- too many rads (water content) for the boiler's fitted expansion vessel