Faulty relief valve or expansion vessel

[BigBird]

I am thinking one (hopefully not both) of the above is the cause of my problems. Symptoms being a fairly constant drip from the discharge pipe out doors and steady drop in pressure in the system.

The boiler is an old Ferroli 77FF IIRC.

I am short on free time but need to get this sorted as am moving house.

I am hoping to confirm diagnosis. Gauge how much it will cost to have an engineer fix this. Gauge whether it is a possible DIY job. I am competent (IMHO) with general copperwork plumbing and as a general DIYist.

I will take a closer look at the valve shortly and am giving over tomorrow to get this fixed if possible and necessary whether calling engineers or DIY.

Comments please.

[BigBird]

Well thinking about it obviously the valve must be faulty to release water at such low pressures. Anyway as can be expected testing the valve has exacerbated the fault. Now more than a steady drip.

I have a spare on standby now and inhibitor too. It is just a matter of whether there is something which prevents it being a DIY job and whether the expansion chamber is also faulty. I'm still thinking it possible a faulty chamber may have came before a faulty valve.

[Christian McArdle]

Yes, it's all possible. When you've got the system drained down, check the precharge on the expansion vessel (usually 0.75 bar). If you can't pressurise it, or water leaks out of the air hole, then it is shot.

Christian.

[Paul Barker]

You're thinking on the right lines.

Sometimes you can clear the seat of the prv by geting th ehatin roasting hot switching off the boiler and manually blowing a good je out of the prv. If this fails you do have to change it.

As a secondary issue check the expansion vessel. If it is workin correctly the pressure in the system should rise about 1/2 a bar fro cold to hot, this depends on the size of your system. If it only rise to around 1/2 a bar greater, then no need to investigate further.

If it is faulty, let all the air out (if there is any) of the Shriede valve (bike pump valve). If water comes out you need a new vessel. I air or no air but no water either, drain your system until there is 1/ a bar showing on your built in guage. Get your bike pump and manuall pump up the vessel a further 1/2 to 1 bar i.e. watch the guage go up b that amount. (whatever pressure your manufacturers instructions advise

0.75 bar if no advice.)

-- Paul Barker

[Ed Sirett]

See below.

[BigBird]

Thanks to all who replied.

The importance of RTFM has once again been proven, if only I had the manual. I do actually have pdf of very similar model now I know what I'm looking at.

Long story short I replaced the PRV without a problem. At £15 this wasn't a problem. I have also recharged the expansion chamber following the instructions/advice in the FAQ and above. There was next to no pressure in there. Whether it is damaged internally I have yet to find out.

Unfortunately the new PRV seems no better than the old. On first use it let water through at just over 2Bar. Later I noticed it letting water through at just over 1Bar. How do these actually work. Could I have damaged it already and how. Any liquid I have collected from the discharge has not contained any obvious contaminants.

I could understand the one I removed failing. There was a certain amount of sludge like material at the entrance to the valve.

I shall see if a couple of test discharges at full working temp help else I guess I need to see if I can get hold of another one...

...got called away time passed and I have actually tried this a little earlier now. Problem with PRV seems to have gone away.

Shall see how things go. Cheers.