Combi boiler losing pressure

[Gazmcc84]

Hi

I have a Worcester 25si boiler, after changing a rad yesterday and filling I noticed the pressure whilst the heating was on had risen to nearly 4 bar on the gauge, down to me over filling when cold, I opened the pressure release valve to release pressure and it dropped down to zero, now when trying to refill I fill up until 1.25 bar I constantly dropped back to 0, I have bled all of the rads and checked outside and noticed that water was. Coming from the pressure release pipe outside, the amount of water slows when the pressure drops back to zeroand increases if I fill via the water inlet.

What do people think, is this pointing towards a faulty prv or could it be the expansion vessel?

Would the vessel cause water to leave via the prv or does anyone think that now I have opened the prv it is faulty and won't close again.

I guess the boiler is around 16 years old based on when the extension was built where it is situated

Thanks

 

[ianmcd]

you shouldnt use a PRV to drain a boiler , you might get away with stripping it and cleaning it but sounds like you dont really know what you are doing so will be better to get an engineer in to replace the PRV

 

[Gazmcc84]

I wasn't actually intending to drain the boiler, like I said the pressure was almost 4bar which I'm sure you will agree is quite high. After looking at other threads for advice on here I went with releasing pressure via the prv rather than via bleed valves as I thought it would be quicker and safer considering it was full of hot water at the time.

Is this likely to be the prv rather than the expansion vessel, again is it possible for a problem with the expansion vessel combined with low pressure on the gauge causing the water to leak via the prv?

 

[dilalio]

As Ian above... By operating the PRV it is likely that debris from the system whilst draining is now preventing the PRV from reseating itself and is letting by.

You "might" get away with manipulating it whilst filling the system with filling loop open, in the hope it will reseat. Else it's a new PRV.

 

[Gazmcc84]

Ok thanks .I'll give that a go the in order to try and clean it.

If not I'll sort the prv with a new one. I think they are only around £15 quid and I should be able to do that myself without getting a plumber out

 

[Madrab]

If your system is reaching 4 bar without the PRV releasing the pressure automatically - it should start to open at 3 bar - then it needs replaced as a matter or urgency, it's your primary wet system's safety control.

 

[Gazmcc84]

Update

IV tried flushing through the system and whilst increasing the pressure could hear a hissing from the top of the boiler, I located the screw cap on what turns out to be the auto air vent and tightened it and now the pressure holds.

Reading other forums give conflicting advice regarding this cap, should it be tight or loose? What could be the likely issue that's causing the air to vent out?

 

[terryplumb]

The cap has to be loose ,it will not work if its closed tight ,the air couldnt get out. Over time ,in any central heating system , its quite normal for small amounts of " air" to need to be vented.

 

[Gazmcc84]

Loosened the cap back off, the air vented out and stopped, pressure now holding better, checked and bled all rads again, pressure is dropping slightly but have noticed that there is a constant drip outside from the prv, looks like it could be the prv in need of replacement after all which was being made to seem worse by the air in the system

 

[terryplumb]

Your prv shouldnt let water out unless the pressure gets upto around 3 bar. And as Madrab advised earlier it should not allow your pressure to get to 4 bar. It needs replacing ,sooner rather than later.

 

[Gazmcc84]

Further update

Pressure held overnight, I put heating on this morning and after it had warmed up checked the pressure which got to 3 bar from 1.3 bar prv worked as it should and pressure dropped back down.
I think I am right in thinking this pointed towards an issue with the expansion vessel.
So I located and pressed the valve on the top no air came out but a very small drip of water seeped out, am I correct in thinking that this is a failed expansion vessel which will need replacing?

 

[dilalio]

Drain system again. Not using PRV. And pump air side of EV up to prescribed pressure (approx.0.8-1.0 bar depending on its size and system). But do this when water side of EV is unpressurised and able to push water out.

 

[Gazmcc84]

Drain system again. Not using PRV. And pump air side of EV up to prescribed pressure (approx.0.8-1.0 bar depending on its size and system). But do this when water side of EV is unpressurised and able to push water out.

Ok thanks I will give this a try, regarding the ev, my boiler is a Worcester 25si with an 8 liter ev inside, I have 12 rads including a couple of very small radiators and a large towel rail, is it possible the ev on my system is already too small

 

[terryplumb]

You mentioned the boiler is 16 years old ,so if its been working fine ,with the existing ev then you shouldnt worry about its size , unless you have added radiators in terms of numbers or increased sizes.

 

[Gazmcc84]

You mentioned the boiler is 16 years old ,so if its been working fine ,with the existing ev then you shouldnt worry about its size , unless you have added radiators in terms of numbers or increased sizes.

Since we moved in we have converted the garage and added 2 rads in there, this was done by a builder who used a heating engineer to add the rads, I imagine they would have mentioned something had it have been an issue adding the two rads to the boiler