Pressure valve??

[Bagpuss12]

I clearly have a leak on my system as the boiler is losing pressure daily although not a massive amount. I've read somewhere that if water is coming out of the pipe that runs externally from the boiler then this could suggest an issue with the boiler's pressure valve. I've checked everywhere, can't find any leaks and I have knocking pipes. Could this be a pressure valve fault and how would I check?

 

[Burnerman]

The PRV is designed to lift off at 3 bar, ejecting excess water to the outside....its a reasonable idea to tie a poly bag over the outlet just to see if there's ever any water passing.
An average boiler working pressure is 1.5 bar.
It seems like the leak is elsewhere, and it could only be tiny, actually evaporating the water as it escapes so check all the radiator valves for weeping first.
John

 

[Bagpuss12]

I placed a plastic bag over the end of the pipe prior to starting this post which I've just been out to check now and there is probably about a mug full of water in the bag so it is clearly discharging something?? My pressure gauge never runs over 1.5 bar and I have to add pressure almost every 2-4 days. Whenever my boiler is off the pressure needle drops, sometimes almost to zero.

 

[45yearsagasman]

Replace, or have someone replace the prv and at the same time check the expansion vessel is functioning correctly.

 

[Bagpuss12]

Am I right in thinking that my PRV is the red knob? Mine has 3 bar written on it and an arrow telling you to turn it anti clockwise. There appears to be some play in the knob itself?

 

[Bagpuss12]

After much checking I have now found the smallest of leaks coming from the top of the towel rail (now my wife realises how important it is for me to spend quality time on the toilet). I have replaced the leak and now not losing pressure anymore. Based on that and due to my banging pipe issue and bled the system and repressurised it hoping for a cure. The banging has reduced significantly although still there but my new issue is that when the central heating is off the pressure doesn't drop back down to the 0.5 bar where it was set to? It seems to retain all its pressure so now when it fires up I have water coming out of the external overflow pipe. Why would the pressure not drop back down to 0.5 if that's where I set it??

 

[plumbplumb]

What is the pressure at on the boiler?

Cold it should be 1 - 1.5 bar when the system is hot is should be 2 bar or so.

If the pressure is continually high i.e 3 bar when hot or cold then you have a passing issue either via the filling loop or another part where the water and heating pass (cylinder on a system boiler/plate heat exchanger or main heat exchanger on a combi boiler depending on the boiler)

If the pressure only rises up to 3 when the heating is on it's likely an issue with the expansion vessel (either lost it's charge pressure/diaphragm is nackered or the pipe from the boiler to the expansion vessel is blocked)

 

[Bagpuss12]

Cold it seems to sit around 1.5 then when it fires up it pushes close to 3 before settling at just over 2. I've tried to release some pressure but it just seems to revert back to the about pressures??