New expansion vessel fitted but......

[Dingdangdo]

Hi. BG under their homecare plan came out to fit a new expansion vessel. I can see that we are still losing pressure albiet a tiny tiny amount compared to last time. The copper pipe outside is wet....probably the odd drip every now and again. I'm beginning to think that it could be the PRV valve that might not be seated correctly hence a small leak from the copper pipe outside. Before the expansion vessel was fitted BG said it only needed a Schrader valve as it was leaking but when he fitted the new valve he bust the vessel. I go on my hols in a week so I'll call them back in a few weeks to come back and have a look. Just wanted your thoughts as we've had 2 BG engineers so far. First one bust the vessel and second one fitted the new vessel and put on a new pressure gauge. The pressure is dropping by one little line per week. Thanks in advance.

 

[Justin Passing]

Very often they do settle and stop a minor drip. So I'd leave it until you get back and see then. In the meantime you could tie a plastic bag over it to see what collects.

 

[Madrab]

They usually go hand in hand. The EV on a old system goes, the pressure rises and opens the PRV. Once the pressure problem is sorted then the PRV doesn't seat properly again and needs replaced.

Sometime it's down to crud on the seat and can be flushed past by opening the valve a couple of times. Wouldn't normally suggest opening an older PRV but if it's already passing then there's nothing lost by trying. If it stil drips then it needs replaced, that can be a real pain depening on boiler model and where the valve is situated.

 

[Dingdangdo]

It's due for a service in a month or so. I'll get my plumber to take a look when he comes to service the boiler.

 

[Mottie]

My PRV can be opened slowly by turning the red dial a little and I can see that it flows into the tundish. If I turn it quickly and further than just a little bit (about a quarter to a third of a turn) it feels like the valve opens further and at a certain point snaps shut with a 'clang'. I assume that that is to hammer the PRV seat home. Am I thinking correctly here?

 

[Dingdangdo]

They usually go hand in hand. The EV on a old system goes, the pressure rises and opens the PRV. Once the pressure problem is sorted then the PRV doesn't seat properly again and needs replaced.

Sometime it's down to crud on the seat and can be flushed past by opening the valve a couple of times. Wouldn't normally suggest opening an older PRV but if it's already passing then there's nothing lost by trying. If it stil drips then it needs replaced, that can be a real pain depening on boiler model and where the valve is situated.

I can see the valve I think from inside the boiler (saw a similar one on YouTube) . It's got a large red plastic cover on the end of it. I ain't touching it cos everything I touch with being an office dweller doesn't end well.

 

[Madrab]

My PRV can be opened slowly by turning the red dial a little and I can see that it flows into the tundish. If I turn it quickly and further than just a little bit (about a quarter to a third of a turn) it feels like the valve opens further and at a certain point snaps shut with a 'clang'. I assume that that is to hammer the PRV seat home. Am I thinking correctly here?

Yep, that's the one .... the spring is really quite strong as it's pre-loaded/calibrated so it takes just around 3bar of pressure to open it. Release the spring would always be quite strong regardless. With the twist head type of PRV the head runs around sawteeth, when twisted it lifts the spring up to open the valve, once the head gets past the top of the tooth it releases the spring, snapping it shut. I guess the tension it releases could help with seating the valve but I would reckon that's just a side effect of releasing the spring. The lever type of PRV doesn't snap like that so I wouldn't suggest that's the primary reason.