Small steady from pressure release valve

[marsman802]

Hi - I have a leak in my loft from the pressure release valve. I have just had a thermaskirt radiator disconnected and this has happened since then. I have bled all my radiators (there was a lot of air released from one of them so I appear to have cleared all of that).
I just wondered if there is something I'm missing here before I give the plumber a call in case I can try anything else first?
I've attached some pictures of the valve and pressure readings on the expansion tank next to it.
Many thanks for any ideas!

 

[terryplumb]

That's an automatic air vent ,not a pressure relief valve.
Is it permanently leaking ,non stop ? If so replace it.

 

[marsman802]

Oh really? I was really off on what this was then! Its leaking steadily, not a huge amount, but it does keep going steadily enough to create that wet patch - those pictures were from Saturday night and it has continued. As I said not gushing but constantly dripping.

To install a new one any ideas how I isolate the supply pipe here? Will turning off the cold mains do it and have all the heating and hot water off etc?

 

[Madrab]

If it's pic 1 then yes it's an auto air vent - tighten down the black dust cap for now and that should stop it till it can be replaced.

CH System need depressurised and then the vent can be replaced. If it's at the top of the system then very little draining will be needed.