Leaking valve in boiler circuit to pressurised cylinder

[nekomatic]

My CH and hot water are out of action because of a leak from the block valve next to the tundish in the picture - pressure on the gauge on the boiler had dropped to zero and when I tried to refill it it just sprays out from the stem of this valve. You can see rust marks suggesting to me that the valve has corroded - if it's original to the system it's about twelve years old.

It's a Vaillant system boiler and pressurised cylinder and the valve is on a tee off the feed from boiler to cylinder coil.

Replacing this valve looks straightforward, but two questions:

- am I allowed to touch this, given it's a pressurised system? Does it make a difference that it's on the boiler circuit not the cylinder itself?

- if so, is there anything I need to know about re-pressurising the system afterwards?

Thanks for any advice!

 

[CBW]

That valve should never have been put there and imo serves no purpose. Yes you can replace it, but I’d just replace it with some copper and coupling. Pressurised makes no difference, but you can’t work on the safety of the cylinder (G3), but you’re not touching that side?

 

[nekomatic]

Thanks. The thing above the block valve looks like a bleed valve, is that to bleed air out of the boiler circuit? I guess the block valve was there in case the bleed valve started leaking

 

[CBW]

Yes it’s a manual air vent for the circuit, connected to the boiler/heating.