What is this should it be tight? Stored hot water

[Speedy471]

Lost water pressure to the boiler. When topping up the water the pressure dropped very quickly - within about 30 seconds. I checked for visible leaks at boiler and rads - none.

Had a closer inspection and saw slight leak around the screw cap in pictures. The screw cap was quite loose. I have tightened and topped up again and pressure seems to be holding and I now have hot water. What is this cap? Should it be tight? It has never been an issue before and I have never touched this. I have filled to 1 bar however now there seems to be more air in the system compared to normal. What is the best way to remove this?

 

[CBW]

It’s a manual air vent for expelling air from heating systems, if the leak has stopped then it’s ok, use it if you need to remove any other air, just remember to close it off again.

 

[Speedy471]

It’s a manual air vent for expelling air from heating systems, if the leak has stopped then it’s ok, use it if you need to remove any other air, just remember to close it off again.

Thanks, I have had the hot water on for 20 minutes now and the pressure has maintained 1 bar. I have just put on the heating as well to test. Really odd that this would be so loose when the vent is positioned out of the way. I guess pressurised systems may loosen thumb tight screws over time. Air in the system appears to have reduced now there has been some circulation. Phew, thankfully looks like that saved me a £100 call out!