Any plumbers/heating engineers out there?

I’m trying to identify exactly what these are:

I have an oil-fired heating system and these are fitted just above the boiler in the garage on the main 22mm flow and return pipes. The left hand one as you look them, has developed a leak around the seal at the top and I need to replace it.

Problem is, I don’t know exactly what it is! It seems to be some form of pressure release valve but I’m not sure what it is exactly.

I have also noticed recently, that hot water has been returning to the expansion tank in the loft every so often and wonder if it could be related?

I can drain down the system and get it fixed if I know exactly what I need to replace them, problem is identifying the part!

Any help would be much appreciated!

Auto air vents


If they are leaking out the bike valve top, very normal, the ones you have vcan be turned to switch them off, just turn the black bit round if it will still move, on it you will see the marks and it will only move a bit, so the marker is against the solid circle

These have nothing to do with your feed and expansion tank getting warm, that is most likely caused by the pump, over pumping or the way its been plumbed in

Dunc, thank you. I figured they’re there to try and release air from the system but I wasn’t sure if there are different types? The left one definitely seems corroded and water is getting out between the upright section and the plate on the top of it (not venting water through the nozzle on the top).

I daren’t try any twist the top in case it comes off in my hand!

If you are going to remove them both and i would, i would just fit manual air vents instead as auto ones always go wrong after a few years.
You could get 2 x 15mm compression sockets and on one end get air vents that will fit in the socket and the other end will go on to your existing pipe work

Also the auro air vents you have, do have a check valve under them that might switch the water flow off as you unscrew vents off, but most off the time they won’t seal correctly and you will get wet, fine if you know what you are doing and quick, not so good if you dont and panic easily lol

Great, thanks Dunc. That’s much appreciated. I’m just having a look to see what I can find to replace them now I know what they are!

No problem if you need anything just ask

Superb, thanks. Really appreciate your help.

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