I have a non pressurised central heating system. I had to change a pressure relief valve and drained the system to do it. I put everything back together and I was not happy with the upstairs rads. I must mention that i have only two rads in total upstairs.
I got lots of air from the system and ended up happy with the ground floor rads (12 in total). I listen to the circulation pump and I hear a whooshing noise every so often as it circulates the water. It must be air. However I can't get upstairs rads hot so I disconnected one of the rad feed pipes and there is no water coming out. I though that as I take the pipe off the rad the expansion tank should push water in my face as it tries to refill the rad. If I blow down the pipe i can hear water. If I take off both pipes from one rad I have no water.
I traced the feed / return pipes and only one will get hot about 6 inches on the ground floor. I don't know where they go before that as they are in the ground.
It must be an air lock as the system was ok before i changed the valve.
I have a kind of a theory!
Is it possible for the weight of air trapped in a pipe to push against the weight of water flow in an expansion tank.
Whats the knack for getting air / water out of upstairs rads?
Any help would be great.