DIY Doctor UK DIY Forums

Hi all,
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.

on the pump there should be a bleed valve to allow air out try that
secondly turn all the valves down and leave the rads upstairs open and switch on the system this way the pump is only circulating water to the upstairs open the bleed valves on the the two rads this may help push the air out
thirdly try draining down again close all valves down,then refill,(you may use the pump to ush the water?) then go to the two rads upstairs and open one see if this fills up and bleed do it to the second one if this works then start downstairs
is there any drain off points on the upstair rads try opening them up while the system is full this may allow the air

Hi Bobplum,
Many thanks for the feedback and tips. I will try out what you describe below and let all know the outcome.

Regards

Hi All,
Carried out Bobplums instructions to the letter and I now have hot water & no air in the system. One thing I did notice is that the pipe run from the header tank that is feeding the central heating system is very long. Its about 30 feet and its only 15mm (1/2") pipe. Any great volume of air must push back on the gravity flow of water.

Bobplum - many thanks for your advice.