Why won't my central heating system refill?

Question

I have drained by system, and fitted a new radiator on the end of the 22mm pipes. the rad is a bathroom towel rail with non-thermostatic valves (on all the time).When I went to refill the heating system, it just would not fill, until I made one of the other rads on.

I did open the bleed valve on top of the towel rad, but it only let out a small hiss and no water. It took me hours to get water into the system. It was only when I opened the rad valve downstairs in the lounge that it all filled. Normally it always refilled straight away.

Answer 1

It sounds like your airbound system problem is all solved now.

When you say "normally it refills after you drain it" I hope you are not draining it all the time. That should be a very infrequent event since every time you drain it and add new water the new water has entrapped air that contributes to rusting inside the pipes.

Answer 2

You must ''bleed'' the air out of your system.

Bleeding air from the system
In houses with hot water heating, air gets trapped in the top of the radiators making them feel cold and reducing their ability to heat. This air must be removed or bled. On the top end of the upright type radiator there is a bleeder valve that accepts a radiator key, with a cup under the protruding nozzle open the key one or two turns. A hiss of air will be followed by a stream of water. Close the valve. Similarly behind the access cover on one end of a baseboard radiator there is a screw that operates the bleeder valve. Systems that have under floor heating use a distribution pipe with all the bleeder valves beside each other along with flow regulating valves for each circuit, these valves can be adjusted to increase or decrease the heat in each room or zone.

Answer 3

It most likely is airlocked, go to the highest radiator in the house and bleed out the air as you are trying to fill the system.