Just wondered if anyone had any advice on the following. I have fitted a central heating system myself, and it is all up and running, except for the following problem. The radiator at the highest point in the system keeps filling up with air. Also the pump makes a funny noise. You can hear it running but every 30 secs or so its noise changes pitch, like it is straining. It also smells a bit plasticy (like hot plastic) when running. Also the radiator that is furthest away never gets hot. I have shut all the other radiators down in an attempt to start balancing the system and then it does get hot, but as soon as I turn any others back on, even a fraction of a turn, it losses heat. I am thinking the air problem may be the vent pipe heating up? And sucking in air ? where else can it be coming from? Is the answer an air separator?