Something odd with my pretty new central heating setup, unless i'm missing something. Its a glow worm flexicom 30cx put in a year or two ago. The system heats up fine intitially but seems to keep going cold after a while. I have the CH set to max of 82 on the boiler. Thermostat is calling continually for heating and the receiver shows a green light. Boiler fires now and then to heat up otherwise is making whirring sound which i guess is circulation? There are only a couple of rads on two circuits and no airlocks. As i say heats up great at first but just goes cold even though everything looks like its on. Any ideas? HW works fine.