Hot water but no hot rads

[Hadrill]

My CH/WH setup is a newish Potterton Suprima, single pump and two Honeywell motorised valves. The central heating circuit is an old fashioned single 22mm pipe which has always worked satisfactorily.

Over the past two years I have been resiting and replacing both the feed pipe and rads in some rooms. This summer I finished the job, having first drained down the system. Since refilling, the hot water has been working fine, but I cannot get the rads hot. The valve motors are relatively new, and I think they are working OK. The pump, which appears to be a few years old, is also working OK. What have I done wrong? All rads and pump have been bled, and the bleed valve in the loft above the boiler has no air in it.

When I switch on the central heating, the boiler ignites, runs for about two minutes and then cuts out. When the timer switches on the boiler for the HW it works normally.

Any ideas, please?

 

[ChrisR]

Airlock. Try pump on full speed. Can be a bu****. SOmetimes putting the pump in backwards for a minute or two will shove air out.

 

[AnonymousImport]

Does the pipe get hot after the zone valve? If it does then it is an airlock. If not then you are possibly looking at the valve. If the boiler comes on then cuts out its because the boiler is up to temprature and the heat cannot escape the boiler.