CH cuts out after 3-5 mins

[DingDongBell]

Hi all.
Hope someone can help. Central heating wouldn't work so drained system. Went to header tank to put inhibitor in and found tank still full. Found blockage between header tank and pump. Cleared blockage but now system fills up but boiler cuts off after 3 to 5 mins so rads dont get hot. Drained system again but left CH on by mistake and found boiler ran continuosly but stops when i stop the water draining. Boiler is a Halstead best 80 if thats of any relevance. I hope someone can advise. Thanks

 

[dal5band]

You'll ruin your boiler for good if you run it without water in it so make sure there is water in the system when switching on the boiler.

Sounds to me as though you still have a circulation problem - boiler heats up the water in it and the boiler will then cut-out unless water is circulating through. There may just be an air-lock or another blockage similar to the one you cleared. Start by making sure system is full and not air locked - turn pump on to max speed.

 

[DingDongBell]

Thanks for reply but i have bled all rads and pump is on high setting. If there is crap in system will it need a power flush?