Hi, I hope someone can help me diagnose this problem. Yesterday
overnight a leak occured in my central heating circuit. I drained down
the system and repaired the leak, then refilled and bled everything I
could find several times with the CH off - radiators, pump and a vent
screw

Now when I switch the boiler on it fires up for between 30s and 60s
before shutting off. It is an Ideal Std gas fired boiler (non-combi).
During the brief period when the boiler is fired, i have discovered
that the flow return pipe is cold and the pumped flow pipe gets
scalding. The pump is definitely running upstairs but I'm wondering if
there's either a large airlock or whether the pump is damaged and not
shifting water - resulting in the boiler heating static water and then
shutting down as it goes over-temperature.

Can anyone suggest how i check this or give me an idea what else it
could be? Could the pump be operational (it's quiet) but damaged enough
not to pump water? Any ideas for purging any remaining airlocks out of
the system.

It's either that or shelling out for a new CH pump to discover if
that's the problem (

Thanks for any advice you can give.