Hi Bahco, Thanks for reply.
Checked Header. Seems plenty in there. 2" above outlet. Lots of settled sludge in bottom and a bit scummy on top.
I also notched the pump down to 1 and it has improved but not cured. It kicks in every time the pump operates, whether boiler firing or not so must be a...
Recently moved house. Got conventional boiler with microbore piping to rads c/w 3 port valve + pump + header tank.
Tested system. Get loud noise of rushing water (like when running mains tap) through rads. No sign of leaks. Tried notching down pump from 3 to 2 and turned boiler down to warm...