In message , GB
writes
In the area where the pump is I've now removed all the housing so I acn see
what's going on.

The pump impeller shaft is definitely turning, but I have no way of knowing
whether the impeller has come off the shaft. So, that's a possibility.


The pump is turning - you have a call for central heating

The shaft is rotating, but you seem to have no circulation

go figure

--
geoff