sounds like the flow through the system is not high enough for whatever reason, i.e. blockage, air.

what speed is the pump set to? if it's not on max, turn it up to max and see if that helps (pump will run a bit louder)

 

My outlook on central heating problems is that, if you don't have Homecare cover:

Step 1 : When it breaks give British Gas or some other homecare provider a call and cover yourself..

Step 2: Wait a couple of days, ring them, and they come out and fix it!

It works....

 

Which way speeds the pump up Nick, clockwise or anticlockwise?

This is the pump:



Speed conroller is on the other side of the unit though (from that picture!).

 

don't know, but you'll hear/feel the difference between speeds

 

there will be an arrow with the flow direction on the unit somewhere

 

Anti clockwise should turn the pump speed i think.