My daughter's combi boiler fires up on request for hot water and central heating. The diverter valve spindle travel is good and instant. Microswitches are both activated. Flame comes on, pump is turning (removed the bleed cap and the spindle is spinning). But there is no discernible increase in the temperature of any of the pipework around the pump or heat exchanger. The outlet to the rads is lukewarm at best. The pump head was the warmest thing after switching everything off. The pump spindle spins but I don't know if it is at the normal rpm? I noticed the spindle could be pushed inward against the magnetic field a few mm, I assume that is normal. Could the problem still be with the pump and a lack of circulation? The pump is a Grundfos, and is almost silent in operation. Don't want her to buy a new pump head on my advice if it is unlikely to be faulty.