Has anyone got a Parkray or similar for central heating?

[Southsearocks]

We've moved into a house with solid fuel central heating. It has taken me ages to work out how to get the radiators to work but now it's got colder I'm having real trouble getting them to warm up! The system uses a pipe thermometer that sets off the pump when the water reaches a certain temperature. The problem is that I can't seem to get the fire hot enough to set off the pump. It goes on for a bit then goes off for ages.

It's a long shot but can anyone help (we are cold )