Before replacing, consider this!
Get a SPRAY can of "White Lithium Grease" and (with the power off) thoroughly spray into the motors moving parts (using the little red tube on the can or it will be messy). Spin the motor manualy to make sure it is freed and lubricated before turning the power back on.
This worked for me and now the unit (Glow Worm FF 70) runs quieter than it has in years. Also, there is no need to remove the motor to do this. The grease is only about £5 from B&Q so it is well worth trying, even if it only works long enough to provide temporary heat while waiting for a replacement (which might not be needed yet).
Cheers,
Malloy
February 2010