Micron 60FF snag (Glow Worm)?

Hi all.
Micron 60FF playing up. Boiler works fine but ignores the thermostats and runs almost continuously until radiators are red hot. Have to control heat by turning off mains to the programmer / timer. Thought it was the frost stat, but had that checked and replaced by an electrician, along with the room thermostat, but looks like they weren't the issue.
Saw on another forum that someone with the same prob required a "resistor" from Glow Worm which he placed in between the live switch and neutral terminals, which seemed a cure. Spoke to glow Worm who stated that they had no separate part no. for the resistor and so a whole new PCB would be the answer.
Has anyone else had this problem, and do you know of a fix, or if the "resistor" can be purchased without the expensive PCB?
Thanks for any light you can shed on this