Glow-Worm Fuelsaver 50 br

[Will9930]

This boiler has had a new thermostat fitted and if I turn the dial much further than 2, the boiler cuts out, pump stops. After about 3 - 5 minutes, it starts up again.
If it is left on the number 2 setting, it operates correctly.
Anyone know what is wrong ?

 

[namsag]

You sure you have wired the boiler stat correctly these incororpoate the pump over run stat and pump gets its power through this stat

 

[Will9930]

I replaced the wiring connections one at a time, so they can't be in the wrong place. I have also just checked with the wiring diagram.
There is a + - adjuster on top of the thermostat. What is it for ?
There are also two small grub screws underneath which operate the microswitches, could these be set wrongly ?