Bulldog TRV stuck

C.C.L.

Hi all, on the radiator in a spare bedroom, the radiator is very hot and it won't turn down with the TRV. Husband has taken the cap off, tapped it and tried to get the spindle (is it a thermostat?) thing to move but it won't budge. We've had it on 0 and the snowflake setting but it's still hot.
Anything else we can try? I did wonder if we can get a new spindle thing for it, but how would we fit it? Or is it a whole new TRV that's needed?
Hopeless at anything D.I.Y so any idiot proof replies would be great! TIA.

sk240

They are cheap enough
http://www.ebay.co.uk/itm/Pegler-Bulldog-15mm-Angled-TRV-Thermostatic-Radiator-Valve-Lockshield-Pack-x1-/180695004907?hash=item2a1242f6eb:g:EzYAAOSwdsFUOA~3