I've never heard of a Potterton One Rad. Is it a new boiler?
M
December 2008
If the one rad that isnt working has a thermostat on it the chances are that the pin inside the valve has stuck.You need to take the t/stat top off which just unscrews and with a small set of pliers gently pull the pin up and down to release it.Eventually you should find it starts to heat up.