The click of the thermostat is the bimetallic switch? this closes an electrical circuit and 'tells' the boiler to fire, assuming the timer isn't overiding it? Pretty sure the pilot light should be on 24/7. Essentially it's either preventing itself from firing for some pre-programmed reason, or it's knacked. Have you had a good read through the manual (maybe downloadable if necessary)?
Agree with Mr Church - check the electrics. Hell, we all know electicity is the route of most
our problems!
