I have a glow worm space saver 38/50 ?

my space saver 38/50 boiler refuses to fire up.pilot light working normally. thermostat in heat position, timer set as per normal still refuses to work. Have just fitted a new thermocouple to no effect. all timers thermostat and gas valve knobs in on position, plus live power to gas valve but still not working. -- could gas valve be u/s. any ideas or suggestion welcome before i commit to new boiler. many thanks.