hello the problem will be your flame supervision device it contpls the lighting of your oven when you first light the oven it works om a bypass rate which is your small flame fsd senses the heat from it snd lets the main valve open and the thermostat then controls the oven in your case the fsd is not doing that first check the sensor is in the flame might of got moved if it isnt thrn you need a new fsd .i get all my parts from thermagas
chorley lancs they are fantastic num is 01257 275080
william
September 2010