There is a button battery in the digital clock that could need replacing. The clock will still display time/programmes etc but if battery is low will stop heating from firing up. Remember to turn off electric to boiler before taking out clock to open up and replace battery.
bill
March 2017
you need to start from the beginning on this one firstly you need a multimeter test if you have 240 between the brown and blue to the clock if yes then do you have power on both black wires off the clock if no then change or link out the clock if you have a room stat check for power out of the stat if all of these are o.k. then you are moving on to the thermistor but to be honest on the 102 its usually the timer