THIS WAS A VERY EASY JOB TO GAIN ACCESS TO THE PCB IT HAS 4 SCREWS SIMPLE.THE PART SITS ON THE BOTTOM OF THE BOARD ITS LIKE A MICRO SWITCH WHICH RECOGNISES WHEN THE HEATING HAS REACHED ITS TEMPERATURE TO WHICH YOU HAVE SET IT AND IT SHUTS OFF THE GAS THEN WHEN THE TEMPERATURE DROPS IT CONNECTS...
I HAVE A CELTIC 2.20FF RSC COMBI BOILER THE HEATING WORKS FINE BUT WHEN I TURN THE HOT TAP ON IT WORKS FOR A FEW SECOND BUT THEN IT JUST GOES COLD AND WHEN I CHECK THE BOILER THE PILOT LIGHT IS ON BUT ITS NOT FIRING UP