MY PROTHERM 80E BOILER IS RUNNING HEATING UP MY RADIATORS AND THE BOILER GAUGE IS SHOWING ABOUT 70 DEGREES. I THEN OPEN THE HOT WATER TAP DEMANDING HOT WATER FROM THE BOILER. THE GAS BURNER GOES OUT AND ONLY IGNITES WHEN THE TEMP GAUGE ON THE BOILER DROPS DOWN TO ABOUT 16 DEGREES CENTIGRADE.