ravenheat ls80t no central heating?

can you help,just recently my central heating has stopped working,i have tried all the usuall thermostat,pressure in system,and there are no fault codes,my hot water is fine.a few suggestions are diverter valve,diverter microwsitch, ch thermistor,most said it was the thermistor,and said it was the one that clipped on the pipe ,thus no draining,i went to buy one,the parts person said it was the one that screwed in to the pipe,and everybody seems to call it by a different name,can you help what is the correct name and location of the ch thermistor if this is my problem, many thanks.