Dead easy, drain boiler, take off front and side panels of combustion chamber, undo the 2 nuts, disconnect the thermistor and slide it out. Pop the new one back in it's place with new washers and remember to put the thermistor back in on re-connect it. (the thermistor may be on one of the pipes rather than directly into the heat exchanger, it depends on the serial number, if you have the on with the thermistor on the pipe then stick the pug in the hole in the heat exchanger, it comes in the box)
Ian, July 2009
