I have an Ideal Vogue Max system boiler with an external weather compensation sensor, and I randomly looked at the external temperature reading displayed on the boiler, and it read 31oC when the October outside temperature was considerably lower than that.
To test if the external thermistor was faulty, I removed the thermistor and connected a 18k Ohm resistor in its place and then turning the boiler off at the mains, then back on again I was looking for the reported temperature to be ~10oC.
Happily the displayed external temperature value was near enough so I ordered replacement 10k Ohm NTC B3435 thermistors from Amazon, the key parameter is that at 25oC the resistances is 10k Ohms.
The image show’s the difference in temperature reading between the original sensor on the left and displayed in blue and the new sensor on the right displayed in red which is accurate.
I’m assuming that the original thermistor suffered thermal damage as a result of being mounted on a brick wall with ambient temperatures in the height of summer of just over 41oC as measured on my weather station.
The damaged thermistor was replaced with the new one and reconnected, the boiler was then turned of and back on at the mains and the external temperature was back to reading the correct value, this was verified by my weather station reading which is within other boiler related parameters I monitor on Home Assistant.
The cost to rectify the external over temperature reading was £4.69.
