NOT up on the boiler, But would think, as it says.
Thermistor, Inlet heating, Open.
It is how you read it. The thermistor on the Heating inlet pipe is open cct.
SO find the inlet for heating, sometimes marked with an arrow, pointing in, also usually has the fill loop hose connected to it. Find the thermistor clipped onto the pipe, inside the boiler, Check with a meter if you have one, It is saying Open, so you should not get any reading, IF you do, check wiring. Repair if needed. But probably correct. Replace. Job done.
SD
December 2012