Temperature gauge malfunction- air lock t25

[Howardmsmith]

Hi all. Recently changed heater fan involving removing heater matrix . Put it all back , running few miles heater worked , temp gauged worked happy days. Couple of days and 50 miles later the temp gauge drops won’t register stays left out of view . Water all gone from expansion talk behind flap , water ok in main water tank with radiator cap. Heat still coming out heater . Took front radiator bleed bolt out topped up till it bled and refitted all the caps and bolt . Heater still worked but nothing registering on temp gauge still . Went for drive heater works but still no temp gauge function . All water tanks now full ( to correct level) Could this be an airlock still ?

[Smiffo]

I know it sounds too much of a coincidence, but pop the connector off the temp sensor, loop it out with a paper clip, and see if gauge works.

It should go straight to hot with flashing LED.

Then you know the wiring is good before worrying about air locks you may or may not have?
It is possible you just needed to top up coolant ( which you seem to have done ) and temp circuit has also failed.