Possible thermostat failing?

[wwmnw]

Temp gauge on way to work today was rising to red then falling back repeatedly over the 10 mile drive, started work at 9 and finished at 5 and the car wasn't driven or started in between them times at all but when I got back in the car at 5pm and turned the ignition to the on position the temp gauge rose to just under half way! Its not possible for the water to still be hot (especially that hot) after 8 hours of being stood is it?!

Surely it cant be the head gasket there would be other signs of that too like loss of power etc wouldn't there?

Car is a 1.6 Volvo V40

[House]

Unlikely the water would stay that hot!! gauge fault? Bad earth??

[wwmnw]

Looks more likely to be thermostat but its getting worse so its going back to the garage tomorrow, just had an aux belt and clutch slave cylinder fitted :cry::cry::cry::cry::cry::cry::cry::cry::cry::cry: :cry::cry::cry::cry::cry:

[wwmnw]

Turns out its headgasket failure