Temperature gauge showing hot.

[MWalls96]

Hi, This is my first post but I have found a lot of your posts and threads very useful in the past. I have searched this forum for a similar question but haven't found it but apologies if it has already been asked.

I drive a 2007 1.6 16v petrol megane mk2 estate

I've recently changed my oil, spark plus, coils, front break pads and disks cabin, oil and air filters over the last weekend and I am about to flush my coolant and break lines this weekend when I was stopped by an anomaly.

Every time I start my car from cold I wait until the revs go from 1000rpm to 750rpm before I start driving. This morning I started my car from cold and the temp gauge shot right up to just above the middle and my car sounded unhappy starting and it automatically started to rev at 750rpm as if it were warm but the fan want on. I looked in my Haynes Manuel that wasn't too clear. I've unplugged the temp sensor on the side of the thermostat and the gauge stayed where it was but the fan came on suggesting it's not a dodgy temp sensor. Does anyone know or has seen something like this before? I'd really appreciate the help as I don't want to flush the system without a working temp gauge.

Thank you