Temperature Warning Light/ Temp gauge

[DCam]

Hi everyone I'm new here. I'm a Glasgow private hire driver and drive a 66 plate 2.0 litre Skoda Octavia. 

Lately my temperature warning light has been coming on randomly. I took it to a garage and ended up

paying over £700 for 2 new water pumps, new thermostat, new sensor and new thermostat. This however

has not solved the problem. I have been assured by the garage that the car is not overheating. When the light

comes on sometimes the car loses power for an instant sometimes not. Also the temp gauge occasionally drops

to zero then back up sometimes going higher than 90. If I turn the engine off then on, it goes back to 90.

The light also comes on sometimes after just starting the car, when the engine hasn't had a chance to overheat.

I'm not sure if it is related to breaking as sometimes it comes on when I break, not always though.

I would be extremely grateful for any advice.

[PetrolDave]

When the water pumps were replaced has the system been correctly refilled to make sure there are no airlocks?

[DCam]

Yes thanks, that was something they thought might be the problem