Red coolant warning

[griswold]

This red coolant warning keeps popping up at random times. Took the car out for a run to Brecon then back through Monmouth no problems while driving till I parked outside my house. I had the climate control displaying 88,89,87 deg. most of the time while driving. Checked when parked outside house was showing 90 on climate may have dropped from 91 does the warning come on after 90deg? oil temp fine gauge for water sits at 90 all the time. Ordered a new CTS anything else I should look at? I recently changed my coolant tank could the level sensor on that show that red error? Might put original coolant tank back on and try that?

 

[aragorn]

Yeh the level sensor will bring on the light.