Cooling fan stays on and coolant warning

[Chris74]

Hi

Radiator fan stays on and I have a coolant warning come on to say top up coolant but it's full. Am I right in thinking that a new thermostat is required and apparently sensor on coolant bottle as failed. New sensor or is sensor in the bottle(in which case just get new bottle?). Any help appreciated before I take to garage. Prefer to do myself and save dollar.

[Vauxhall Owners Club]

I would assume that the warning lamp to say the bottle is empty is in fact a high temperature warning and if the fan is staying on then it could be a coolant temperature sensor fault or even a head gasket failure