Do you suffer from only two bars?
Economy down the gurgler?
Then here's the job for you.
All you need is a 5mm Allen key, various sockets and a screwdriver.
Plastics off.
Radiator off.
Remove knackered thermostat.

The longer of the two is the faulty, seized thermostat.
Flush system with distilled water.
Install new thermostat and o ring, reinstall radiator and hoses.
Add coolant. 4LTS of 50/50 premix.
Job done. Tupperware can go on tomorrow.
Almost set for the border.