If you are having problems with your coolant over pressurizing, a malfunctioning Thermostat could easily be the problem, especially if the old one has furred up like the bottom of an electric kettle!
Replacement is the only real alternative. For other parts and replacement consumables, try browsing our online 'parts list' fiche for your model. This will help you to ensure your order has everything you need for the job in hand, and take best advantage of your shipping costs, avoiding have to order one small item at a later date!