heating thermostat

If this is a wall thermostat it should be easy to replace. If it is a standard one there should only be two wires going to it. All it does is make or break a connection.
Is the boiler working now or not.
Turn off the power to the boiler and take off the cover of the thermostat. Check how many wires it has going to it go to a plumbing merchants to get a replacement.

Thanks, yeah its a wall thermostat and boiler working grand. Will check it out later, thanks for help!