Got it booked in for Tues, next slot. Been told not to drive it though incase I cause engine damage.
If its the thermostat then it shouldn't be too expensive. A lot cheaper than a water pump would be anyway. I got my thermostat replaced under warranty last year as it was leaking.
Both thermostat and water pump seem to be common faults.
You can tell if you have air in the system as you can hear the water rushing about the passenger footwell.