....now I am desperate, I am going to try refilling as you said tonight if I can (dam no tools tools left in van!)
I'll be over the moon if it is just an airlock. It seems to behave at idle but if you drive it the temp hits 90 deg and just keeps climbing in a very short space of time
I would be inclined to remove the thermostat, refill and try the Alp without it. Also check the thermostat as described above.
Just to put all the comments together re:- filling with coolant.
Loosen both bleed valves, fill slowly, (as Dave said, 1 ltr bottle at a time) leave say 30secs or so between fills. While filling, repeatedly squeeze the rubber hoses, this will dislodge air in pipes. When coolant spills out of rad bleed valve, tighten it up. Continue until coolant comes out of thermostat bleed valve....then tighten that one up, top up to just above the plastic upright in reservoir. Once full, cap on, take the car for a spin, the action of acceleration, braking, turning left and right will help dislodge air in remaining air pockets. This will not happen if the car is stationary. Dont go too far as level should drop as air pockets fill. On return let engin cool, remove cap, bleed both valves, then top up. You may have to do this a couple of times.
Just as an aside, it does not matter if the heater is on or off, the heater matrix coolant when running is always as hot as the engin coolant, the only thing the heater on/off control does is direct air either into the car, or not. The heater matrix actually acts as an extention of the rad to aid cooling.
Hope this helps
John