No heat in cabin...Air Lock?

My 2003 is supposed to hold 10 litres of coolant. when I drain at the valve at bottom of radiator I get maybe half that. Should I expect a different result?
Still chasing No heat to cabin. There is no heat in the two inlet pipes or the return pipe,
I have replaced the dual flow valve, Aux pump thermostat and water pump.
There is an air bleed in the coolant tank…but is it possible to still have an air-lock somewhere…and if so, how can I fix it. I’ll be really happy if someone can help.

Dave

I don’t know the S-Type, but try to park in such a way that the reservoir is elevated. Turn on the heat to full. Then run the engine and keep topping up. That is assuming it has no bleed valves, etc. Or a special procedure.

David

Thanks David. I should have mentioned that mine is the 4.2 V8
Instructions are to simply remove the bleed which is on the coolant tank and then fill . replace cap and bleed screw. run with heater on and re-check/top-up.
Thanks for the tip though. I will try it ASAP.
Dave