discovery 300tdi auto 1994 heater/temp problem??

i have a 1994 discovery 300 tdi auto, yeaterday i had to replace the waterpump due the bearing going, so replace with a geniune one, today after getting up to temperature, put the heating on and was blowing cold air, then after driving a bit further the temperature guage went right to the top for about a minute, so went to pull over then all of a sudden the temp went back down to half way, and the heater was blowing hot air, its done this twice today! can anyone shed some light on this please?????

Air lock bleed it

Sounds like you didn't bleed the cooling system properly when you refilled it.

Did you do a final top-up via the thermostat housing? Did you let the engine tickover for a while, with the header tank cap off?

ok have now bled the cooling system properly and alls good now thanks for the advice (lesson learnt)