My dads heater has packed in Ive tried the fuse thats ok so i was just wondering if there is anything else simple that could be the problem or is it get the whole heater out and replace it if so how hard are they to replace?

 

I would check to see if the motor is still working.Then i would check to see if there is power goong to the heater speed switch.

 

As above I assume you mean the actual blower motor, rather than the heater matrix, which would of course be leaking if "packed up".
I would do as above and also check the earth at the motor itself, which on these I'm sure is on the bulkhead under the wiper linkage area, do able from under the bonnet by removing the panel/seal above motor, at rear of underbonnet area.
It's not at all unusual to lose a speed from the dial as the resistor pack packs up on 1 setting, but more unusual to lose power to the switch, on the highest(fastest speed) setting it is direct and not through the resistor pack that site on top of the motor, resistor pack merely cuts the voltage down for the slower fans speeds.
Could always run a live supply direct to the motor to make sure the motor itself is ok too.
tabetha