I have just purchased a Disco and I noticed that when I turn the heater on it blows cold air but when I accelerate the air gets warm but not hot does anyone know what would be the first way to either eliminate some of the components that could cause this or fix it...

 

Thermostat is probably stuck open. Might need to replace it.

 

We have a 99 Disco 2 with the same issue. We replaced the thermostat and this did not remedy the issue. LR mechanic said check the heater core. Currently working on this issue with ours as well. I will post if we find a fix on our own.