Sounds like the thermostat could be stuck open. Does the temperature needle sit a bit lower than usual?

Try this to confirm it:
Sit the car in your driveway and let it idle until its up to temperature. Check the temperature of the heater. Now jump on the highway/freeway/somewhere you can do 100 safely and see if the heater is a lot cooler now. You should also notice the temp gauge drops compared to when you're not moving.
If this is the case, either your thermostat is stuck open, rusted through or they took it out and forgot to replace it when they changed your radiator.

Ideal fix would be to take it back to whoever fitted the radiator and ask them why the thermostat was working before, and isn't now.

since the radiator guy is on holiday, i just wanted to know if this issue could cause any potential problems with the car if i continue to drive it?