Hi new to the group im hoping someone could help. My cars temperature seems to stay around the 85-90c mark most of the time but every so often will raise rapidly to 120c, after stopping for no more than 2 mins to allow to cool down it will return again to 85- 90c and hold there fine It seems to happen on load up hills etc. Its had the head gasket and water pump replaced last year by previous owner. cooling fan comes on and off as it should and heating is working as it should.

hows the theromostat working? using forscan you should see it climb to around 85ish then drop when the thermostat opens up and dumps all that heat in to the radiator, it will climb back up again but shouldn't go much higher, if the thermostat isnt routing the heat to the radiator then theres your problem. 

Check the hoses going to and from the rad, they should be cold then when it hits 85 they should get toasty warm. whilst you playing about with the rad, make sure its clean and not full of badgers and birds. :) 

+1 for what @Dee_82 said, it's best to start off with the basics/potentially cheap fixes.  Incidentally, @ANTONY PATTISON what engine is in your car?