peugeot partner 2.0hdi running hot

[VANRENTAL]

I have a 2005 partner van and after about 10-15mins of normal driving the temperature guage creeps up to about 100-110.
Normally it should run at about 90 degrees the engine does not boil up or use any water and the fan kicks in and out at about 100 degrees
I have changed the thermostat this made no difference, if i put the heater on full blast and drive with less revs it does run a bit cooler.
Has anyone had this problem could it be water pump or head gasket etc?? I have checked temp on engine with infared temp tester and the guage is reading correct