Pressure build up in radiator

Driving home one day and car started to over heat when I popped the hood it looked like coolant was boiling out so I let it cool down and put water in it to get it home was running fine before that day had to drive it about 20 min to get it home but it kept over heating so each time would pull over and add more water cause it kept boiling out. So finally got it home drove it to my work at jiffy lube and serviced the radiator with bran new coolant and new cap driving there it didn't over heat but when I popped the hood the pressure was pushing the coolant out so I have a bad fan relay but jumped it and bypassed it do fans would run when car is on and replaced head gasket and still doing the same thing just trying to figure out where to go from here will be replacing thermostat soon.