if i recall i think head gasket only makes it blow cold, so if its blowing hot and cold could b the heater matrix on the way out, but to check head gasket see if htere is any mayo in your water cap
First though I'd bleed the system just to eliminate the possiblity of an airlock. Then do the usual checks for blown HG...mayo under oil filler cap, shiny coolant, compression test if possible.
Heater matix is a good suggestion too...gold star to Essexlad