You do not say if you have what is termed a open fire in a grate or a solid fuel burner with closable door (made by parkray or rayburn) I take it you do not know if your hot water tank is direct or indirect, there fore advised to let fire burn down, then turn off water supply to feed tank and open hot taps to run off hot water in order to relieve any pressure to the boiler. the system will need further draining in order to empty complety.
B Walters
October 2007