A heating apparatus comprising a heating chamber in which a heater is configured to heat a heating liquid, a heat exchanger configured to receive the heating liquid from the heating chamber and to transfer heat energy from the heating liquid to a separate heating fluid and a pressure regulator configured to control a pressure inside the heating chamber, wherein the regulator is coupled at a first side to a pressure in the heating chamber and at a second side to atmospheric pressure outside the apparatus. A method of heating is also described.