Heating apparatus; heating apparatus for heating liquids and gases, especially flammable and/or explosive liquids and gases; heating boilers; heating installations, vented and unvented water storage heaters; vat heaters; electrically powered water flow heaters, in line process heaters, oversink and cistern water heaters, water boilers, fan assisted heaters, convector heaters; space heaters; flameproof air heaters using liquid heated heat exchangers, including fan assisted flameproof air heaters; electrically heated radiators; liquid filled radiators; immersion heaters; heaters; heaters for mounting in ducting to heat air passing through the ducting; particularly any of the aforesaid when adapted to be used in hazardous environments and/or for use in oil and gas industry installations but none of the aforesaid including heat exchangers