Narrowboat auxiliary heater and method of controlling same

A hot water system for a narrowboat which system comprises an auxiliary heater (10) used to heat a potable water tank (30) and further to heat living areas of the narrowboat. The auxiliary heater (10) and a temperature measuring device (31) operable connected to the water tank (10) which terminates operation of the heater when the temperature reaches a predetermined and comfortable level selected by the user. Likewise, a room water circuit is operably attached to the auxiliary heater and is operated by a thermostatically controlled solenoid valve which terminates hot water flow through a radiation within the living areas when the temperature reaches a value selected by the user.