The specification discloses an improved pressure cleaning system (10) which is adapted to facilitate complete purging of air and thus priming of the system in minimal time, and which incorporates all mechanical or electrical components constructed and arranged so as to be suitable for use in hazardous areas. The cleaning system (10) includes a float entry tank (20) connected via a U-shaped conduit (38) to a pump (42) located at substantially the same level as the tank. An electrical heater tank (88) is connected to the pump (42) and is located beneath the pump. A flow sensor (28) on the inlet to the float water tank (20) and temperature sensor (132) on the heater tank (88) are provided for sensing conditions which could lead to overheating and thus premature burnout of the heating elements in the heater tank. The controls are responsive to the flow sensor (28) and temperature sensor (132).