A portable fluid heating tool capable of heating a flow of water under mains pressure to about 107 degrees Celsius and has a connection to a water supply via a hose. Water flows through an electrical heater within the tool, then to a thermally controlled pressure regulating valve ( 80 ) and then to the outlet nozzle. This valve ( 80 ) has a moveable member such as a diaphragm ( 83 ) sealing off a pressure chamber ( 88 ). Movement of the diaphragm ( 83 ) causes a valve ( 85 ) to open or at least partly close. When closed the valve ( 85 ) impedes, or restricts the flow of water from an inlet ( 86 ) to an outlet ( 87 ) through the valve. On the other side of the diaphragm a small quantity of water is trapped within the pressure chamber ( 88 ), so that as the valve ( 80 ) heats up, pressure within the pressure chamber ( 88 ) rises as the water turns to water vapor and the air within the chamber also expands. This increase in pressure within the pressure chamber ( 88 ) causes the diaphragm ( 83 ) to move slightly outwardly causing a pintle ( 84 ) to allow the ball valve ( 85 ) to open and allow maximum flow of the heated water through the valve ( 80 ) to the nozzle of the tool.
