An apparatus 10 comprises a water storage tank 14, a heater 16, a pump 38, an injector 40 that introduces a foaming agent to the water and an outlet duct 70 to convey heated water to a plurality of lances 24 through hoses 22. The heater is arranged to heat the water in at least two successive stages 66, 67, at least the second stage of the heater being activated in pulses, the frequency and/or duration of the pulses being adjustable to control the resultant temperature. Upstream of each hose is a diversion valve 85 connecting to a water return circuit 54 leading back to the water storage tank and the water return circuit includes a heat exchanger 55, 56. The apparatus may further comprise a control valve 72 that is responsive to water temperature such that only water of a sufficient temperature is supplied to the hoses
