A liquid heating method and apparatus including a heat device 7 having a flow passage member forming a tubular flow passage for passing a sulfuric acid solution, a heater arranged on an outside of at least one of opposing flow passage surfaces of the tubular flow passage, a liquid draining line 10, an atmosphere opening line 12, valves 11 and 13, a liquid draining mechanism for draining the sulfuric acid solution heated at least in a heat receiving area between the opposing liquid flow passage surfaces of the tubular flow passage, a flow meter 6 for measuring a flow rate of the sulfuric acid solution, and a control unit 14 responsive to the flow meter 6 for determining a defective liquid flow in the tubular flow passage and for draining the sulfuric acid solution using the liquid draining mechanism.