Abstract: A method of controlling the operation of a pressurised steam boiler (50) heated by a burner (20), which includes the steps of a) monitoring the level of water in the boiler (50), b) monitoring the pressure of steam in the boiler (50), c) monitoring the firing rate of the burner (20), and d) controlling the flow rate of water into the boiler (50) having regard to the signals resulting from a) and b) and, at least for some signal conditions, also having regard to signals resulting from c). The level of water is detected by a pair of capacitance probe assemblies (58A and 58B).

Abstract: The flow rate of water into a pressurised steam boiler heated by a burner is controlled by monitoring the level of water in the boiler, monitoring the pressure of steam in the boiler and monitoring the firing rate of the boiler. The level of water in the boiler is measured by a pair of capacitance probes. By controlling the water flow with regard not only to variables relating to the boiler but also variables relating to the burner, it is possible to provide a better control of water flow. Also, by assessing variables relating both to the burner operation and the boiler operation, an assessment of the mass flow rate of steam from the boiler can be made without employing a steam flow meter.