Sime Air Pressure Switches
Also known as a pressure differential switch, this Sime pressure switch is designed to detect if the fan is running and is connected to the Fan via heat resistant tubes directly onto the fan Venturies. This enables the boiler to detect when the fan is running because air flow from the fan closes the air pressure switch which in turn sends a signal down to the printed circuit board (PCB) confirming the fan is running. At this point gas can be sent to the burner and the ignition process can begin.
If the fan was to stop running or jam there would be a lack of air flow across the air pressure switch which would cause the air pressure switch to open. A signal would then be sent to the printed circuit board telling the Sime boiler to stop sending gas to the burner and to turn the boiler off. The air pressure switch is a fundamental safety device ensuring the safe running of the boiler.