A pilot-pressure switch operates on the same principle as the gaspressure switch used in the manifold of the gas-fired furnace or boiler. Its function is to prevent the premature failure of the spark igniter or glow coil should a prolonged gas interruption occur while the thermostat is calling for heat.
The pilot-pressure switch is installed in the pilot gas line between the pilot and pilot regulator. Installing a pilot switch requires that the pilot gas line be disconnected downstream from the pilot gas regulator. The gas line is then connected to the pilot-pressure switch by cutting the existing tubing to the regulator and connecting into the tee provided for switch mounting. A typical wiring of a pilot pressure switch is shown in Figure 5-63.