Troubleshooting Notes
This is a pressure switch and NOT a vacuum switch. Most pellet stoves use a vacuum switch to look for negative pressure (vacuum) to close the contacts. A vacuum switch is commonly wired as a normally open (NO) circuit that closes when low pressure (event) meets a certain threshold. This is a pressure switch and it works opposite of a vacuum switch. This switch is normally closed (NC) and power flows through the circuit without a qualifying event. If the vent is clogged, the back pressure will build in the exhaust path and push the diaphragm in the switch to open the circuit (no flow of current). If you suspect that your switch is malfunctioning and you are not getting power through the switch, simply remove the hose from the switch and power should be restored. If this happens, the switch is okay but you have a clogged vent.
The problem with pressure switches in a pellet stoves that are wired NC is that if they fail, they fail in a NC position and if an event happens where the switch should be in the open position, it may not register the unsafe qualifying event and you end up smoking out your house. Because of this, it's always a good idea to test the switch once a year by capping off your vent and try to start the stove.