What does air pressure switch do on combi boiler?

The air pressure switch in a boiler ensures that waste gases are being expelled, before allowing to fire up. The fan creates a draft which allows harmful gases to be released from the boiler via the flue. For your boiler to fire up, the pressure switch needs to have recognised that the fan is running first.

How does a boiler pressure switch work?

This switch triggers when the steam pressure inside the vessel reaches too high a point and triggers the burner to stop firing. If the switch did not work correctly and the burner continued firing, the pressure would build higher and higher causing the vessel to explode.

How do you diagnose a bad pressure switch?

Here are some tell-tale signs that your pressure switch is beginning to fail:

Your water pressure is at or above the cut-out pressure, yet the pump doesn’t turn off.
Your pump doesn’t turn on at the proper cut-in pressure.
You have low water pressure even though the pump is running.

How do you test a pressure switch?

Test the Switch for Resistance Disconnect the wires connected to the pressure switch by pulling the wire connectors off of the switch terminals. Set a multimeter to test for resistance (ohms). Touch each tester probe to one of the switch terminals. The tester should read 0 or close to 0 (indicating no resistance).

How does a pressure switch operate?

Pressure switches rely on water pressure to do all the work. The change in pressure that activates the switch is provided via the water from the well. The pressure moves up through the diaphragm which presses against a piston and spring, which in turn opens or closes the contacts.

How do you know if a pressure switch is bad?

Here are some tell-tale signs that your pressure switch is beginning to fail: Your water pressure is at or above the cut-out pressure, yet the pump doesn’t turn off. Your pump doesn’t turn on at the proper cut-in pressure. Your pump runs, but it cycles on and off repeatedly.