Cause of error code APS/ HEX temp sw open

Either the air pressure switch contacts are open, the O-temp heat exchanger switch has opened, or the burner door temperature switch has opened.

Warning:
If the burner door temperature switch trips, the burner door and the burner door temperature switch will be extremely HOT. Allow the unit to cool before touching. Failure to follow this warning could result in severe personal injury, death, or substantial property damage.

Solution for error code APS/ HEX temp sw open

APS:
- Check the wiring connections to switch. Wires should be connected to the common and normally closed terminals.
- Air intake lengths exceed the maximum allowed lengths.
- Check for obstruction or blockage in the air intake pipes or at terminations.
- Check reference hoses connected to the air pressure switch for blockage or obstruction.
- Inspect the burner. Replace if necessary.
- Inspect the heat exchanger. Replace if necessary.
- Faulty air pressure switch. Replace switch. 

O-TEMP HEX SWITCH 
(Applies to the 286 Model Only):
- Inspect the back of the inner combustion chamber at burner level for refractory breakdown / missing. Replace heat exchanger if refractory is broken and unit has fired.
- Check continuity across two contacts. Wires should be connected at both poles of the normally closed switch.
- Faulty O-Temp HEX Switch. Replace switch. 

BURNER DOOR TEMPERATURE SWITCH 
(Applies to the 286 Model Only):
- The underlying cause of the fault must be identified and resolved by a qualified boiler service technician before resetting the burner door temperature switch.
- Check continuity across two contacts. Wires should be connected at both poles of the normally closed switch.
- Faulty burner door temperature switch. Replace burner door temperature switch.