APS Open.
- Check APS and connections.
- If APS is open, replace the switch.
- If APS is closed and connections are secure, check switch resistance. If resistance is zero, replace the switch.
- Check condensate line and termination for blockages.
- Check exhaust vent for blockages.
- Press the Power button to clear the Error Code and restart boiler.
- If the problem persists, replace the main control.
