4+3 Low/medium pressure switch open while medium/high switch closed

What the control is telling you

Pressure switch states do not make sense: a lower switch is open while a higher one is closed.

Applies to: ICP F9MAE / G9MAE modulating variable-speed condensing gas furnaces (060, 080, 100, 120 kBtu/h)

Likely causes

• Low or medium pressure switch stuck open
• Disconnected or blocked pressure tubing
• Improper pressure switch wiring
• Low inlet gas pressure (if LGPS used)
• Plugged condensate drain
• Water in vent pipe (sagging)

Test and repair steps

1. Check each pressure switch tube is connected and clear.
2. Check pressure switch wiring against the wiring diagram.
3. Flush collector box and clean condensate trap/drain; fix sagging vent pipe.
4. If LGPS used, verify inlet gas pressure 4.5 to 13.6 in. w.c. (natural gas).
5. Replace the stuck-open switch.

Models that show this code

6 models in ICP (F/G)9MAE Modulating Furnace

Other codes on the same units

• 3+5 Gas valve fault (modulating valve)
• 4 Limit circuit fault
• 4+1 Blower motor fault
• 4+2 Inducer motor fault
• 5 Abnormal flame-proving signal
• 6 Ignition proving failure
• 6+1 Ignition lockout
• 7 Limit circuit lockout