Payne PG96VTA Error Code 43: Low-Heat Pressure Switch Open While High-Heat Pressure Switch Is Closed
What Does Code 43 Mean?
Code 43 (four short flashes followed by three long flashes) flags a contradictory state between this two-stage furnace's two pressure switches: the high-heat pressure switch is closed while the low-heat pressure switch is open. Normally the low-heat switch should be closed whenever there is enough draft to close the high-heat switch, so this combination signals a fault on the low-heat side.
On a condensing furnace the most common cause is a plugged condensate drain affecting the pressures the switches sense. Other causes are a low-heat pressure switch stuck open, disconnected or obstructed sensing tubing on the low-heat switch, improper pressure-switch wiring, or low inlet gas pressure where a low gas pressure switch (LGPS) is used.
Code 43 belongs to the same draft-proving family as code 31 (high-heat switch) and code 32 (low-heat switch), but it specifically catches the two switches disagreeing rather than one simply failing to close. Because the diagnosis spans the condensate system, tubing, wiring, and the switch itself, it is technician work.
What You'll Notice
- The furnace fails to run properly or drops out, with staging behaving abnormally
- The amber LED flashes four short flashes followed by three long flashes (code 43)
- Little or no reliable heat while the control sorts out the conflicting switch inputs
- Signs of a condensate backup, such as water at the drain or trap
- The problem may be intermittent if the low-heat tubing is partially obstructed or the switch sticks
Common Causes
How This Is Diagnosed
A technician checks the condensate drain and trap first on this condensing furnace, then inspects the low-heat pressure switch's sensing tubing for disconnection or obstruction, verifies the pressure-switch wiring, and tests whether the low-heat switch is stuck open. Where an LGPS is fitted, inlet gas pressure is also checked.
Because the fault sits in the combustion draft-proving and condensate system, this is professional work. A homeowner can note an obvious condensate backup or a disconnected tube, but the switch and tubing diagnosis should be left to a technician.
When to Call a Professional
This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:
- The furnace shows code 43 and will not heat reliably
- Water is backing up at the condensate drain or trap
- The code is intermittent, suggesting a partially obstructed tube or a sticking low-heat switch
- The furnace was recently serviced and the pressure-switch tubing or wiring may have been disturbed
Frequently Asked Questions
What does code 43 mean on my Payne PG96VTA?
It means the low-heat pressure switch is open while the high-heat switch is closed — a contradictory state that points to a fault on the low-heat side, most often a plugged condensate drain, a stuck switch, or disconnected tubing.
How is code 43 different from code 32?
Code 32 is simply the low-heat switch failing to close; code 43 is the two switches disagreeing — low-heat open while high-heat is closed. Both involve the low-heat draft-proving side and often share the same causes.
Can a clogged drain really cause a pressure switch code?
Yes. On a condensing furnace, a backed-up condensate drain disturbs the pressures the switches sense, which can leave the low-heat switch open and trigger code 43. Clearing the drain is a common part of the fix.
✓ Verified against manufacturer service manual — March 2026