Goodman GMVM970803BN Error Code EF: Auxiliary Input Open

What Does Code EF Mean?

An EF code on the Goodman GMVM970803BN indicates that the auxiliary input circuit on the integrated control module is open. The auxiliary input terminals exist so an external safety device — most commonly a condensate overflow float switch, sometimes a secondary limit — can shut the furnace down when it detects a problem. If no such device is used, a jumper wire must be installed across the terminals to complete the circuit. When the board sees that circuit open, it interprets it as a tripped safety and refuses to start.

Because the GMVM97 is a high-efficiency condensing furnace, it produces liquid condensate every time it runs, and that water must drain away continuously. The most common EF scenario is a condensate problem: if a float switch is wired to the auxiliary input and the condensate drain clogs with algae, sludge, or mineral buildup, water backs up and lifts the float, opening the circuit. That is the safety system doing its job — stopping the furnace before overflowing water can damage the control board or the home. This ties EF to the drainage side of the same system that shows up in pressure-switch codes like E2 (low-stage pressure switch stuck open), where a blocked drain is one listed cause.

Less commonly, the jumper across the auxiliary terminals was removed during a service call and not reinstalled, or the wiring to an external safety device has come loose or been damaged. Unlike the gas-side safety codes on this board, EF does not by itself indicate a combustion problem — but because it can involve a float switch, a limit device, or bare control wiring, confirming what is actually connected is a technician's job.

What You'll Notice

• The dual 7-segment display on the control board shows EF and the furnace produces no heat
• There may be standing water in the condensate drain pan or a backed-up drain line if a float switch tripped
• The furnace may have shut down shortly after a period of heavy condensate production in cold weather
• If the code appeared right after a service visit, an accessory jumper or safety-device wire may have been left disconnected
• The furnace stays off and does not cycle even though the thermostat is calling for heat

Common Causes

How This Is Diagnosed

A technician first determines what is actually wired to the auxiliary input, because the fix depends on it. If a condensate float switch is connected, they check the drain pan and drain line for standing water and a blockage — a clogged condensate line that has tripped the float is the typical finding, and clearing it (often with a wet/dry vacuum or compressed air) lets the float drop and the circuit close.

If no external device is connected, the technician confirms that the required jumper is present and secure across the auxiliary terminals, since a missing jumper produces the same open circuit. With power off, they also inspect the auxiliary wiring for loose or damaged connections. The furnace should not be forced to run by bypassing a genuine safety device — if a float switch is present, the underlying condensate blockage is corrected rather than jumpered out.

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:

• There is standing water in the condensate pan or the drain line appears clogged
• You are unsure whether a float switch, secondary limit, or jumper is connected to the auxiliary input
• The EF code appeared right after a service visit and wiring may have been left disconnected
• The code returns after the condensate drain has been cleared, suggesting a recurring drainage or wiring issue

✓ Verified against manufacturer service manual — March 2026