Goodman GMVM970803BN Error Code E5: Open Fuse

What Does Code E5 Mean?

An E5 code on the Goodman GMVM970803BN means the fuse on the integrated control module has blown, cutting off low-voltage power. That fuse protects the control board and the entire 24-volt control circuit from damage when a short circuit occurs. Once it blows, the furnace has no control power and cannot operate at all. A telltale sign on this communicating furnace is that a ComfortNet thermostat displays "Battery Power" — it is no longer receiving 24 volts from the furnace transformer because the blown fuse has opened that path.

The cause is almost always a short in the low-voltage (24-volt) wiring rather than the fuse simply wearing out. This furnace's transformer feeds the control board, thermostat, and any outdoor unit or accessories through that 24-volt circuit, so a short anywhere along it will pull enough current to open the fuse. Common culprits are bare thermostat wires touching each other or a grounded surface, insulation damaged by rodents or by rubbing against a sharp cabinet edge, or a miswired thermostat or accessory. Because the fuse is the protective element, its blowing usually means it did its job — the real fault is the short it was protecting against.

This is different from the E5 being a board failure or a power-supply problem. The board and transformer are typically fine; the fuse is a sacrificial 3-amp automotive-type fuse specifically meant to blow first. Replacing it without finding the short just sacrifices another fuse, since the new one blows the moment power is restored into the faulted circuit.

What You'll Notice

• The dual 7-segment display shows E5 (and the display itself may be dark if control power is fully lost)
• A ComfortNet communicating thermostat reads "Battery Power" or otherwise acts as if it lost furnace power
• The furnace is completely unresponsive — no inducer, no ignition, no blower on a call for heat
• A newly installed fuse blows again immediately when power is restored
• The problem may have started right after thermostat, accessory, or outdoor-unit wiring was worked on

Common Causes

How This Is Diagnosed

A technician's goal is to find the short before spending fuses. After replacing the blown fuse with the correct 3-amp automotive-type fuse, they isolate the circuits: the thermostat wires and any accessory or outdoor-unit wiring are disconnected, and then reconnected one circuit at a time while watching whether the fuse holds. The circuit that blows the fuse is the one containing the short.

Once the faulted branch is identified, the technician inspects that wiring run for bare conductors, chafed insulation, rodent damage, or a miswired connection at the thermostat or accessory, and repairs it. Only after the short is corrected is the final fuse installed and the furnace returned to service. This is low-voltage electrical fault-finding, which is why it is a professional task rather than a DIY fuse swap.

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:

• A replacement fuse blows again as soon as power is restored
• The thermostat shows "Battery Power" and the furnace has no control power
• The code appeared after thermostat, accessory, or outdoor-unit wiring was recently changed
• Any low-voltage wire looks chewed, bare, pinched, or discolored

✓ Verified against manufacturer service manual — March 2026