Troubleshooting the E-20 M GMU Relay Failure (MV) Error Code

Overview

The E-20 M – GMU Relay Failure (MV) error occurs when the GMU (Gas Management Unit) internal relay K4, which controls power to the main gas valve, does not produce the expected output signal.

The failure is typically caused by:

• An open or failed K4 relay on the GMU board.

• A wiring fault between the GMU K4 output and the main gas valve.

• A loose, damaged, or disconnected electrical connection.

Call Avoidance Steps

Before scheduling a service visit, have the customer perform the following checks:

1. Power cycle the appliance.

   • Turn the appliance OFF.

   • Wait 30 seconds.

   • Restore power and check for the error.

If the error does not return, continue normal operation and monitor the unit.

If the error returns, service is required.

Field Troubleshooting

Recommended Parts

• GMU (Gas Management Unit) Board

Recommended Tools

• Digital Multimeter

• Basic Hand Tools (screwdrivers, nut drivers, etc.)

Troubleshooting Steps

1. Inspect wiring between the GMU K4 output and the main gas valve.

• Check for loose, disconnected, pinched, damaged, or burned wiring.

• Check connector pins for corrosion or poor terminal contact.

• If wiring damage is found, repair or replace the wiring and retest the appliance.

• If wiring is intact, continue to Step 3.

2. Verify 24 VAC Output from GMU to Main Gas Valve Coil.

   • Measure 24 VAC on the GMU K4 output and the main gas valve connection.

   • If voltage is not present, replace GMU.

   • If voltage is present, verify wiring connections on GMU to Main Valve Coil.

Other Troubleshooting

Although uncommon, the following conditions may also cause an E-20 M fault:

• Intermittent wiring failure

  • Wiring may test good when stationary but open under vibration or heat.

  • Perform a wiggle test while monitoring continuity or voltage.

• Poor connector pin contact

  • Connector terminals may be spread, corroded, or not fully seated.