This guide shows how to quickly diagnose a failed control thermostat in a Dometic / Atwood RV water heater. These troubleshooting steps apply to most gas/electric combination models. A failed control thermostat will typically cause:

• no gas operation

• no electric operation

• complete water heater shutdown

Important: This test must be performed with the water heater completely cold. If the water heater is already up to operating temperature, the thermostat will be open normally, which can lead to incorrect test results.