The thermal cut off (TCO) – sometimes called a thermal fuse or energy cut off – is the last line of defense against a dangerous overheating event in your Atwood RV water heater. It sits in the wiring circuit between the incoming power and the thermostat, monitoring the temperature in the burner compartment at all times. If temperatures reach 190°F – indicating something has gone seriously wrong with heat dissipation – the TCO's internal element permanently opens the circuit, cutting all power to the ignition system and shutting down the water heater before damage or a dangerous situation can develop.2-Pack190°F RatingReplaces 94398 / 93866
Why does it trip? The single most common cause of TCO failure in Atwood water heaters isn't a defect in the heater – it's a blocked burner tube or flue tube. Spiders and wasps are drawn to the warm, sheltered space of an RV water heater compartment during storage and off-season periods. They build nests inside the main burner tube and flue passage, blocking the airflow that carries combustion heat safely out of the unit. When that pathway is obstructed, heat backs up into the burner compartment rather than exiting through the flue, and temperatures rise rapidly until the TCO trips. The 94398/93866 TCO is doing exactly what it was designed to do – but once it's tripped, it must be replaced, and the burner tube must be cleared before the heater is placed back in service.
Permanently opens circuit at dangerous overtemp
Keep a spare – never wait for a reorder
Fits all Atwood "E" suffix electronic ignition models
In-line on power wire – simple two-wire installation
The TCO is a thermal fuse, not a circuit breaker or a resettable thermostat. When the internal element reaches 190°F, a small fusible link inside permanently melts and opens the circuit. There is no reset button, no way to reclose it, and no way to test it back into service. This is by design – a permanently open circuit provides absolute certainty that the heater cannot re-energize until a technician has physically inspected and replaced the component, ensuring that whatever caused the overtemp condition has been identified and corrected before the heater runs again.
Do not attempt to bypass the TCO. It is the only electrical protection between the ignition system and a sustained overheating event. Bypassing it eliminates that protection entirely and creates a genuine fire hazard.
Atwood water heater TCOs trip frequently because of a problem that has nothing to do with the heater itself: spiders and wasps. The burner tube on Atwood direct ignition water heaters has an open end that faces the outside of the RV through the access door. During storage – even short periods between camping trips – spiders and mud dauber wasps enter this opening and build nests inside the tube. The nests are often invisible from the outside and don't require much material to partially or fully block the tube. When the heater fires with a blocked burner tube or flue, combustion gases can't flow freely, heat accumulates in the burner compartment instead of exiting through the flue, and temperatures climb quickly to the TCO's trip point. Before replacing the TCO: Always inspect and clear the main burner tube, orifice, and flue passage of any spider webs, wasp nests, or debris. Installing a new TCO without clearing the blockage will result in the new TCO tripping as well. Many RVers add a bug screen to the burner tube access area as preventive maintenance.
A tripped TCO produces a specific symptom: the water heater does not ignite, and the "check" or fault light illuminates on the wall switch or control panel. In models without a fault light, the heater simply will not respond to the on switch at all – no clicking, no attempt to ignite, no error code – because the circuit that powers the ignition board has been permanently opened upstream.
A simple continuity test across the two terminals of the TCO with a multimeter confirms diagnosis without ambiguity: a good TCO shows continuity (a closed circuit); a failed TCO shows open (no continuity).
The TCO is installed in series on the incoming power wire to the thermostat. Replacement is straightforward: disconnect power, locate the existing TCO on the wiring harness inside the burner compartment (typically mounted near the burner tube or heat exchanger), disconnect the two wire connectors, and connect the new TCO in the same position. The replacement wire connections in the 94398 kit allow for direct reconnection to the existing harness connectors.
Before reinstalling: Thoroughly inspect and clear the burner tube, orifice, and flue passage. The cause of the original overtemp event must be resolved or the new TCO will trip as well.
1. Disconnect power – Turn off the water heater switch inside the RV and disconnect shore power or turn off the converter before opening the burner compartment 2. Inspect the burner tube and flue – Before replacing the TCO, shine a light through the full length of the main burner tube, check the orifice opening, and inspect the flue exit. Clear any spider webs, mud dauber nests, or debris with compressed air or a pipe cleaner 3. Locate the TCO – The existing 93866/94398 TCO is in the burner compartment wiring, typically near or clamped to the burner tube or heat exchanger housing. It has two wire leads with push-on connectors 4. Test with multimeter – Confirm the existing TCO is open (no continuity) before removing it to rule out other wiring issues 5. Replace – Disconnect the two connectors, remove the TCO from its mounting clip, connect the new NBK 20327 TCO in the same position and orientation 6. Restore power and test – Reconnect power, turn on the water heater, and observe ignition. Normal ignition confirms the repair is complete
The TCO is a maintenance-interval part for any RV water heater owner. If it has tripped once due to a spider or wasp nest blockage, it's likely to encounter the same conditions again during future storage periods unless a permanent screen solution is installed. Keeping a spare TCO on board means that when the heater fails to ignite at the start of a camping trip, you can diagnose, clear the blockage, and replace the TCO on the spot rather than spending the trip without hot water while waiting for a part to arrive. The cost difference between one and two is minimal; the peace of mind is significant.
G6A Series: G6A-2E, G6A-3E, G6A-4E, G6A-6E, G6A-7E, G6A-8E, G610-3E G10 Series: G10-1E, G10-2E, G10-3E GC6A Series: GC6A-7E GC6AA Series: GC6AA-7E, GC6AA-8E, GC6AA-9E, GC6AA-10E GC10 Series: GC10-1E, GC10-2E, GC10A-2E, GC10A-3E, GC10A-4E GCH6 Series: GCH6-4E, GCH6-6E, GCH6-7E GCH6A Series: GCH6A-7E, GCH6A-8E, GCH6A-9E, GCH6A-10E GCH10A Series: GCH10A-2E, GCH10A-3E, GCH10A-4E GH6 Series: GH6-3E, GH6-4E, GH6-6E, GH6-7E, GH6-8E, GH610-3E GH10 Series: GH10-1E, GH10-2E, GH10-3E, GH10A-3E EXT Series: G9-EXT, G16-EXT, GE9-EXT, GE16-EXT, GEH9-EXT, GEH16-EXT WH Series: WH-6GA, WH-6GEA, WH-9GEA Rule of thumb: If your model number ends in "E" or is an EXT/WH series, this TCO is compatible. If your model number does NOT end in "E" (pilot ignition models), this part is not applicable.
The NBK 20327 (94398/93866) thermal cut off is designed exclusively for Atwood direct spark ignition (DSI) / electronic ignition water heaters – models with an "E" suffix in the model number. Atwood pilot ignition water heaters (models without an "E" suffix, such as G6A-2, GC6A-7, GH6-4) use a different safety system – a thermocouple-based gas control valve with an internal energy cut off – and do not use this TCO. Installing this part on a pilot ignition model is incorrect and will not function as intended. If you are unsure whether your unit is DSI or pilot ignition, check the model number on the data plate inside the water heater access door. If the model ends in "E" – it's DSI. If it doesn't – it's pilot.
Replacing the TCO without finding and clearing the cause of the overtemp condition will result in the new TCO tripping as well. Before installing the new unit, inspect and clear the main burner tube, orifice, and flue passage of all spider webs, wasp nests, and debris. Use compressed air to blow through the full length of the burner tube and confirm clear passage before restoring power.
Set a multimeter to continuity or resistance mode. Probe both terminals of the TCO. A good TCO reads continuity (closed). A tripped TCO reads open (no continuity) – confirming it needs replacement. This test takes 30 seconds and confirms the diagnosis without guesswork.
When servicing a tripped TCO, inspect and consider replacing: Thermostat / ECO (Atwood 91447) – The ECO thermostat is a resettable high-limit switch that works alongside the TCO. If both have been exposed to overtemp conditions, the ECO may need resetting or replacement. Igniter / Spark Probe (NBK 12452 / Atwood 93868) – If the burner tube has been blocked long enough to trip the TCO, inspect the spark probe tip for carbon buildup or damage from incomplete combustion events. Burner Tube Screen / Bug Guard – Adding a fine mesh screen over the burner tube access opening is the most effective long-term prevention against repeat spider and wasp nest blockages.
• Disconnect all power before servicing – Turn off the water heater at the wall switch, disconnect shore power, and wait for the unit to cool before opening the burner compartment • Never bypass the TCO – Bypassing the thermal cut off eliminates fire protection from the circuit; a bypassed TCO creates a genuine fire hazard and must never be done under any circumstances • Find and fix the root cause – A TCO trip is a symptom, not the problem. The blockage or condition that caused it must be identified and corrected before the heater is returned to service • DSI/electronic ignition models only – Verify your model number ends in "E" before ordering; pilot ignition models use a different safety system • Aftermarket product – This is an NBK aftermarket replacement, not an Atwood/Dometic OEM part; it is not manufactured by or affiliated with Atwood Mobile Products or Dometic