Oct 24th 2026
Atwood / Dometic Water Heater Thermostat and ECO: How to Test and Replace
PARTS GUIDE · THERMOSTAT & ECO
Atwood / Dometic Water Heater Thermostat and ECO: How to Test and Replace
Atwood heaters have separate controls for the gas side and the electric side. Here’s what each part does, the temperatures they open at, and how to test them.
The short version
- Gas side (DSI): front-mount thermostat/ECO 91447. The thermostat opens at about 140°F; the ECO opens above 180°F.
- Thermal cut-off 93866 is a separate one-shot safety that trips at 190°F. It doesn’t reset; replace it.
- Electric side: 110V thermostat/ECO 91873. Thermostat 140°F, ECO above 170°F, with a manual reset button.
- Atwood’s element is 1400 W (not Suburban’s 1440 W).
Covers these models
Atwood/Dometic DSI water heaters. Check your model; Dometic WH-series temperatures aren’t published.
Which part does what
| Part | Side | What it does |
|---|---|---|
| 91447 thermostat/ECO | Gas (12V) | Front-mount. Thermostat opens about 140°F; ECO opens above 180°F |
| 93866 thermal cut-off | Gas (12V) | One-shot at 190°F; trips from a blocked burner or flue tube |
| 91873 thermostat/ECO | Electric (110V) | Screw-in element models: thermostat 140°F, ECO above 170°F, manual reset |
| 92097 element | Electric | 1400 W, 110–120V |
Temperatures from the Atwood service manual.
Testing the electric side (Atwood’s procedure, power off)
STEP 1
Turn off 120V
Turn off the breaker and the electric switch. Remove the cover over the thermostat and element terminals.
STEP 2
Press the ECO reset
Press the manual reset button on the ECO first.
STEP 3
Check continuity across the ECO
Continuity = good. Open after resetting = replace the thermostat/ECO.
STEP 4
Check continuity across the thermostat
With the water cool it should be closed. Open = replace. If the water isn’t hot enough, make sure the thermostat sits flat against the tank.
STEP 5
Check the element
Across the element terminals: open = burned out. From a terminal to the element flange: any continuity means it’s shorted to ground. Atwood doesn’t publish an ohm value; by the formula, a 1400 W element at 120V works out to about 10 ohms (our calculation).
Which part failed?
Replace the 110V thermostat/ECO
Replace the element
Drain the tank first. See how to replace an element.
Testing the gas side
Atwood’s service manual just says to check the DSI thermostat for voltage or continuity and replace it if necessary. With the water cool and power on, you should have 12V through the 91447 to the board when it calls for heat. Check the 93866 thermal cut-off for continuity too: open means it tripped, and you should find out why (a spider nest or blocked flue) before you replace it.
Gas side parts
Water too hot or not hot enough?
- Not hot enough: reseat the thermostat flat against the tank (Atwood’s first fix), check the bypass valve is closed, and run gas and electric together for faster recovery.
- Too hot / ECO trips: a thermostat that doesn’t open lets the water overheat until the ECO trips. Replace the thermostat.
- After an ECO trip on gas: let the water cool, switch off for at least 30 seconds, then on.
Parts for this repair
Dometic 91447 Front Mount ECO/Thermostat Kit (DSI)View part →
Dometic/Atwood 93866 Thermal Cut-Off KitView part →
Dometic/Atwood 91873 Thermostat/ECO, 110V ACView part →
Dometic/Atwood 92097 AC Heating Element (1400 W)View part →
Dometic/Atwood 93849 Element Relay, 110VView part →Shop by category: Atwood parts, Dometic parts.
FAQ
What temperature does an Atwood water heater thermostat open at?
About 140°F on DSI and screw-in electric models. The DSI ECO opens above 180°F and the electric ECO above 170°F.
Is 93866 a thermostat?
No. It’s a one-shot thermal cut-off that trips at 190°F, usually from a blocked burner or flue. Replace it after fixing the cause.
What wattage is an Atwood water heater element?
1400 W (reduced from 1500 W in 1996).
Where is the reset button on an Atwood water heater?
On the electric-side ECO under the terminal cover. Press it in before testing.
Not sure which part fits? Contact us with your model and serial number from the data plate and we’ll confirm it before you order.
From the Atwood water heater service manual, Atwood/Dometic installation and operating manuals (MPD 93755/93756, Dometic 94035 and 3317866) and dometic.com. Element ohms are our calculation.