Oct 24th 2026
Suburban Tankless Water Heater Troubleshooting: IW60 / Nautilus Error Codes and ST-42 / ST-60
TROUBLESHOOTING · TANKLESS
Suburban Tankless Water Heater Troubleshooting: IW60 / Nautilus Error Codes and ST-42 / ST-60
What each IW60 error code means, the minimum flow it needs, the reset, and freeze protection, plus what’s different on the newer ST-42/ST-60.
The short version
- IW60 codes E1–E6 lock out; E7, E9 and EC recover on their own once fixed.
- Reset: switch off 5 seconds, then on, or with the Control Center, turn the faucet off and on.
- It needs at least 0.5 GPM of flow and 30 psi inlet pressure (ST-42/60: 0.7 GPM).
- Gas supply should be 11–14 in. water column; 12V supply 10.5–14 V.
Covers these models
Suburban on-demand (tankless) RV water heaters. Code table below is from the IW60 service manual.
IW60 error codes
| Code | Meaning | What to check | Recovery |
|---|---|---|---|
| E1 | Ignition fault (no flame after igniting) | Gas on and tank full, 11–14 in. WC supply, air in line, electrode (1/8 in. gap) | Lockout |
| E2 | Flame lost during operation | Gas supply and pressure, low flow, flame sensor | Lockout |
| E3 | False fire (flame signal before start or after stop) | Gas valve not closing, flame sensor | Lockout |
| E4 | Water overheating (outlet over 90°C) | Low or interrupted flow, outlet sensor | Lockout |
| E5 | Thermal switch open (overheat) | Overheat switch / ECO; find why it overheated | Lockout |
| E6 | Air pressure switch fault | Blower, pressure switch and its hose, vent blockage | Lockout |
| E7 | Inlet water sensor fault | Inlet thermistor or wiring | Auto |
| E9 | Water sensor fault | Thermistor or wiring | Auto |
| EC | Communication failure | Control Center cable and connections | Auto |
From Suburban’s IW60 service manual. Codes like “E12” or “E62” seen online appear to be misreadings of the manual and aren’t real codes.
Step-by-step: no hot water
STEP 1
Reset it
Switch off 5 seconds and back on, or turn the faucet off and on with the Control Center. After a propane tank change, light a stove burner first to purge air.
STEP 2
Check flow
It won’t fire below 0.5 GPM. Open the faucet more, clean aerators and shower heads, remove flow restrictors and don’t use a shower head’s pause button. Inlet pressure must be at least 30 psi.
STEP 3
Check for cold water mixing into the hot side
If it needs much more than 0.5 GPM to light, cold is bleeding into the hot line. Close the water heater bypass valve, outside shower valves and any unused fixtures.
STEP 4
Check gas and 12V
Gas 11–14 in. WC; 12V 10.5–14 V at the unit. The IW60 draws about 2.5 A and uses two 5 A fuses.
Still locking out with the same code?
Ignition or flame
Check the electrode/flame probe, gas valve and gas supply.
Air or overheating
Check the blower and pressure switch hose (E6), and flow and sensors (E4/E5). Suburban’s parts include the module board, flow sensor and Control Center.
Freeze protection and winterizing
- IW60 freeze protection: the burner cycles when water drops below 40°F until it’s above 50°F, but only with gas and 12V on.
- Draining: power, gas and pump off, open faucets, remove the service panel and open the red drain valve at the rear (IW60RL: also turn the black handle 1/4 turn counterclockwise).
- Descale yearly: Suburban says to flush the heat exchanger once a year with an approved descaler (Suburban kit 521163).
- ST-42/60: blow out with compressed air at 40 psi max; freeze protection cycles the burner below 41°F.
IW60 drain and freeze parts
ST-42 / ST-60 differences
The newer ST models need 0.7 GPM minimum, run 8,000–42,000 or 8,000–60,000 BTU/h, lock out after 3 failed tries or 20 minutes of continuous running, and draw under 10 A at 12V. Suburban’s user manual doesn’t publish an error code list for them, so contact Suburban (423-775-2131) or us with the code you see.
Parts for this repair
Suburban 521135 IW60 Nautilus Module BoardView part →
Suburban 161291 IW60 Control Center (white)View part →
Suburban 233237 IW60 Water Flow SensorView part →
Suburban 172022 IW60 Drain Valve (red knob)View part →
Suburban 172025 IW60 Frost Protection Drain TubingView part →
Suburban 161250 IW60 Pressure Relief ValveView part →Shop by category: Suburban parts, Tankless water heaters.
FAQ
What does E1 mean on a Suburban tankless water heater?
Ignition fault: no flame was detected after trying to light. Check propane, gas pressure (11–14 in. WC), air in the line and the electrode.
How do I reset a Suburban IW60?
Switch it off for 5 seconds and back on. With the Control Center, turn the faucet off and on or press OFF then ON.
What is the minimum flow for a Suburban tankless?
0.5 GPM for the IW60 and 0.7 GPM for the ST-42/ST-60.
Why does my tankless need the faucet wide open to light?
Usually cold water is mixing into the hot line through a bypass valve or outside shower. Close them.
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 Suburban’s IW60 service and installation manuals, IW60/IW60RL and ST-42/60 operation guides and the Suburban parts manual.