Fault codes / Suburban tankless
Suburban IW60 and ST tankless water heater fault codes
Suburban's on-demand heaters (IW60 and the later ST series; RL models add a recirculation pump) fire on water flow and modulate gas to hold the set temperature. The display shows an E-code when it stops. Most no-hot-water calls are flow or gas, not the heater: do the tankless flow test first.
Suburban tankless code E0
Outlet temperature probe open or shorted. Reseat the probe plug, ohm the thermistor, replace it.
Suburban tankless code E1
Ignition failure: no flame after 3 tries. Light the stove first to prove gas. Check LP pressure under load, the igniter gap and the ground. Air in the line after a bottle change takes several tries.
Suburban tankless code E2
False flame: flame sensed before startup. Cycle it off, wait 5 seconds, on. If it returns, a stuck gas valve or a flame sense circuit fault.
Suburban tankless code E3
High limit (ECO) tripped. Open the small access panel on the unit and press the reset button on the thermal disc. Find out why it overheated: scale, low flow, a set point too high, or a fan problem.
Suburban tankless code E4
Inlet temperature sensor open or shorted. Reseat, ohm, replace.
Suburban tankless code E5
Fan failure: no speed signal. Clean the fan blades, check the fan plug and 12V at the fan. Replace the fan if it has power and no signal.
Suburban tankless code E6
Over temperature at the outlet. Water is being mixed at the faucet so hot flow drops too low. Run the hot side wide open and lower the set point. Scale raises outlet temperature too.
Suburban tankless code E7
Gas valve circuit open or shorted. Check the valve plug and wiring; ohm the valve coils.
Suburban tankless code E8
Pressure switch stuck closed or disconnected. Check the hose to the pressure switch for kinks and water. Confirm the exhaust and intake are clear. Reported at high altitude.
Suburban tankless code E9
Recirculation pump will not prime (RL models). Air in the loop. Bleed the recirculation line and check the pump.
Suburban tankless code En
Ran continuously for more than 20 minutes. Turn the water off, wait 5 seconds, back on. A faucet left running or a leaking toilet valve keeps it firing.
Suburban tankless code EC
Lost communication with the controller. Check the display cable at both ends.
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Full field guide: Suburban IW60 and ST tankless water heater
Codes come from the maker manuals and public service sheets. Your model's own chart always wins, and LP and 120 volt work belongs to a qualified technician.