State Water Heater E170 Error Code — What It Means
E170 is an overheat fault. Your State water heater’s control system has detected that water temperature exceeded its safety limit, so it locked out to protect the unit and your home. The controller saw a temperature reading above the allowed threshold and stopped normal operation to prevent damage or scalding.
This code typically signals a real problem with heat transfer, airflow, or sensing rather than a transient glitch. The fault can appear on both tank-type and tankless models, though the underlying causes differ slightly by platform.
Common Causes
- Scale or mineral deposits on the heat exchanger Buildup insulates the metal and prevents proper heat transfer, creating localized hot spots that trip the overheat sensor.
- Blocked or restricted vent or air intake Obstructions, disconnected sections, or debris in the vent system raise internal temperatures and can disturb combustion or heat removal.
- Faulty temperature sensor or thermistor A failing sensor may send an incorrect high reading to the control board, or it may read intermittently and trigger false overheat shutdowns.
- Restricted water flow through the unit A clogged inlet screen, partially closed isolation valve, or plumbing restriction can reduce flow and allow the heat exchanger to overheat.
- Recirculation pump creating abnormal flow conditions If a recirculation system is installed, improper pump operation or settings can generate unusual temperature or flow patterns that trip the limit.
Step-by-Step Fix
- Turn off hot-water demand at all fixtures and let the water heater cool for at least 30 minutes, then verify the E170 fault is still present on the display.
- Inspect the venting and air intake for blockages, damaged piping, disconnected joints, or debris, and clear any restrictions you find because airflow problems can directly cause overheating.
- Check water flow by cleaning the inlet screen or filter, confirming that both isolation valves are fully open, and verifying adequate supply pressure with no downstream restrictions.
- Flush and descale the heat exchanger following the manufacturer’s approved procedure if you see signs of mineral buildup or if you are in a hard-water area.
- Test the temperature sensor or thermistor using a multimeter to check resistance or continuity against the specifications in your model’s service manual, and replace it if readings are out of range or unstable.
- Reset the control board after correcting the underlying cause, then monitor the unit under normal load for at least one full heating cycle to confirm the code does not return.
- Escalate to advanced diagnostics if the fault recurs, including control-board input verification, combustion-air delivery checks, and internal safety-limit inspection.
Parts Often Needed
| Part | Notes |
|---|---|
| Temperature sensor (thermistor) | Amazon | Replace if resistance readings are out of spec or the sensor tests intermittent. |
| Inlet water filter or screen | Amazon | Clean or replace if clogged and restricting flow into the heater. |
| Heat exchanger assembly | Amazon | Required only if severe scale damage or overheating has permanently compromised heat transfer and flushing does not restore operation. |
| Control board | Amazon | Replace only after verifying all sensors and field wiring test correctly but the fault persists. |
When to Call a Pro
Call a licensed plumber or water-heater technician if you are not comfortable working with gas or electrical connections, if the fault returns after you have cleared blockages and flushed the system, or if you lack the tools to test sensors and control inputs. Overheat faults can indicate combustion or venting problems that require proper diagnostic equipment and code-compliant repairs. A qualified pro can perform a full descale service, verify safe combustion air delivery, and confirm that all safety limits are operating correctly before returning the unit to service.