State Water Heater E42 Error Code — What It Means
Error code E42 does not appear in available State Water Heaters service documentation or diagnostic charts. State heat pump models use built-in diagnostics that require a multimeter and the model-specific fault code table to interpret properly. Without the exact model number and control platform, it is impossible to determine what E42 indicates or which component has failed. If your display shows E42, the first step is to locate your model and serial number on the rating plate and cross-reference the code in the installation and service manual for that specific unit.
Some water heaters from other manufacturers use error 42 to indicate exhaust or air pressure switch faults, but State’s fault code assignments vary by model and fuel type. Do not assume E42 means the same thing across brands. If you recently installed a Honeywell smart thermostat or Wi-Fi module on your water heater system, E42 on that device means the router did not assign an IP address and is unrelated to water heater operation.
Common Causes
- Misread code or wrong manual The code may be E4 or 42 without the E prefix, or you are consulting documentation for a different model series.
- Control board from a different platform Replacement or retrofit boards from other manufacturers may display codes that do not match State’s published legend.
- Aftermarket Wi-Fi module error Honeywell and similar add-on controllers use E42 to signal a router or DHCP failure, not a water heater fault.
- Unpublished or prototype code Some pre-production or region-specific units may display codes not yet included in widely available service literature.
Step-by-Step Fix
- Locate the rating plate on the side of the tank and write down the complete model number, serial number, and fuel type (electric, gas, or heat pump).
- Download the installation and service manual from the State Water Heaters website or contact State customer service with your model number to request the correct diagnostic code table.
- Power cycle the unit by turning off the circuit breaker or gas valve for 60 seconds, then restore power and observe whether the code clears or changes.
- Check for aftermarket controllers such as Wi-Fi modules or smart thermostats. If a Honeywell or similar device shows E42, verify your router DHCP settings and rerun the wireless setup.
- Use a multimeter to test voltage at the control board and measure resistance across any sensors called out in your model’s manual. State heat pump units require multimeter diagnostics rather than code-only troubleshooting.
- Inspect wire connections at the control board, high-limit switch, and any pressure or temperature sensors for corrosion or loose terminals.
- Contact State technical support at 1-800-365-0024 with your model number and E42 description to confirm the code definition and recommended tests before ordering parts.
Parts Often Needed
| Part | Notes |
|---|---|
| Control board or user interface | Amazon | Only if State support confirms E42 indicates a board fault for your specific model. |
| Multimeter | Amazon | Required for tracing voltage and resistance on State heat pump and electronic-control models. |
When to Call a Pro
Call a licensed plumber or water heater technician if you cannot locate a manual that lists E42 for your model, if multimeter readings fall outside the ranges in your service guide, or if the code persists after power cycling and connection checks. Because E42 is not documented in widely available State literature, professional diagnosis with manufacturer support is the safest path to avoid replacing the wrong component. If your unit is still under warranty, contact State or your installer before performing any repairs to preserve coverage.