E1 Error on AO-SMITH NNLP-110-H NG Tankless Water Heater — Fix Guide

• Source: Official ao-smith service manual
• Reviewed by: Geo Technical Editorial
• Published: March 1, 2026
• Updated: March 1, 2026

Safety notice: Start with user-safe checks only. Do not open sealed refrigerant systems, inspect gas-train components, or work on energized high-voltage parts unless you are qualified to service this appliance.

Error E1 on ao-smith : No ignition — burner failed to light. Follow the troubleshooting steps below to diagnose and fix this tankless-water-heater issue. ## What Error Code E1 Means on a ao-smith NNLP-110-H NG Error E1 on the NNLP-110-H NG tankless water heater indicates the gas burner failed to establish a flame during the ignition trial. The unit will lock out after three failed attempts, requiring a manual reset. When E1 appears, the ao-smith tankless water heater pauses normal operation to protect internal components from potential damage. Not every E1 fault requires a professional engineer — many are resolved through careful inspection and routine maintenance. Work through each diagnostic step below in sequence, starting with the simplest check, to identify the root cause efficiently before considering part replacement or arranging a service call. ## Symptoms - Cold water flows through when hot is demanded

• E1 on display; unit is in lockout
• Igniter click heard but no sustained burner flame
• Unit shows error immediately after water flow starts ## Common Causes - No ignition — burner failed to light ## Tools You May Need - Gas pressure gauge (professional)
• Flashlight
• Screwdrivers ## Step-by-Step Repair Guide | Step | Action | Result | |------|--------|--------| | 1 | Check gas supply — confirm main gas valve and unit service valve are fully open. | Done — continue to step 2 if the issue persists. | | 2 | Verify minimum gas pressure: 4–5 in. WC for natural gas, 8–11 in. WC for propane. | Done — continue to step 3 if the issue persists. | | 3 | Inspect igniter electrodes for carbon buildup; clean with a soft-bristle brush. | Done — continue to step 4 if the issue persists. | | 4 | Clean the flame sensor rod with fine steel wool (light pass only, do not scratch). | Done — continue to step 5 if the issue persists. | | 5 | Reset the unit by pressing the reset button (or cycling power for 10 seconds). | Done — if the fault remains, contact a qualified technician. | ## Safety Precautions Repeated failed ignition cycles can accumulate gas in the heat exchanger. Allow 5 minutes of ventilation between reset attempts. ## Estimated Repair Time and Difficulty Most tankless water heater error code E1 faults can be assessed and addressed in 30–90 minutes using the steps above. The diagnostic process requires only basic tools: a multimeter and standard screwdrivers cover the majority of checks described here. If a replacement part is required, allow 1–5 working days for delivery. A trained technician with access to the correct diagnostic equipment will typically resolve this type of fault within a single service visit. ## When to Call a Technician Contact a ao-smith authorised service technician if: the fault persists after following all the steps above; if PCB-level or refrigerant-circuit work is required; or if you are not comfortable working with electrical or mechanical components. When calling, have the full model number, the error code displayed, and a brief description of any sounds or symptoms you noticed before the fault appeared — this helps the technician prepare the correct parts and tools. ## Frequently Asked Questions Q: Can a gas pressure drop at peak demand cause E1? Yes — running multiple gas appliances simultaneously can drop pressure below the minimum for ignition. Check incoming pressure during peak demand conditions. Q: How do I reset an E1 lockout? Press the Reset button on the unit or switch the dedicated service switch Off then On. If E1 returns after 3 resets, call a technician. ### Is it safe to keep using my ao-smith with error E1? If error E1 does not indicate an immediate safety hazard such as a gas leak, electrical short, or water flooding, you can continue limited use while monitoring the appliance. However, running the tankless-water-heater with an active error code increases the risk of further damage. Address the underlying issue as soon as possible. For high-severity errors, disconnect the appliance and contact a qualified technician. ### How much does it cost to fix error E1 on a ao-smith ? Repair costs for error E1 on the ao-smith tankless-water-heater depend on the root cause. DIY fixes such as cleaning filters, resetting the unit, or reconnecting loose wires cost nothing beyond basic tools. If a component replacement is needed, parts and labor from a certified technician are the main expenses. Contact a ao-smith-authorized service provider for an accurate estimate based on your specific situation. ### What does error code E1 mean on a ao-smith tankless-water-heater? Error code E1 on ao-smith tankless-water-heater models indicates No ignition — burner failed to light. This error is detected by the appliance’s internal diagnostic system and displayed to alert the user that attention is needed. Refer to the troubleshooting steps above for guidance on resolving this issue. ### Is it safe to keep using my ao-smith with error E1? If error E1 does not indicate an immediate safety hazard such as a gas leak, electrical short, or water flooding, you can continue limited use while monitoring the appliance. However, running the tankless-water-heater with an active error code increases the risk of further damage. Address the underlying issue as soon as possible. For high-severity errors, disconnect the appliance and contact a qualified technician. ### How much does it cost to fix error E1 on a ao-smith ? Repair costs for error E1 on the ao-smith tankless-water-heater depend on the root cause. DIY fixes such as cleaning filters, resetting the unit, or reconnecting loose wires cost nothing beyond basic tools. If a component replacement is needed, parts and labor from a certified technician are the main expenses. Contact a ao-smith-authorized service provider for an accurate estimate based on your specific situation. ### What does error code E1 mean on a ao-smith tankless-water-heater? Error code E1 on ao-smith tankless-water-heater models indicates No ignition — burner failed to light. This error is detected by the appliance’s internal diagnostic system and displayed to alert the user that attention is needed. Refer to the troubleshooting steps above for guidance on resolving this issue.