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Appliance Error Codes

C8 Error on Rheem RTGH-95DVLN Tankless Water Heater — Fix Guide

Error C8 on Rheem : Inlet water temperature too cold or NTC1 thermistor fault. Follow the troubleshooting steps below to diagnose and fix this tankless-water-heater issue. ## What Error Code C8 Means on a Rheem RTGH-95DVLN Error C8 on the RTGH-95DVLN tankless heater means the inlet water temperature thermistor (NTC1) has an open or short circuit, or inlet water is below the minimum allowable inlet temperature. When C8 appears, the Rheem tankless water heater pauses normal operation to protect internal components from potential damage. Not every C8 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 - C8 on display; cold water flows through unheated

  • In very cold climates, may appear during winter if supply water is extremely cold
  • Thermistor failure confirmed by resistance check ## Common Causes - Inlet water temperature too cold or NTC1 thermistor fault ## Tools You May Need - Multimeter
  • Replacement NTC thermistor if needed ## Step-by-Step Repair Guide | Step | Action | Result | |------|--------|--------| | 1 | Check inlet water temperature at the supply line — if it is below 35°F (1.7°C), allow the supply to warm or insulate the supply pipe. | Done — continue to step 2 if the issue persists. | | 2 | Locate the NTC1 inlet thermistor (typically on the cold inlet pipe inside the unit). | Done — continue to step 3 if the issue persists. | | 3 | Disconnect and measure resistance at current inlet water temperature; compare to manufacturer’s chart. | Done — continue to step 4 if the issue persists. | | 4 | Replace the thermistor if it is out of specification. | Done — if the fault remains, contact a qualified technician. | ## Safety Precautions Shut off the cold water supply before accessing internal plumbing or sensor connections. ## Estimated Repair Time and Difficulty Most tankless water heater error code C8 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 Rheem 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: Does C8 only happen in winter? Thermistor failures can occur at any time. However, C8 from genuinely cold inlet water is more common in winter in cold climates. ### Is it safe to keep using my Rheem with error C8? If error C8 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 C8 on a Rheem ? Repair costs for error C8 on the Rheem 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 Rheem-authorized service provider for an accurate estimate based on your specific situation. ### What does error code C8 mean on a Rheem tankless-water-heater? Error code C8 on Rheem tankless-water-heater models indicates Inlet water temperature too cold or NTC1 thermistor fault. 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 Rheem with error C8? If error C8 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 C8 on a Rheem ? Repair costs for error C8 on the Rheem 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 Rheem-authorized service provider for an accurate estimate based on your specific situation. ### What does error code C8 mean on a Rheem tankless-water-heater? Error code C8 on Rheem tankless-water-heater models indicates Inlet water temperature too cold or NTC1 thermistor fault. 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.