Between heating elements, wire harnesses, sensors, and control boards, one particularly thorough verified reviewer ended up replacing nearly every serviceable component on their RTEX unit over about two years of ownership. Their detailed account, while an unusually extensive case, actually doubles as a useful map of exactly which parts exist and can be individually replaced on this unit.
The most commonly replaced parts on a Rheem RTEX-24 include the heating elements (three total, individually replaceable), the wire harness connecting components, temperature and flow sensors, and in more serious cases, the control board or “motherboard,” all of which are documented as individually serviceable based on verified owner repair experiences. Most of these parts are available through Amazon and other retailers, either as genuine Rheem parts or compatible equivalents.
Heating Elements
The most frequently replaced part, based on verified reviews, is the heating element itself. The RTEX-24 uses three copper immersion elements, and multiple reviewers describe successfully replacing a single failed element in about 30 minutes using basic tools, after properly cutting power at the breaker and shutting off water supply.
Compatible replacement elements, including options that work across multiple RTEX models (RTEX-18, RTEX-24, RTEX-27) and equivalent EcoSmart units, are readily available:
HE 90240 Heating Element Replacement for Rheem RTEX-18/24/27 - View on Amazon
Wire Harness
At least one detailed verified review describes a wire harness failure severe enough to cause arcing and melting, tripping the breaker before more serious damage occurred. Following that failure, the reviewer contacted Rheem directly and received a replacement wire harness. This underscores that while replaceable, wire harness issues should be treated seriously given the safety implications, and any replacement work involving the harness itself is best handled by, or at minimum inspected by, a licensed electrician.
Sensors (Flow and Temperature)
Verified reviews document both flow sensors and inlet/outlet water temperature sensors as replaceable components, generally addressed when the unit displays specific error codes (like E5) related to sensor readings rather than actual heating capacity. In the detailed multi-part failure case referenced earlier, the reviewer received replacement sensors directly from Rheem after their wire harness issue didn’t fully resolve the underlying problem.
Control Board (Motherboard)
In more serious failure cases, the unit’s control board, sometimes referred to as the motherboard, may need replacement. This is a more involved repair than a simple element swap and represents a bigger portion of the unit’s overall value, so it’s worth confirming with Rheem support or a professional whether a control board replacement makes more financial sense than replacing the entire unit, depending on your unit’s age and remaining warranty status.
Service Valve Kits
Beyond components that fail and need replacing, service valve kits are a proactive addition many owners install (or retrofit) specifically to make future maintenance, especially descaling, significantly easier without shutting off water to the entire home:
Tankless Water Heater Service Valve Kit - View on Amazon
When to Repair vs Replace the Whole Unit
If you’re facing a cascade of failures similar to the detailed case referenced throughout this guide, multiple sensors, a wire harness, and a control board all failing within a relatively short window, it’s worth stepping back and calculating whether continued part-by-part repair actually makes financial sense compared to simply replacing the entire unit, particularly if it’s still within a warranty period that would cover a full replacement.
For single, isolated component failures (most commonly, a single heating element), individual part replacement remains the more cost-effective and faster solution based on the patterns across most verified reviews.
For the step-by-step process specifically for the most commonly replaced part, see our heating element replacement guide.
Rheem RTEX-24 24kW 240V Electric Tankless Water Heater - Check Current Price on Amazon
The Bottom Line
The Rheem RTEX-24’s most commonly replaced parts, heating elements, wire harnesses, sensors, and occasionally the control board, are all individually serviceable and available through Amazon and other retailers. Single component failures are usually worth repairing individually, while a cascade of multiple failures may signal it’s time to evaluate full unit replacement instead.
Frequently Asked Questions
What parts commonly fail on the Rheem RTEX-24? Based on verified reviews, heating elements are the most commonly replaced part, followed by wire harnesses, flow and temperature sensors, and in more serious cases, the control board.
Can I buy replacement heating elements for the Rheem RTEX-24? Yes, compatible replacement elements, including options that work across multiple RTEX models, are readily available through Amazon and other retailers.
Is it safe to replace the wire harness myself? Given the safety implications documented in at least one verified review involving arcing, wire harness work is best handled by, or at minimum inspected by, a licensed electrician.
What does it mean if my Rheem RTEX-24 needs a new control board? This indicates a more serious internal electronic failure, and given the cost and complexity, it’s worth confirming with Rheem support whether replacing the control board or the entire unit makes more financial sense.
Does Rheem provide replacement parts directly? Based on at least one detailed verified review, yes, the owner received replacement wire harness and sensor parts directly from Rheem after contacting the company about their unit’s issues.
Are service valve kits necessary for the Rheem RTEX-24? They’re not strictly required, but they make future maintenance, especially descaling, significantly easier by allowing you to isolate the unit without shutting off water to your entire home.
How much do replacement parts typically cost? Costs vary by specific part; heating elements are generally the most affordable individual component, while a control board replacement represents a larger portion of the unit’s overall value.
Should I repair or replace my entire unit if multiple parts fail? If you’re facing a cascade of multiple component failures within a short period, it’s worth calculating whether continued repair makes financial sense compared to replacing the entire unit, especially if it’s still under warranty.
Can I use parts from other brands on my Rheem RTEX-24? Some compatible replacement elements are designed to work across multiple brands’ similar tankless models, though always confirm compatibility with your specific unit before purchasing.
Where should I buy replacement parts? Amazon offers a wide selection of both genuine Rheem parts and compatible equivalents, making it a convenient and reliable source for most commonly needed replacement components.
References
- Verified Amazon customer reviews detailing real component failures and replacement experiences for the Rheem RTEX-24, accessed July 2026: https://www.amazon.com/dp/B01MS9DVEE
- Amazon.com replacement parts listings for Rheem RTEX-compatible components, accessed July 2026