How to Wire Rheem RTEX 13 Electric Tankless Water Heater Step by Step

Before servicing the RTX 13 electric heater, disconnect power at the circuit breaker and verify all current is dead using a non-contact voltage tester. Failure to isolate the unit properly risks severe electrical shock or component damage. The 240V model draws up to 54 amps–ensure wiring and breakers meet NEC article 422 requirements for continuous loads.

The terminal block accepts dual 6-gauge copper conductors (minimum 75°C rating) and a separate 10-gauge ground. Terminals are labeled L1, L2, and GND–mismatching phases trips the overcurrent protection. For single-phase hookups, bridge L1 and L2 with a jumper if using a 120V supply, but note output drops to 3 kW (10,236 BTU/h).

Field-installed thermostats require a 18-gauge stranded wire with a 1.5 mm² cross-section. Route control wires away from condensate lines and high-voltage cables to prevent interference. The red wire connects to the upper thermostat post (R), the white to the lower (W)–reversing polarity disables heating. Test continuity with a multimeter set to ohms after installation.

For pool applications, install a 30 mA ground fault circuit interrupter upstream of the heater. Check local codes–some jurisdictions mandate splicing the neutral at the unit. If using external timers or pumps, size conductors for a combined load: a 1.5 HP pump at 115V adds 13 amps to the circuit.

After securing connections, torque terminal screws to 12 in-lbs using a calibrated driver–over-tightening strips threads, under-tightening causes arcing. Recheck all junctions after 24 hours of operation; thermal cycling shifts loose connections. If nuisance tripping occurs, inspect for moisture ingress or improperly secured bonding jumpers.

Electrical Connection Guide for RTEX 13 Tankless Unit: Step-by-Step Instructions

Ensure the power supply circuit matches the unit’s specifications: 240V AC, 60Hz, with a dedicated 30-amp double-pole breaker. Connect the black and red leads to the breaker terminals, securing each with a torque screwdriver set to 18 in-lbs. Attach the green grounding wire to the designated ground bar in the service panel, verifying no corrosion or loose contacts exist before energizing. Failure to adhere to these torque values risks overheating or arc faults, leading to premature component failure.

The internal junction box contains three terminal posts labeled L1, L2, and ground. Route the black wire from the power line to L1, the red to L2, and the bare copper or green wire to the ground post. Use 10 AWG copper conductors for the entire run, as thinner gauges or aluminum wiring cannot handle the 54A maximum draw under load. Avoid splicing wires inside the unit; external junction boxes must comply with NEC 314.16, providing at least 6 cubic inches of fill space per conductor.

Before closing the cover, test continuity between each hot terminal and ground using a multimeter. Resistance readings should exceed 1MΩ; anything lower indicates insulation breakdown or moisture ingress, requiring immediate correction. Install a surge protector rated for 240V/60A transients, preferably with Type 2 SPD certification, to safeguard the microcontroller from voltage spikes. Improper surge protection reduces lifespan by 30-45% based on field data from installations in high-lightning regions.

Final verification includes a cold-water flush at 6 GPM for 30 seconds to purge air from the heat exchanger, followed by a temperature rise test. Measure inlet and outlet temps with a calibrated thermometer; the delta should stabilize between 25°F and 45°F at 1.5 GPM flow. If readings deviate, recalibrate the flow sensor via the service menu, ensuring the dip switches (DS1-DS4) align with the factory default setting for 240V operation. Misconfigured dip switches trigger erratic heating cycles or error code 12, necessitating a full reset.

Decoding the RTEX 13 Electrical Connection Color Standards

Start by identifying the blue conductor–this is your dedicated neutral line and must connect directly to the corresponding terminal in the installation manual’s power distribution guide. Verify continuity before securing the terminal screw to prevent intermittent faults or overheating.

Attach the black lead to the live input; this carries the primary voltage from the circuit breaker. Ensure the wire gauge matches the system’s amperage requirements–typically 10 AWG for the RTEX 13 configuration–to avoid voltage drop or insulation damage. Confirm the breaker size aligns with local electrical codes, usually 25–30 amps for this model.

The red wire serves as the secondary live conductor for split-phase setups or additional power legs in specific installations. Trace its path to avoid mixing it with the black wire; reversing these can trip breakers or damage internal relays. If the unit lacks dual-voltage capability, cap the red wire with a wire nut and label it for future reference.

Green or bare copper wire grounds the system–connect it to the chassis ground screw or the green terminal block without fail. Test for proper grounding with a multimeter; readings should show near-zero resistance to earth. Skipping this step exposes users to shock hazards and voids manufacturer warranties.

White or gray wires, if present, often indicate low-voltage control circuits for thermostats or external sensors. Cross-check these with the schematic’s legend–incorrect pairing can prevent the unit from powering on or cause erratic performance. Isolate these wires from high-voltage lines using appropriate wire nuts or terminal blocks rated for the expected load.

Inspect all conductors for nicks, fraying, or discoloration before finalizing connections. Replace compromised wires immediately; even minor damage increases resistance and reduces efficiency. Use crimp connectors or soldered joints for secure, long-term reliability–tape-wrapped connections degrade over time and risk short circuits.

After assembly, power the circuit and monitor the display for error codes. Hold a non-contact voltage tester near the terminal block to confirm proper polarity–flashing alerts may indicate reversed lines. If the unit fails to activate, revisit each connection against the color-coded reference; most faults trace back to misaligned or loose terminals.

Step-by-Step Electrical Hookup for RTEX 13 Unit Setup

Shut off the main power supply at the breaker panel before handling any live circuits. Verify zero voltage using a non-contact voltage tester on all terminals.

Locate the electrical junction box on the right side of the appliance. Remove the cover plate by unscrewing the two Phillips-head fasteners securing it.

Preparing the Supply Lines

• Strip 5/8 inch of insulation from the ends of two 10-gauge copper conductors (black and white) using wire strippers.
• Insert a 30-amp double-pole circuit breaker into the service panel, matching the breaker’s amperage to the unit’s nameplate rating (240V, 13kW).
• Connect the black supply wire to the breaker’s upper terminal and the white supply wire to the neutral bus bar. If grounding is separate, attach a green or bare copper wire to the grounding bus.

Run the supply cables through the knockout hole in the junction box. Secure them with a romex clamp tightened to prevent cable pull.

Terminal Attachments

1. Match the black conductor to the L1 terminal and the white conductor to the L2 terminal inside the junction box. Torque each screw to 20 in-lbs using a torque screwdriver.
2. Attach the grounding wire to the green screw terminal marked PE. Ensure the connection is tight; loose grounding poses a shock hazard.
3. Tuck excess wire neatly into the box, avoiding sharp edges that could damage insulation.

Replace the cover plate and secure it with the original screws. Turn the breaker back on and observe the digital display for error codes–E1 or flashing lights indicate miswiring.

Verify proper operation by setting a test temperature of 110°F. After 90 seconds, check for consistent output at the nearest hot water tap; fluctuations suggest incorrect terminal connections.

Seal any gaps around the electrical entry point with silicone caulk to prevent moisture ingress, which can corrode terminals over time.

Identifying and Resolving Installation Faults in RTX 13 Electric Tankless Systems

Check voltage polarity at terminals L1 and L2 before powering the unit. Reverse connections trigger a E3 error code, even if incoming voltage reads 240V. Use a multimeter in AC mode–probes on terminal screws with leads disconnected–to verify correct phase alignment. If readings drop below 210V, inspect the circuit breaker for partial tripping or loose wire clamps within the junction box. Replace any corroded breaker contacts to restore stable voltage delivery.

• Unplug power, remove the front cover, and examine heating element resistance. A functional 27kW model measures 12-15 ohms across both elements connected in series; deviations signal element failure or internal shorting. Disconnect wires from the control board to isolate faulty elements for replacement.
• Ensure all grounding screws make solid contact. Loose grounding causes intermittent E2 or E4 faults. Verify ground wire continuity from the unit’s chassis to the main panel–maximum resistance 0.5 ohms. Clean oxidation from copper surfaces with sandpaper and re-secure connections.
• Recalibrate flow sensors if fluctuating temperature outputs occur. Remove inlet filter, rinse sediment buildup, then reset factory sensor settings via dip-switch sequence: hold SET, toggle UP/DOWN to FCT 0, release SET.

If error E5 persists despite proper calibration, inspect the high-limit thermistor for physical damage. Replace the 10k NTC sensor if resistance exceeds ±5% of nominal values–measure at 25°C for baseline accuracy. Secure new thermistors with thermal paste to prevent air gaps during remounting.