Rheem Water Heater Not Heating: Diagnosis and Fixes

Common Symptoms

• No hot water at any tap despite the unit appearing to run
• Lukewarm water only — never reaching the set temperature
• Pilot light won't stay lit on gas Performance or Prestige models
• EcoNet app showing E1, E5, E6, or E9 fault code
• Hot water runs out much faster than usual (lower element failed)
• Popping or rumbling sounds during heating cycles (sediment buildup)

Most Likely Causes

1. 1

   Thermocouple Degradation — Gas Models (Most Common)

   On Rheem Performance and Prestige gas water heaters, the thermocouple is a thin probe that sits in the pilot flame and generates a small millivolt signal (should be ≥17mV) to keep the gas valve open. As the thermocouple ages, its output voltage drops — a degraded thermocouple may generate only 10–12mV, which is insufficient to hold the gas valve open. The pilot lights briefly then goes out when you release the control knob. Test with a multimeter in millivolt mode: a healthy thermocouple reads 25–35mV. Below 17mV means replace it. Rheem SP20005 is the OEM thermocouple for most Performance series gas models.

2. 2

   Failed Heating Element — Electric Models (E1, E9 Code)

   Rheem electric water heaters (PROE40, PROE50, Performance Platinum series) use two 240V heating elements — upper and lower. The upper element heats first; when it fails (E1 or E9 code), no water in the tank reaches temperature. The lower element handles recovery heating; when it fails, you run out of hot water quickly. Test with a multimeter on resistance mode: a functional 4500W 240V element reads 12–16Ω (formula: R = V²/W = 240²/4500 ≈ 12.8Ω). An OL (open) reading means the element is burned out. Rheem SP10552 is a compatible OEM replacement element.

3. 3

   Tripped High-Limit Reset Button (Electric Models)

   Rheem electric water heaters have a red thermal cutoff (TCO) reset button on the upper thermostat behind the upper access panel. If the tank overheats — due to a failing thermostat, shorted element, or blocked dip tube — the TCO trips and cuts power to both elements. No hot water results even if both elements are functional. Press the red button firmly until it clicks, restore power, and wait 45 minutes. If it trips again, find the overheat cause before resetting.

4. 4

   Failed Upper or Lower Thermostat (E5, E6 Code)

   Rheem error codes E5 (upper thermostat open circuit) and E6 (lower thermostat open circuit) indicate a failed thermostat. The upper thermostat controls the upper element and contains the TCO. The lower thermostat receives a signal from the upper thermostat to activate the lower element for recovery heating. Test both thermostats with a multimeter in continuity mode — each should show continuity across its active terminals when below its setpoint temperature.

5. 5

   Sediment Buildup Insulating the Lower Element

   In hard water areas, calcium and magnesium deposits accumulate on the lower heating element over years of use. Heavy sediment insulates the element surface, causing it to run hotter and eventually burn out. The symptom is a gradual reduction in hot water quantity, loud popping or rumbling during heating, and eventually no hot water. Flush 2–3 gallons from the tank drain valve every 6 months to slow sediment accumulation. If the lower element is already coated, replace it and flush the tank completely.

6. 6

   Anode Rod Depletion

   Rheem water heaters ship with a sacrificial magnesium or aluminum anode rod that protects the tank lining from corrosion. When the rod corrodes down to the steel core wire (typically after 3–5 years in hard water), tank corrosion accelerates rapidly — leading to discolored water, rotten-egg smell, and eventually tank failure. Inspect the anode rod annually via the hex fitting on top of the tank. Camco 11562 is a compatible replacement anode rod for most Rheem tank sizes.

Quick DIY Checks

1. 1Step 1 — Check EcoNet fault log and error codes: if your Rheem water heater has EcoNet Wi-Fi connectivity (Performance Platinum, ProTerra), open the EcoNet app and navigate to the fault history. Note any active error codes: E1 = temperature sensor fault, E5 = upper thermostat open, E6 = lower thermostat open, E9 = heating element failure. For gas models, check the digital display on the gas control valve for fault codes. For units without connectivity, look for a blinking LED on the gas valve or digital controller — blink patterns indicate fault types. Write down the code before proceeding so you know which component to test first.
2. 2Step 2 — Gas models: inspect and test the pilot and thermocouple: set the gas control knob to PILOT. Press and hold the knob while clicking the igniter — hold for a full 60 seconds after the pilot lights. Slowly release. If the flame goes out immediately, the thermocouple is generating insufficient voltage. Test with a multimeter set to millivolts: clip one probe to the thermocouple body and the other to the tip terminal at the gas valve while the pilot is lit. A healthy Rheem thermocouple reads 25–35mV. Below 17mV means replace it. Rheem SP20005 is the OEM replacement thermocouple for most Performance series models — it threads into the gas valve and clips into the pilot assembly. Turn gas off and wait 15 minutes before replacing.
3. 3Step 3 — Electric models: test heating elements with a multimeter: turn off BOTH poles of the water heater circuit breaker. Remove the upper access panel (2–4 screws) and fold back the insulation to expose the thermostat and upper element terminals. Use a non-contact voltage tester to confirm zero voltage before touching any wiring. Disconnect both wire leads from the upper element terminals. Set multimeter to resistance (Ω) and probe both element terminals: a functional 4500W 240V element reads 12–16Ω. OL (open) = burned out, replace Rheem SP10552. Also test element-to-tank-body (ground): should read OL — any continuity means the element insulator has failed and the element must be replaced. Repeat for the lower element using the lower access panel.

1. 4Step 4 — Check and reset the high-limit thermostat (TCO): with power off, locate the red reset button on the upper thermostat behind the upper access panel. If the button is popped out, press it firmly until you hear a click. Restore the circuit breaker and wait 45–60 minutes for the tank to heat. If the TCO trips again, there is an overheat condition — a shorted element drawing excess current or a stuck thermostat. Test both elements for a shorted condition (resistance near 0Ω). Also test upper thermostat continuity: with power off, probe the two upper terminals — should show continuity when the water temperature is below the setpoint.
2. 5Step 5 — Inspect and replace the anode rod, flush sediment: attach a garden hose to the drain valve at the bottom of the tank and route it to a floor drain or outside. Open a hot water tap inside the house to break vacuum. Open the drain valve and flush 2–3 gallons — note whether the water is cloudy, gritty, or rust-colored. Cloudy = mineral sediment, rust = tank corrosion. For the anode rod: locate the hex fitting on top of the tank (may be under insulation or a cover plate). Use a 1-1/16 inch socket to remove it. A rod corroded down to the steel core wire or coated in calcium nodules needs immediate replacement. Camco 11562 is a compatible magnesium anode for most Rheem models.
3. 6Step 6 — Test and exercise the TPR valve: the temperature and pressure relief (TPR) valve is mounted on the side of the tank near the top, with a discharge pipe running down toward the floor. With the cold water supply on and the unit at operating temperature, lift the TPR valve lever briefly (just 1–2 seconds) — you should hear a rush of water, then it should reseat and stop dripping. A valve that drips after being exercised or won't release when lifted should be replaced (Watts 240A or equivalent, rated for your tank pressure and temperature). Never cap or plug a TPR discharge pipe — this is a critical safety device.

Repair vs Replace

Recommended Tools & Parts

• Rheem SP20005 Thermocouple

  OEM replacement thermocouple for Rheem Performance and Prestige gas water heaters. Generates millivolt signal to hold the gas valve open when the pilot is lit. Replace when output drops below 17mV. Universal thread fitting for most Rheem gas valve assemblies.

  $15–$25

  Buy on Amazon →

• Rheem SP10552 Heating Element

  OEM replacement 4500W 240V screw-in heating element for Rheem electric water heaters including Performance and Performance Platinum series. Test with multimeter before replacing (OL = burned out, 12–16Ω = good). Requires 1.5-inch element socket wrench to install.

  $20–$35

  Buy on Amazon →

• Camco 11562 Anode Rod

  Magnesium anode rod compatible with most Rheem tank water heaters. Sacrificial rod that protects the tank lining from corrosion — inspect annually in hard water areas, replace every 3–5 years or when corroded to the steel core wire.

  $20–$35

  Buy on Amazon →

• Klein MM400 Multimeter

  Digital multimeter for testing heating elements (resistance), thermocouple output (millivolts), and thermostat continuity. Required for accurate water heater diagnosis. Klein MM400 is a reliable mid-range meter well suited for appliance work.

  $25–$40

  Buy on Amazon →

Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.

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