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4

Rheem Water Heater

Severity: Moderate

Source: OnlyErrorCodes.com — Every error code. One place.

Rheem Water Heater Code 4 — Thermopile Fix

What Does This Error Mean?

Code 4 means the thermopile is generating too little voltage to keep the gas valve open. Clean the thermopile tip first — carbon deposits are the most common cause. Replace it if cleaning does not restore voltage above 400 mV.

Affected Models

  • Rheem Performance Gas
  • Rheem Performance Plus Gas
  • Rheem XR90
  • Rheem Natural Gas Tank Models

Common Causes

  • Carbon deposits on thermopile tip reducing output voltage
  • Thermopile reaching end of service life (5–10 years)
  • Weak pilot flame not fully heating the thermopile
  • Loose or corroded thermopile wire connections at the gas valve

How to Fix It

  1. Confirm the pilot flame is lit and burning blue.

    A yellow, flickering, or small pilot flame does not heat the thermopile enough to generate adequate voltage. A healthy pilot flame wraps around the thermopile tip.

  2. Clean the thermopile tip.

    Turn off gas and allow the unit to cool. Gently clean the thermopile tip — the metal rod beside the pilot flame — with fine steel wool. Carbon and oxide deposits reduce its voltage output significantly.

  3. Check the thermopile wire connections.

    Trace the two thermopile wires to the gas valve. Ensure both terminals are tight and free of corrosion. Even slight corrosion adds resistance that reduces the effective voltage.

  4. Test thermopile output voltage.

    With the pilot lit, measure DC millivolts across the thermopile terminals with a multimeter. A healthy reading is 650–850 mV. Below 400 mV means the thermopile is failing and should be replaced.

  5. Replace the thermopile if voltage is low.

    Rheem-compatible thermopiles are available from plumbing suppliers. Match the connector type and probe length to the original. The replacement is a direct swap on most models.

When to Call a Professional

If cleaning does not resolve Code 4 and the unit is under warranty, contact Rheem or a licensed plumber before replacing components.

Frequently Asked Questions

What is the difference between the thermopile and thermocouple on a Rheem?

A thermocouple generates just enough voltage to hold the pilot valve open. A thermopile generates higher voltage to power the gas valve and electronic controls. Code 4 relates specifically to the thermopile.

How long does a Rheem thermopile last?

Typically 5–10 years. Hard water and corrosive atmospheres (near pools, for example) can shorten thermopile life due to accelerated tip corrosion.