American Water Heater Not Working: Diagnosis and Repair Guide

Common Symptoms

• American water heater produces absolutely no hot water — tank stone cold
• American ProLine gas: pilot light will not light or will not stay lit
• American ProLine gas: Honeywell WV8840 green LED is flashing — error code visible
• American ProLine electric: circuit breaker for water heater has tripped
• American ProLine electric: breaker is on but no hot water at all — elements not heating
• American Voltex heat pump: display shows fault code (E1, E4, E5, or others)
• American ProLine gas: pilot lights but main burner will not fire when demand calls
• Rumbling or popping from tank followed by complete loss of heat (sediment-triggered TCO trip)

Most Likely Causes

1. 1

   American ProLine Gas: Pilot Outage — Thermocouple Failure

   The most common reason an American ProLine gas water heater stops working is a failed thermocouple causing the pilot to extinguish. The thermocouple is a heat-sensing probe positioned in the pilot flame; it generates a small DC millivoltage (healthy range: 25–35mV) that holds the gas valve open. American ProLine gas models use a Honeywell WV8840 combination gas valve, identifiable by its round green LED indicator window. A failed thermocouple produces less than 17mV, and the gas valve shuts off all gas flow as a safety measure — both pilot and main burner. The Honeywell WV8840 LED will flash 4 times if thermopile voltage is too low (models with thermopile instead of thermocouple). The WV8840 will simply not hold pilot if thermocouple output drops below the valve threshold. Replace with American/AO Smith part 9005502 (thermopile) or a universal 36-inch thermocouple for thermocouple-based models.

2. 2

   American ProLine Gas: Honeywell WV8840 LED Flash Codes

   American ProLine gas water heaters with the Honeywell WV8840 gas valve communicate faults via the green LED light on the valve face. The LED flash pattern must be counted carefully — count the flashes, then the pause, then the next sequence. Key codes: 1 flash = thermopile voltage low (pilot lit but thermopile output below 325mV — borderline thermocouple/thermopile); 2 flashes = thermal switch (TCO) open circuit — a safety switch has tripped due to excessive temperature; 3 flashes = gas valve internal fault (valve should be replaced); 4 flashes = gas valve temperature high (overheating condition — check for blocked flue/air starvation); 7 flashes = gas valve failed, replace the WV8840 assembly. Steady ON (no flashing) = normal operation. A rapidly blinking LED or one that is extinguished with no pilot = no thermopile/thermocouple voltage reaching the valve.

3. 3

   American ProLine Gas: Thermal Switch (TCO) Open Circuit

   American ProLine gas water heaters have a thermal cutout (TCO) thermal switch mounted on the burner assembly or gas valve. This is a one-shot safety device that opens permanently if the burner area exceeds a safe temperature threshold — commonly triggered by a blocked flue, excessive sediment causing the burner to overheat, or inadequate combustion air around the unit. The Honeywell WV8840 will flash 2 times when the TCO circuit is open. The TCO does NOT reset by itself — on American ProLine gas models, the reset is part of the gas valve assembly. If the WV8840 shows 2 flashes, shut off the gas, verify the flue is clear and the draft hood is unobstructed, then follow the Honeywell reset procedure for that valve model (typically a button hold sequence on the gas control knob). If it trips again immediately after reset, investigate the underlying overheating cause before proceeding.

4. 4

   American ProLine Electric: ECO Thermal Cutout Tripped

   American ProLine electric water heaters have a manual-reset ECO (Energy Cut-Out) safety switch on each thermostat — one upper, one lower. If the water temperature exceeds approximately 180°F (thermostat runaway, element short, or both thermostats set too high), the ECO trips and cuts power to all heating elements. Unlike a circuit breaker, a tripped ECO produces NO visible sign at the breaker panel — the breaker appears on but the heater does not heat. Diagnosis: remove both access panels (upper and lower), fold back the insulation — there is a small red or white reset button on each thermostat. If either button is popped out, it has tripped. Press firmly to reset. If it trips again within the heating cycle, the thermostat has failed and must be replaced — repeated ECO trips without a root cause investigation can indicate an element shorted to ground.

5. 5

   American ProLine Electric: Failed Heating Element or Shorted Circuit

   American ProLine electric models use 240V dual-element systems. A failed element (open circuit — most common mode) stops heating but doesn't typically trip the breaker. A shorted element (element wire contacts the steel sheath — ground fault) WILL trip the circuit breaker and may also trip the ECO. The typical sequence for a shorted element: breaker trips, is reset, and trips again within minutes once heating load begins. Confirm with a resistance test: with the 240V breaker OFF, disconnect both element wires, measure resistance between the two terminals (should be 12–16 ohms for a 4500W element) and between each terminal and the metal element sheath (should be infinite/OL). Any reading between terminal and sheath indicates a ground fault — replace the element.

6. 6

   American Voltex Heat Pump: E-Series Fault Codes

   The American Voltex hybrid electric heat pump water heater has a digital display that shows fault codes when a fault is detected. Key fault codes: E1 = inlet thermistor failure (temperature sensor on cold inlet); E4 = upper thermistor failure; E5 = lower thermistor failure; FE = fan error (fan motor failed or obstructed — check for debris around the unit top); CE = compressor error (compressor overload or failure); SE = sensor error (evaporator thermistor). For most E-series codes, the Voltex will fall back to electric-resistance-only operation — the heat pump is disabled but the unit still heats water. Press the Mode button for 3 seconds to attempt a fault reset; if the code returns, the sensor or component indicated needs replacement. CE (compressor) faults typically require a certified HVAC technician.

Quick DIY Checks

1. 1Step 1 — American ProLine gas: read the Honeywell WV8840 LED code before touching anything: on your American ProLine gas water heater, locate the Honeywell WV8840 gas valve — the round green LED indicator is on the front face of the valve, near the temperature dial and PILOT/ON/OFF knob. Count the flashes carefully: count individual flashes in a burst, note the pause length, then count the next burst. 1 flash = low thermopile voltage; 2 flashes = TCO open (safety switch tripped); 3 flashes = gas valve fault; 4 flashes = gas valve overtemp; 7 flashes = gas valve failure. Steady on = normal. Write down the code before proceeding — this determines your repair path. If the LED is off and the pilot is out, the issue is likely a failed thermocouple or thermopile with no voltage reaching the valve.
2. 2Step 2 — American ProLine gas: relight the pilot and test thermocouple millivolts: follow the lighting instructions on the American water heater's rating label. Turn the gas control knob to PILOT. Depress the knob fully and press the igniter button repeatedly until the pilot lights. Hold the knob down for 45–60 seconds to allow the thermocouple to heat. Slowly release — if the pilot extinguishes immediately, the thermocouple is not generating enough millivolts. To measure: connect a multimeter set to DC millivolts to the thermocouple lead wires at the gas valve (TH and TH/TP terminals) while the pilot is lit. Healthy reading: 25–35mV; minimum acceptable: 17mV. Below 17mV means the thermocouple must be replaced. Use American/AO Smith part 9003972 (thermocouple) or 9005502 (thermopile) as appropriate to your model.
3. 3Step 3 — American ProLine gas: reset a tripped TCO (2-flash code on WV8840): if the Honeywell WV8840 shows 2 flashes, the thermal cutout circuit is open. First, investigate the cause: check that the flue vent pipe is clear of obstructions, that the draft hood above the tank is unobstructed, that the unit has adequate combustion air (at least 50 cubic feet of air space per 1000 BTU/hr of input), and that sediment rumbling hasn't been causing extended burn cycles. To reset: turn the gas control knob to OFF and allow 5 minutes for the burner to cool. On some American ProLine models, the TCO reset is accessible through the burner access door at the bottom of the tank — there is a small red reset button on the burner assembly. Press firmly until it clicks. Restore gas and attempt to relight. If it trips again on the next heating cycle, flue blockage or a failed thermostat requires professional inspection.

1. 4Step 4 — American ProLine electric: reset tripped ECO thermal switches: turn off the 240V circuit breaker for the water heater. Remove the upper access panel (typically held by 2 screws or snap clips). Fold back the foam insulation to expose the upper thermostat. Locate the ECO reset button — it is a small red or white push-button on the center of the thermostat body, slightly raised when tripped. Press firmly until you feel a click. Replace the insulation and panel. Repeat this process at the lower access panel for the lower thermostat. Restore the circuit breaker. Wait 60–90 minutes for the electric unit to fully recover. If the ECO trips again within the heating cycle, the thermostat has failed (runaway) and must be replaced — do not continue resetting without replacing the faulty thermostat.
2. 5Step 5 — American ProLine electric: test heating elements for open or shorted circuits: with the 240V breaker OFF, remove both access panels. Fold back insulation. Disconnect both wires from the upper element and measure resistance between the two terminals — expect 12–16 ohms for a 4500W 240V element (lower wattage elements will measure higher). Also test between each terminal and the element sheath (the metal body of the element): should be infinite/OL. Reconnect upper wires and repeat for lower element. Open circuit (OL between terminals) = failed element, replace. Near-zero reading terminal-to-sheath = element shorted to ground, replace, and also check why the ground fault occurred (excessive scale causing hot spots). Replace with Camco 02142 (4500W screw-in) or the OEM equivalent for your American ProLine model.
3. 6Step 6 — American Voltex heat pump: reset fault codes and verify clearances: on the American Voltex display, note the fault code. Press and hold the Mode button for 3 seconds to attempt a fault reset. Before restoring operation, verify: (a) the unit has 700+ cubic feet of clear air space around it (basement, garage — a closet installation will starve it of air); (b) the air filter at the bottom front of the unit is clean — remove and rinse under warm water, dry completely; (c) nothing is blocking the air intake or exhaust vents at the top. If the fault code is FE (fan): inspect for physical obstructions at the fan housing (spiders, debris). If CE (compressor): contact a licensed HVAC technician — the compressor requires refrigerant system work. Most other codes (E1, E4, E5, SE) indicate thermistor sensor failures that can be replaced by an experienced DIYer.

Repair vs Replace

Recommended Tools & Parts

• American/AO Smith Thermocouple 9003972

  OEM thermocouple for American ProLine gas water heaters (thermocouple-based models). 36-inch lead. Replace when pilot won't hold after 45 seconds of button depression, or when millivolt test shows below 17mV. Fits American ProLine gas with Honeywell WV8840 valve.

  $12–$20

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• American/AO Smith Thermopile 9005502

  OEM thermopile for American ProLine gas models with thermopile (no standing pilot igniter models). Generates 300–750mV to power the Honeywell WV8840. Replace when WV8840 shows 1-flash code (low voltage) and thermopile millivolt test is below 325mV.

  $25–$45

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• Camco 02142 4500W Screw-In Heating Element

  Universal screw-in 4500W 240V element for American ProLine electric water heaters. Replace when resistance test shows open circuit (OL) between terminals or terminal-to-sheath ground fault. Includes new element gasket. Drain tank fully before removal.

  $18–$35

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• American/AO Smith Upper Thermostat Kit 100110321

  Replacement upper thermostat assembly for American ProLine electric water heaters. Includes ECO thermal cutout. Replace when upper ECO trips repeatedly within a single heating cycle despite element testing good, or when upper zone overheats without demand.

  $20–$40

  Buy on Amazon →

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

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