521099 RV Water Heater Ignition Board | 12V PC Control Board Replacement 520820

521099 RV Water Heater Ignition Board – 12V PC Control Board Replacement 520820

The water heater ignition board (printed circuit control board) is the electronic module that manages the gas ignition sequence of your Atwood RV water heater. It controls the 12V spark ignition, flame sensing, gas valve operation, and safety lockout, ensuring reliable and safe operation of your water heater’s gas mode. When the ignition board fails, your water heater may fail to ignite on gas mode, not stay lit, or enter a safety lockout state.

This 521099 RV water heater ignition board is a 12V printed circuit (PC) control board designed as a direct replacement for the Atwood 520820 ignition board. It features reliable spark ignition, flame rectification sensing, gas valve control, 3-trial ignition with 30-minute lockout, and plug-and-play installation.

Compatibility

• Atwood 6-gallon water heaters: GC6AA-10E, GC6AA-9E, G6A-8E, G6A-7E, G6A-6E
• Atwood 10-gallon water heaters: GE16-EXT, GE9-EXT, G16-EXT, GC10A-4E
• Atwood water heaters with 12V electronic (spark) ignition
• Atwood AC/gas combination water heaters (gas mode ignition)
• Dometic WH-6GA, WH-9GA, WH-10GA water heaters (rebranded Atwood)
• Replaces board numbers: 521099, 520820, 520814, 91367, 31501, 33488, 33727
• Most Atwood/Dometic 6-10 gallon water heaters with 12V spark ignition

Specifications

How It Works

When you turn on the water heater’s gas mode (via the inside switch), 12V power is sent to the ignition board. The board initiates the ignition sequence: (1) Spark igniter activates, creating a 15kV spark at the electrode. (2) Gas valve opens, allowing propane to flow to the burner. (3) The spark ignites the gas-air mixture at the burner. (4) The flame sensor (flame rectification) detects the flame and signals the board to keep the gas valve open. (5) If no flame is detected within 8-10 seconds, the gas valve closes and the board retries up to 3 times. (6) After 3 failed attempts, the board enters a 30-minute safety lockout. (7) Once the water reaches the thermostat setting (typically 140°F), the thermostat opens, cutting power to the board, which closes the gas valve. When the water cools below the set point, the thermostat closes and the cycle repeats.

Installation Guide

1. Safety first: Turn off propane supply at the tank. Disconnect 12V power at the battery or water heater switch. Also turn off 120V AC if the water heater has an electric mode. Allow the water heater to cool completely.
2. Access the board: Remove the water heater exterior access panel. The ignition board is typically mounted near the burner assembly, visible through the access panel. It may be behind a small plastic cover or mounted directly to the burner housing.
3. Document connections: Take photos of all wiring connections before disconnecting. Note the position of each wire: 12V power (positive/negative), thermostat, gas valve, spark igniter, flame sensor/thermocouple.
4. Disconnect wires: Remove all wire connectors from the old board terminals. Note the position of each wire.
5. Remove old board: Unscrew the 2 mounting screws holding the board to the water heater housing or mounting bracket.
6. Install new board: Mount the new 521099 board in the same position. Secure with the 2 mounting screws.
7. Reconnect wires: Connect all wires to the corresponding terminals on the new board (refer to your photos). Ensure all connections are secure. Double-check the 12V power connections — incorrect wiring can damage the new board.
8. Test operation: Reconnect 12V power (and 120V if applicable). Turn on propane. Turn on the water heater switch inside the RV (select GAS mode if combination unit). Verify the ignition sequence: spark ignites → gas valve opens → burner lights → flame is sensed → continues heating. Check for proper flame (blue with yellow tips). Let the unit run until it reaches temperature and cycles off. If the unit locks out, check all wiring connections, the gas supply, and the electrode gap. Test the electric mode separately if applicable.

Common Symptoms of a Bad Ignition Board

• Water heater won’t ignite on gas mode — no spark or gas
• Spark occurs but gas valve doesn’t open (no flame)
• Flame ignites but won’t stay lit (flame sensing failure)
• Water heater locks out after one ignition attempt (should retry 3 times)
• No spark at the electrode (spark output failure)
• Intermittent gas ignition — works sometimes, not others
• Clicking sound from the board but no ignition
• Burning smell or visible burn marks on the board
• 12V fuse for the water heater blows repeatedly
• Electric mode works but gas mode doesn’t (combination units)
• No hot water on gas mode — burner never ignites

Frequently Asked Questions

Q: What’s the difference between 521099 and 520820?

A: 521099 and 520820 are both water heater ignition boards with the same core functionality. The 521099 is often listed as a replacement or updated version of the 520820. Both boards feature: 12V spark ignition, flame rectification sensing, gas valve control, 3-trial ignition, and 30-minute lockout. The differences may be in the connector type, mounting configuration, or minor component updates. The 521099 is designed to be a direct replacement for the 520820 in most Atwood water heater applications. Always verify the connector type (wire leads vs. edge connector) and mounting hole pattern before installing. If your original board has a part number of 521099, 520820, 520814, 91367, or 31501, this replacement should work. When in doubt, contact our technical team with your water heater model number.

Q: How do I test if my ignition board is bad?

A: To test the ignition board: (1) Verify 12V DC power at the board’s input terminals when the water heater switch is on and the thermostat is closed (water is cool). If no power, the issue is with the switch, thermostat, fuse, or wiring — not the board. (2) If power is present, check for spark at the electrode when the board activates. If no spark, check the spark wire and electrode gap (should be 1/8″). If they’re good, the board’s spark output is bad. (3) Check for 12V output at the gas valve terminals during the ignition phase. If no voltage but spark is present, the board’s gas valve relay is bad. (4) If the burner ignites but won’t stay lit, check the flame sensor. If the sensor is clean and properly positioned, the board’s flame sensing circuit may be bad. (5) If the board doesn’t retry after a failed ignition (locks out after one attempt), the board’s timing circuit is bad. If any of these tests fail and the external components (wiring, electrode, gas valve, flame sensor) are good, the ignition board needs replacement.

Q: Why does my water heater spark but won’t light?

A: If the spark igniter is working but the burner won’t light, the issue is likely with the gas supply or gas valve, not the ignition board. Common causes: (1) No gas supply: Propane tank off, empty, or valve closed. Verify gas reaches other appliances (stove, furnace). (2) Bad gas valve: The gas valve solenoid may be stuck closed or burned out. Listen for a click when the board calls for heat — if no click, the valve may be bad. Test coil resistance (should be 10-30 ohms). (3) Clogged burner or orifice: Spider webs, dust, or debris can clog the gas orifice or burner tube. Spiders are attracted to propane and often build nests. Clean with compressed air or a small wire. (4) Low gas pressure: Faulty regulator or restricted gas line. Test pressure at the water heater inlet (should be 11″ WC). (5) Air in the gas line: If the tank was recently disconnected or refilled, air may be in the line. Purge by turning on gas and letting it flow briefly (with ventilation). (6) Misaligned electrode: The spark may be too far from the gas outlet. Adjust the electrode so the spark jumps at the burner’s gas outlet. If spark is strong and gas is flowing but still won’t light, check the air-gas mixture — a clogged air shutter can prevent proper mixing.

Q: Can I use a furnace ignition board in my water heater?

A: While furnace and water heater ignition boards share similar technology (spark ignition, flame sensing, gas valve control), they are NOT interchangeable in most cases. Important differences: (1) Timing sequences: Furnace boards have pre-purge and post-purge fan control (15-60 seconds), while water heater boards typically don’t have fan control. (2) Fan control outputs: Furnace boards have outputs for the combustion fan and circulation blower (high/low speed), which water heater boards don’t need. (3) Connector configurations: The wire connectors and pinouts are usually different between furnace and water heater boards. (4) Trial ignition times: May differ (furnace: 8 seconds, water heater: 8-10 seconds). (5) Lockout times: May differ. Using a furnace board in a water heater may result in: improper timing, unused fan outputs that could confuse the wiring, connector mismatch, or incorrect gas valve timing. We recommend using the correct board for your specific appliance. For Atwood water heaters, use the 521099, 520820, 91367, or equivalent water heater boards. For Atwood furnaces, use the 520820, 520814, 31501, or equivalent furnace boards. Note: Some part numbers (like 520820) may be used for both furnaces and water heaters in different configurations — always verify by the connector type and wiring, not just the part number.

Related Products

• 91367 RV Water Heater Control Board — Atwood water heater ignition control board
• RV Gas Water Heater Solenoid Valve — 12V gas control valve for water heaters
• 12L Propane RV Water Heater — Complete LPG water heater for RVs

Need help repairing your Atwood water heater ignition system? Contact our technical team with your water heater model number and symptoms. Free shipping and duties included on all orders.