Suburban ST-60 Water Heater Control Board 521339

The Suburban 521339 Control Board is the replacement electronic control board for the Suburban ST-60 on-demand RV water heater. The board manages the heater’s operating and ignition sequence and is a key component when an ST-60 fails to start, ignite, or operate properly.

The 521339 replaces Suburban part number 233666 and is supplied as a kit with the outer protective case.

Models It Fits

The Suburban 521339 is designed specifically for:

• Suburban ST-60

• ST-60 on-demand / tankless RV water heaters

This board is not interchangeable with the ST-42 control board. The ST-42 uses Suburban 521338, while the ST-60 uses 521339.

Replaces Part Number

• 233666

Suburban parts documentation identifies the 521339 as the replacement control board for the original 233666 used in the ST-60.

What the 521339 Control Board Does

The control board coordinates the electronic operation of the ST-60 tankless water heater, including the ignition and burner operating sequence.

The ST-60 is a 60,000 BTU on-demand water heater with electronic safety systems including flame-out protection, automatic fan monitoring, freeze protection, scald protection, and voltage protection.

Signs & Symptoms of a Failed Control Board

A faulty control board may cause symptoms such as:

• Water heater will not start

• Burner will not ignite

• Heater attempts ignition but fails to complete the cycle

• Intermittent operation

• Burner shuts down unexpectedly

• Ignition or gas valve components are not being commanded properly

• Other components test correctly but the heater remains inoperative

Because several other ST-60 components can cause similar symptoms, verify the propane supply, 12V power, wiring, grounds, sensors, ignition components, and airflow system before replacing the control board.

Estimated Install Time

Approximately 20–45 minutes, depending on water heater access and wiring location.

Tools Required

• Phillips screwdriver

• Nut driver or socket set

• Multimeter

• Basic electrical hand tools

Potential Issues

Disconnect electrical power and LP gas before servicing the water heater.

Before removing the original board, take a photo of the wiring and connector locations. This can make transferring the connections to the new board much easier and help prevent incorrect installation.

If replacing the board does not correct the problem, additional diagnosis may be needed. Low voltage, poor grounds, failed sensors, ignition problems, airflow issues, propane supply problems, or damaged wiring can all produce symptoms similar to a failed control board.

Product Specifications

Manufacturer: Suburban / Airxcel
Part Number: 521339
Replaces: 233666
Part Type: Water Heater Control Board
Application: Suburban ST-60 On-Demand Water Heater
Includes: Control Board and Outer Protective Case

Important: The 521339 fits the ST-60 only. For a Suburban ST-42, use Suburban control board 521338.