Suburban SDN2U Water Heater Won't Stay Lit: Thermocouple Position Fix

What's Going On

Your 2025 Jayco's Suburban SDN2U left burner issue is indeed a known problem that you're right to be frustrated about. The thermocouple on that burner is likely either positioned incorrectly from the factory or has shifted slightly, preventing it from getting enough heat signal to keep the gas valve open. Since you've confirmed the thermocouple appears to be in the right position compared to the working right burner, this is most likely a factory calibration or positioning issue that Suburban has acknowledged but hasn't widely publicized the fix for.

The "adjustment" that dealers have been told about typically involves either repositioning the thermocouple closer to the flame or replacing the entire burner assembly if the thermocouple mounting is defective. Since this is a 2025 unit, you're definitely still under warranty, and this should be covered as a manufacturing defect.

Why This Happens

Suburban added thermocouples to the SDN2U burners as a safety feature to automatically shut off gas flow if the flame goes out. However, the manufacturing tolerances on the thermocouple positioning have been inconsistent, particularly on the left burner assembly. The thermocouple needs to be positioned so its tip sits directly in the flame path and receives consistent heat to the temperature specified by the manufacturer to generate enough voltage to keep the gas valve open.

Even a millimeter or two of misalignment can cause the thermocouple to not get enough heat signal, especially on the smaller left burner where the flame pattern is more compact. Some units left the factory with the thermocouple positioned too far from the burner ports, while others have thermocouples that weren't properly secured and have shifted over time during shipping and handling.

The issue is more common on the left burner because it's typically the smaller of the two burners, producing a more concentrated flame pattern that requires more precise thermocouple positioning. Additionally, the left burner assembly may have different manufacturing specifications that haven't been properly coordinated with the thermocouple mounting hardware.

Getting Ready

SAFETY WARNING: Turn off propane supply at the tank, disconnect electrical power to the unit, and allow the stove to cool completely before beginning any work. Turn off the main propane tank valve and wait for any residual gas in the lines to dissipate. Work in a well-ventilated area with proper gas detection equipment available and never use open flames or sparks near gas appliances during service.

Before attempting any repairs, you'll need a Phillips head screwdriver, needle-nose pliers, and a small adjustable wrench. Have your phone ready to document the current thermocouple position with photos before making any changes, as this will help if you need to involve warranty service later.

Remove the burner grate and drip pan to access the burner assembly clearly. You should be able to see the small thermocouple probe extending toward where the flame would be. Compare its position carefully to the working right burner - note not just the distance from the burner ports, but also the angle and height of the thermocouple tip.

Check that the thermocouple connections are tight at the control valve underneath the cooktop. Loose connections can cause the same symptoms as poor positioning. Also verify that the burner ports are clean and free of debris that might affect flame pattern, though this is less likely on such a new unit.

Walking Through the Fix

The most common successful fix involves carefully repositioning the thermocouple closer to the flame. With the burner assembly exposed, locate the small bracket or clip holding the thermocouple in position. This is usually secured with a small screw or metal clip that can be loosened to allow repositioning.

After identifying the specific mounting bracket type and loosening the retaining hardware (hand-tighten plus 1/4 turn unless you have access to manufacturer torque specifications), adjust the thermocouple so its tip extends further into the flame path, positioning it similar to the working burner but accounting for the different flame pattern of the smaller left burner. The tip should be angled so it will sit directly in the hottest part of the flame, approximately 1/2 to 3/4 inch from the burner ports (exact positioning may vary - consult manufacturer documentation if available).

If repositioning doesn't work, the issue may be a defective thermocouple or gas valve, which requires professional diagnosis with specialized equipment to test thermocouple voltage output and gas valve operation. In this case, you'll need to contact Suburban directly through their technical support line at 423-775-2131, as they have issued revised installation instructions for dealers. Ask about any available service bulletins regarding thermocouple adjustment procedures for your specific model.

Test your adjustment by lighting the burner and observing whether it stays lit for several minutes. The flame should burn steadily around the thermocouple tip without flickering away from it. WARNING: Perform thorough leak testing on all gas connections that were disturbed during the repair using approved gas leak detection solution - improper thermocouple adjustment or loose connections can create serious gas leak hazards. If you smell gas at any point, shut off the propane immediately and seek professional service. If it stays lit consistently and passes leak testing, reassemble the cooktop components and test normal operation.

Beyond DIY Territory

Since your 2025 Jayco is under warranty, I'd strongly recommend documenting this issue with photos and contacting Jayco's customer service at 574-825-4400 before doing extensive troubleshooting yourself. They can contact Suburban directly and may authorize warranty repair at a closer dealer or provide a mobile service option.

If the thermocouple repositioning doesn't solve the problem, you're likely looking at a defective gas valve or control assembly, which definitely requires professional service. These components are under pressure and involve gas connections that must be properly torqued and leak-tested after service.

The Jayco forums you mentioned are reporting that some dealers have received updated burner assemblies with revised thermocouple mounting hardware. You'll need the correct part for your model (verify with dealer), and the revised version should solve this issue permanently. Given that this is a widespread problem on new units, push for warranty coverage rather than paying out of pocket for what appears to be a design/manufacturing issue.