RV Furnace Flame Sensor: How It Works, Troubleshooting, Testing, and Replacement

The RV furnace flame sensor is a small but critical component that ensures safe, reliable operation of an RV’s heating system by detecting the presence of a flame and preventing gas flow if ignition fails. This guide covers how the flame sensor works, common failure symptoms, step-by-step testing, replacement tips, maintenance best practices, and cost considerations for American RV owners.

Item	Quick Facts
Primary Function	Detects flame to allow continuous gas flow
Common Failures	Dirty sensor, broken wiring, bent sensor rod
Tools Needed	Multimeter, screwdriver, sandpaper, replacement sensor
Typical Cost	$15–$60 for parts; $80–$200 labor if serviced

What Is An RV Furnace Flame Sensor And Why It Matters

An RV furnace flame sensor is a metal rod or probe located in the combustion chamber near the burner flame. It detects the presence of heat or ionized flame and sends a signal to the furnace control board to continue supplying gas. If it does not sense a flame, the control board shuts off gas to prevent dangerous unburned propane accumulation. Reliable flame sensing is essential for safety, efficient heating, and preventing component damage.

How The RV Furnace Flame Sensor Works

The sensor operates using one of two common methods: thermocouple/thermopile effect or flame rectification. In thermocouple/thermopile systems, two dissimilar metals generate a small voltage when heated by the flame. In flame rectification systems, the control board applies an AC signal and detects DC current flow through the ionized flame to prove ignition. Most modern RV furnaces use flame rectification, while older units may use thermocouples.

Common Symptoms Of A Failing Flame Sensor

• Short Cycling: Furnace lights briefly then shuts off repeatedly.
• No Heat After Ignition Clicks: Furnace attempts to ignite but gas valve closes before steady flame forms.
• Error Codes Or Lockouts: Control board displays fault codes related to flame detection.
• Intermittent Operation: Heater works sometimes and fails at other times without an obvious cause.
• Visible Corrosion Or Damage: Sensor rod bent, burned, or covered with soot.

Diagnosing The Problem: Preliminary Checks

Before assuming the flame sensor is defective, technicians recommend checking basic items that commonly cause similar symptoms. Verify propane supply, battery voltage, thermostat settings, and vents/ducts. Low battery voltage or blocked venting can cause ignition failures and mimic sensor problems. Ensure the furnace has clean air intake and exhaust paths and that the thermostat calls for heat.

How To Test An RV Furnace Flame Sensor

Testing should be performed safely with propane off when accessing electrical connections, and with the furnace powered and venting properly during live flame tests. If uncomfortable with live testing, seek professional service.

Visual Inspection

Inspect the sensor rod for soot, corrosion, breaks, or bending. Clean light deposits with fine-grit sandpaper or steel wool and reinstall for a quick check. Damaged or melted sensors must be replaced.

Continuity And Resistance Test

Using a multimeter, check for continuity across the sensor wiring if applicable. Thermocouples typically show very low resistance and produce millivolts when heated. Flame rectification sensors do not produce significant DC voltage themselves; instead, testing focuses on current flow to the control board during operation.

Live Flame Rectification Test

With the furnace attempting ignition, set the multimeter to measure microamperes or the furnace control board may report a measured flame current. Some control boards require a minimum microamp reading (commonly 1–10 µA) to register a flame. Consult the furnace manual for the exact threshold. If the measured current is below the threshold despite a visible flame, the sensor or wiring likely needs replacement.

Thermocouple Voltage Test

For thermocouple-style sensors, heat the tip with an open flame and measure millivolt output with a multimeter. Typical thermocouple outputs range from 20–30 mV when hot, but consult equipment specifications. Absence of expected millivolts indicates failure.

Replacing An RV Furnace Flame Sensor: Step-By-Step

Replacement is often a straightforward DIY task for someone comfortable with basic tools. Required tools include screwdrivers, a socket set, a multimeter, needle-nose pliers, and replacement sensor specified for the furnace model.

1. Turn off propane supply and disconnect batteries or power to the furnace to prevent accidental ignition.
2. Remove furnace access panels per the manufacturer’s instructions to expose the burner assembly and sensor.
3. Document or photograph the sensor wiring and mounting orientation before removal to ensure correct reassembly.
4. Disconnect sensor wiring harness or terminal, and remove mounting fastener(s) that hold the sensor in place.
5. Install the new sensor in the exact position and orientation as the original; sensors must sit at the correct height and distance from the burner for reliable sensing.
6. Reconnect wiring, reattach access panels, restore propane and power, and perform an ignition cycle to verify proper operation.

Tip: Only use OEM or compatible sensors specified in the furnace manual. Substituting different lengths or types can result in poor sensing and safety issues.

Maintenance Tips To Extend Sensor Life

• Regularly clean the sensor tip during annual furnace servicing to remove soot and carbon buildup.
• Keep the combustion chamber and burner ports clean for consistent flame shape and heat distribution.
• Inspect wiring and connections for corrosion or loose terminals during routine checks.
• Replace the sensor proactively if it shows physical wear rather than waiting for failure.

Cost, Parts, And Sourcing

Replacement flame sensors for RV furnaces commonly cost between $15 and $60 for parts depending on brand and type. Labor at an RV service center ranges from about $80 to $200 for diagnostic and replacement work. Prices vary by region and complexity. Genuine OEM parts from furnace manufacturers such as Suburban, Atwood, Dometic, or others are recommended. Online RV parts retailers and authorized dealers are primary sources.

Common Models And Compatibility Notes

Different RV furnace models use different sensor designs and connectors. Suburban and Atwood (now part of Dometic) have long-used specific sensor lengths and plug types. When ordering, match the part number or provide furnace model and serial information. Do not rely solely on visual similarity—verify electrical and mechanical compatibility.

Safety Precautions And Best Practices

Work on an RV furnace only when comfortable with gas and electrical systems. Always shut off propane and disconnect battery power before disassembling the burner area. After replacement, observe at least two successful ignition cycles and inspect for gas odors. If any odor of propane is present, shut off supply, ventilate, and contact a qualified technician. Flame sensors are safety devices; improper installation or incorrect parts can create hazardous conditions.

When To Call A Professional

Contact an RV technician if troubleshooting steps do not resolve the issue, if wiring or control board faults are suspected, or if the furnace exhibits persistent electrical or gas valve issues. Professionals have diagnostic equipment to test flame rectification currents and control board behavior and can safely handle gas-related repairs and regulatory compliance.

Useful Resources And Further Reading

• Manufacturer Support Pages (Dometic/Suburban/Atwood)
• RVing Know-How Troubleshooting Guides
• RV Repair Club: Furnace Maintenance

Quick Troubleshooting Checklist

Problem	Likely Cause	Quick Action
Furnace Lights Then Shuts Off	Dirty sensor, weak battery, low propane	Clean sensor tip, check battery voltage, verify propane
No Ignition With Clicking	Faulty igniter, wiring, sensor	Inspect igniter, test sensor, call tech if wiring damaged
Intermittent Heat	Loose connections or aging sensor	Tighten connectors, replace sensor

Final Practical Tips For RV Owners

Include a simple multimeter and a spare flame sensor in the RV toolkit for remote troubleshooting. Schedule an annual furnace inspection before the cold season. Track furnace model, part numbers, and service history to speed repairs and part ordering. Proactive maintenance reduces the chance of being left without heat during travel.