RV Furnace Fuse Location and How to Find It

The RV furnace fuse location is a common question for owners diagnosing a non-working furnace. This article explains where fuses and breakers are typically found, differences between furnace models, step-by-step troubleshooting, fuse specifications, and safe replacement practices to get heat back quickly. Knowing where the fuse is and how to check it can prevent unnecessary service calls and help avoid electrical hazards.

Furnace Brand/Type	Common Fuse Location	Fuse Type
Suburban	Access panel near blower or inside furnace control box	Inline blade fuse or glass fuse 3–20A
Atwood/Marathon	Near furnace control board or external inline holder	Automotive blade or cylindrical fuse 3–15A
Dometic	Control panel, furnace cabinet, or fuse block	Slow-blow or blade 5–20A

How RV Furnaces Are Fused

RV furnaces rely on a low-voltage 12V DC circuit for controls, blower motors, and ignition. Manufacturers protect these circuits using fuses located either inside the furnace cabinet, in an external inline holder, or at a centralized fuse/breaker panel. Some models also use thermal fuses or circuit breakers for motor protection.

Common Fuse Locations By Furnace Brand

Suburban Furnaces

Suburban furnaces frequently place the fuse on or near the control board inside the furnace cabinet behind the lower access panel. Inline fuses may be clipped to a harness near the blower. Check the area around the blower motor and the primary circuit board.

Atwood / Marathon Furnaces

Atwood (also sold as Marathon) models often use an inline fuse holder on the 12V power lead, sometimes located outside the furnace cabinet along the wiring harness. A small glass or blade fuse near the control board is common on older models.

Dometic Furnaces

Dometic furnaces can have fuses in the control panel, the furnace housing, or at a dedicated 12V fuse block. Newer units may include a labeled fuse on the chassis or a blade fuse in an external fuse box near other DC circuits.

How To Locate The Fuse Step-By-Step

1. Turn Off Power: Disconnect 12V power at the battery or main DC panel to prevent shorts.
2. Access Furnace: Remove exterior access door or interior lower panel to expose the furnace cabinet.
3. Inspect Control Board Area: Look for a small fuse holder, glass fuse, or blade fuse near the circuit board or wiring harness.
4. Follow The Power Wire: Trace the red 12V lead from the furnace to find inline fuse holders or connectors.
5. Check Central Fuse/Battery Panel: Some RVs place furnace fuses on the main DC fuse block or a labeled mini-breaker.
6. Consult The Manual: Manufacturer manuals and wiring diagrams show exact fuse locations for the specific model.

Identifying Fuse Types And Ratings

Common fuse types for RV furnaces include automotive blade fuses (ATO/ATC), cylindrical glass fuses, and small slow-blow fuses. Typical ratings range from 3A to 20A, with blower and control circuits most often protected by 3–10A fuses. Always match the original fuse type and amperage when replacing.

Troubleshooting When Furnace Won’t Start

If the furnace fails to run, check fuses first, then proceed through a systematic troubleshooting flow: verify 12V supply at the furnace, test the thermostat or control board, confirm the high-limit/thermal cutoff isn’t tripped, and inspect ignition components and the blower motor. Fuses blowing repeatedly indicate a deeper short or motor fault requiring repair.

Quick Diagnostic Checklist

• Confirm 12V at battery and DC panel.
• Inspect fuse visually for a broken filament or discoloration.
• Test fuse with a multimeter for continuity.
• Check for loose, corroded, or damaged wiring at terminals.
• Listen for blower motor hum or attempt to run furnace briefly (only after confirming fuse condition).

How To Safely Replace A Fuse

Always disconnect the 12V source before replacing a fuse. Use a fuse with the exact amperage and type specified by the manufacturer. Replace blown fuses with new ones and avoid temporary solutions like foil or mismatched ratings, which can cause wiring damage and fire.

Tools And Supplies Needed

• Multimeter for continuity and 12V checks.
• Replacement fuses (correct type and amperage).
• Small screwdrivers or nut drivers to remove furnace panels.
• Needle-nose pliers for inline holders and connectors.

When A Fuse Keeps Blowing

Recurring fuse failure signals an underlying electrical problem. Common causes include a failing blower motor drawing excessive current, shorted wiring or pinched harness, bad control board components, or incorrect fuse rating previously installed. Diagnose with a multimeter and inspect windings on the motor and continuity across suspect circuits.

Steps To Diagnose Repeated Blows

1. Verify correct fuse rating and install a new fuse.
2. Measure current draw of blower motor; compare to spec.
3. Isolate circuits by disconnecting devices to find which one trips the fuse.
4. Inspect and repair damaged insulation or connectors.
5. Replace defective components rather than using higher-rated fuses.

Thermal Fuses And High-Limit Switches

In addition to standard fuses, furnaces employ thermal fuses and high-limit switches that protect against overheating. These components are typically mounted on the heat exchanger or control board and may be non-resettable. Testing requires continuity checks and replacement when open. Do not bypass thermal devices.

Fuse Versus Circuit Breaker: What RVs Use

RVs use both fuses and circuit breakers. Many modern RVs use blade fuses for individual circuits and auto-resetting or manual DC circuit breakers for higher-load devices. Furnace circuits are usually fused to protect wiring rather than placed on a breaker, though some designs use a breaker at the DC panel.

Tips For Faster Identification

• Keep the RV owner’s manual and a wiring diagram in the glovebox for model-specific guidance.
• Label furnace and DC panel fuses after identifying them to save time later.
• Carry spare fuses of the correct type and a compact multimeter when traveling.
• Document fuse locations with photos for future reference.

Safety Precautions

Always remove 12V power before accessing the furnace wiring. Use insulated tools and wear eye protection when working in confined spaces. If a repair involves gas components, shut off the propane and consult a certified RV technician. When unsure, seek professional service.

When To Call A Professional

Contact a certified RV technician when fuses blow repeatedly, wiring damage or corrosion is extensive, the blower motor fails, gas ignition is unreliable, or when detection of a fault requires complex testing. Professionals can perform load testing, control board diagnostics, and safe gas system checks.

Frequently Asked Questions

How Can The Fuse Be Tested Without Removal?

A multimeter set to continuity or resistance can test the fuse in-place if accessible. For blade fuses, probe both terminals; for inline glass fuses, remove one end for a reliable reading. No continuity means the fuse is open.

Can The Furnace Run On Shore Power If 12V Fuse Is Blown?

No. Most RV furnaces require 12V DC for controls and blowers; shore power alone will not operate the 12V circuitry unless an onboard converter provides DC and the correct fuse is intact.

Is It Safe To Replace A Fuse With A Higher Amp Rating?

No. Installing a higher-rated fuse defeats the protective purpose and can cause wiring to overheat and catch fire. Always use the manufacturer-specified fuse rating.

Additional Resources

Owner manuals, manufacturer wiring diagrams, and RV electrical guides are valuable resources. Online forums, manufacturer tech sheets, and service manuals provide model-specific fuse locations and electrical schematics for deeper diagnostics.

By following these guidelines, locating an RV furnace fuse and performing safe, correct replacements becomes straightforward. Proper diagnosis prevents repeated failures and keeps the RV heating system reliable.