For informational purposes only. Information may not be complete or accurate. Always verify before use. For complex RV repairs, consult a qualified RV technician or mechanic. See our Terms of Service.

Suburban RV Furnace Won't Work on Shore Power - Complete Fix Guide

By RV Repair Question • Updated January 12, 2026

Propane Medium 2-3 hours 8 views

Mike R. RV Owner

Suburban furnace works on battery but not shore power - voltage issue? Read full question

Suburban furnace works on battery but not shore power - voltage issue?

So I'm dealing with this weird issue on my 2016 Heartland Bighorn where the Suburban furnace acts totally different depending on the power source. When I'm running off battery power, the thing works like a champ - fires up, heats great, cycles on and off perfectly.

But the second I plug into shore power? It's like the furnace forgets how to do its job. It'll run for about 4 minutes, never actually produce heat, then shut off and lock out until I reset everything. The only way to get it working again is to disconnect shore power and cycle the battery.

I'm wondering if this is some kind of converter problem? Like maybe it's sending the wrong voltage to the furnace control board when on shore power? Has anyone run into this before and know what voltage levels I should be checking?

Dear Mike R.,

Quick Answer

When a Suburban RV furnace only works on battery power but fails to heat on shore power, the issue is typically a converter providing incorrect voltage (13.8V+ instead of 12V) to the control board. The solution involves checking voltage levels and potentially adjusting or replacing the converter.

Tools & Parts Needed

digital multimeter screwdrivers wire strippers electrical tape

Find these on Amazon: Digital Multimeter , DC Voltage Reducer , RV Wire Strippers

The Problem

Your Suburban furnace issue is a classic symptom of converter voltage problems. RV furnace control boards are designed to operate on 12V DC, but many converters output 13.8V or higher when plugged into shore power.

What's Going Wrong

This higher voltage can cause the control board to malfunction, preventing proper ignition sequencing even though the furnace appears to run.

Progressive Dynamics and WFCO converters are notorious for this issue. These units output charging voltage (13.8V+) continuously when on shore power, which may cause issues with some furnace control boards (check your specific model's voltage specifications). Older furnaces were more tolerant of voltage variations.

The 4+ minute runtime you're experiencing may indicate the furnace is cycling through multiple startup attempts, as typical Suburban furnace ignition lockout occurs within 15-30 seconds of ignition failure.

The Solution

SAFETY WARNING: Turn off the gas supply to the furnace before performing any electrical troubleshooting.

You'll need:

Digital multimeter
Basic hand tools (screwdrivers)
Wire strippers (if modifications needed)
Electrical tape
Voltage reducer or new converter (potentially)

Follow these steps:

Measure voltage at the furnace: Turn off the furnace, then with shore power connected, use your multimeter to check the DC voltage at the furnace control board connections. You'll likely find 13.8V to 14.4V instead of the required 12V.
Test on battery power: Disconnect shore power and measure the same connections running on battery only. This should read closer to 12.6V-12.8V, which explains why it works properly.
Check converter output: Locate your RV's converter/charger and measure its 12V output terminals. Most modern converters output 13.8V-14.4V for battery charging, which is too high for sensitive electronics.
Verify the pattern: Reconnect shore power and confirm the voltage increases. This confirms your converter is the culprit.

Know When to Call for Backup

Contact a certified RV technician if:

You're uncomfortable working with 12V electrical systems
Voltage readings don't match this diagnosis
The furnace still won't work after voltage correction
You discover damaged wiring or connections
Gas odors persist or you suspect gas leaks

Ongoing Maintenance

Many RV manufacturers are now aware of this compatibility issue. When replacing converters, choose models with "smart" or "multi-stage" charging that drop to float voltage (13.2V-13.4V) after initial charging. This prevents the high voltage condition that causes furnace problems.

Regular voltage monitoring of your 12V system can help identify converter issues before they affect other sensitive electronics like water heater control boards or LED lighting.

This article is for informational purposes only and may contain errors. Always verify technical specifications and safety procedures with your equipment manufacturer's documentation or consult a qualified professional before performing repairs. See our terms.

Spot something wrong?

Help us improve this article by flagging technical issues or inaccuracies.

Was this guide helpful?

Need More Help?

Try our free RV calculators and tools to help diagnose and plan your repairs.

Browse RV Tools

Weight calculator, electrical planner, propane estimator & more

Tags: #suburban-furnace #converter-problems #shore-power #voltage-issues #furnace-wont-heat