Propane safety — read this first.
- If you smell gas (a rotten-egg odor) inside or around the RV: turn the propane off at the tank if you can do so safely, do not light anything, do not flip electrical switches, get everyone out, and call for help from outside the rig.
- Never open, adjust, or disconnect a gas valve, gas line, fitting, or burner orifice. Nothing in this guide requires touching the gas supply beyond checking that the tank valve is open. Anything involving gas valves or lines is a job for a qualified technician — full stop.
- Keep a working carbon monoxide alarm in the rig, and if it sounds, treat it the same way: out first, questions later. A furnace with a combustion problem is not something to “test one more time.”
- Do not bypass any safety switch — limit switch, sail switch, or ignition control — to make the furnace run. If a safety switch is stopping the furnace, it is doing its job.
A dead furnace usually announces itself on the first cold night of the season — often the first foothill trip after months in storage around Auburn, Placerville, or Grass Valley. The good news: many “furnace failures” are really supply problems — no propane reaching the unit, not enough battery voltage, or a thermostat not actually calling for heat. Work through the checks below in order. None involve opening the furnace, removing panels, or touching wiring or gas components.
Step 1: Name the exact symptom
- Nothing happens at all — no blower, no sound. Points first at the thermostat, a fuse or switch, or very low battery power.
- Blower runs, but the air never gets warm, then the blower stops. The furnace tried to light and failed its ignition sequence, or never got gas. This is the most common pattern.
- Blower runs and warm air starts, then it shuts down after a few minutes. Can be an overheating pattern from restricted airflow, or a flame-sensing problem.
- It works on shore power but not on battery alone. Almost always a battery or charging problem — see Step 4.
- It short-cycles — frequent short runs without reaching temperature. Often thermostat placement, airflow, or a control issue.
A healthy start-up has a recognizable sequence: blower first, then clicking as the igniter tries, then a whoosh as the burner lights, and warm air follows. Noting which step yours reaches tells a technician a great deal.
Step 2: Check the thermostat
Confirm the thermostat is set to Heat (not Cool or Fan), the fan is on Auto, and the set temperature is several degrees above room temperature. If it uses batteries, replace them — a weak thermostat battery causes exactly this kind of dead or erratic behavior. On rigs where the thermostat also controls the air conditioner, confirm you are adjusting the right zone. Give each change a few minutes; furnaces have built-in delays and lockouts after a failed ignition attempt, and turning the thermostat off and back on is what resets many of them.
Step 3: Confirm the propane supply — from outside the furnace
The furnace cannot light without gas, and “the tank felt heavy last spring” is not a gauge. Check the level by the gauge if you have one, and confirm the tank's service valve is open. A simple supply test is to light a stovetop burner (normal cooking use): if it lights and holds a steady flame, propane is reaching the appliances. If the stove will not light either, the problem is the supply, not the furnace — and anything beyond confirming the tank valve is open belongs to a technician. Open a tank valve slowly, by the way: opening it fast can trip the excess-flow safety valve and starve every appliance, which looks exactly like an empty tank.
Step 4: Check your 12-volt power
The furnace runs on 12-volt battery power even though it burns propane — the blower, igniter, and control board are all electric. A weak battery is one of the most overlooked causes: the blower may spin too slowly to prove airflow to the sail switch, so the burner never lights — or the furnace works plugged in and fails the moment you unplug. Check that the battery disconnect switch is on, and look at the fuse panel for a blown furnace fuse. Replacing a fuse with one of the same rating is fine; if it blows again, stop and call a tech rather than fitting a larger one. If your lights dim noticeably when the blower starts, say so when you call — that points straight at the battery.
Step 5: Check airflow and the outside vents
Inside, make sure the warm-air registers are open and not blocked by rugs, storage, or pet beds, and that the return-air path is clear — a furnace starved for return air overheats and shuts down on its limit switch. Outside, look at the intake and exhaust vents on the sidewall: after storage, mud daubers and insects love to build in them, and a blocked exhaust will stop a furnace cold. Clear only loose debris you can reach from outside. Do not push anything into the vent, remove the vent assembly, or open the furnace's access panel to dig deeper — internal cleaning is technician work.
Stop and call a tech if you notice any of these
- Any smell of gas at any point, or a carbon monoxide alarm sounding.
- The furnace tries to light repeatedly with a loud bang or delayed ignition.
- Soot around the outside vent, a yellow or lazy-looking flame at another appliance, or scorch marks anywhere.
- The blower squeals, grinds, or will not spin.
- It still will not light after the thermostat, propane, battery, fuse, and airflow checks above — the next steps involve the gas valve, igniter, control board, and safety switches, and all of them are inside the unit.
- The next step would require opening the furnace. That is the line this guide does not cross, and neither should you.
What to tell the technician
Have ready: the furnace brand and model from the label inside the rig or in your manuals, which step of the start-up sequence it reaches (blower, clicks, heat, shutdown), whether the stove lights normally, whether it behaves differently on shore power versus battery, the fuse status, and where the RV is parked. That narrows the diagnosis before the tech arrives and makes a first-trip fix more likely. Our furnace and water heater repair page covers what a mobile tech tests on site, and our guide to mobile RV repair costs in Northern California explains how the bill is built before you approve anything.
More owner guides
- Winterizing your RV in Northern California — the cold-weather checklist foothill rigs need, furnace included.
- RV refrigerator not cooling: troubleshooting guide — the same work-the-list approach for Norcold and Dometic fridges.
- RV slide-out maintenance — seals, tracks, and the checks that prevent a stuck slide.
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Disclosure: NorCal RV Repair is an independent referral service, not a repair shop. We connect RV owners in Northern California with local independent mobile RV technicians. We do not perform repairs ourselves, and pricing and warranties are provided by the independent technician who does your work. This article is general educational information about common troubleshooting practice, not a substitute for your RV and appliance manufacturers' instructions — always follow the manuals for your specific rig, and do not attempt any repair involving propane gas valves or lines, electrical components, or the furnace's internal components.