Mobile RV Propane Furnace Repair Across Florida

Why the Furnace Blows Cold Air Even Though the Blower Runs

The most common complaint we hear on furnace calls is that the blower starts, warm air never comes, and then the unit shuts off after a minute or two. This happens because the furnace blower and the ignition system are on separate circuits inside the control board. The blower activates on a thermostat call before the ignition sequence even begins, which is why a cold-air result does not mean the blower is the problem.

In most cases the burner attempted to light and failed, the control board counted the failed attempts, and then locked out the furnace to prevent raw propane from accumulating. The blower may continue running briefly during that lockout period. The underlying cause is almost always the DSI ignitor not producing a strong enough spark, the gas valve not opening due to low propane pressure, or the orifice being partially blocked by corrosion or debris from months of summer storage in Florida's humidity.

What Causes an RV Furnace to Lock Out Without Attempting to Ignite

A lockout that happens before any ignition attempt - meaning no click, no flicker of flame, and no smell of propane - almost always points to the sail switch. The sail switch is a small paddle-and-contact device positioned inside the blower housing. It must physically deflect from the airflow produced by the blower and close its electrical contacts before the control board will allow the gas valve to open. If the paddle is stuck, corroded, or bent out of position, the board receives no signal and the ignition sequence never starts.

The second cause of pre-ignition lockout is a failed control board itself. Atwood and Dometic boards - the two dominant brands in RV furnaces - can develop cracked solder joints or failed relays that prevent the board from reading the sail switch signal or triggering the ignitor even when all the inputs are correct. Testing requires pulling 12-volt DC voltage at the ignitor terminal while the blower is running; no voltage there with a good sail switch signal points directly at the board.

Running the Furnace After a Summer of Storage in Florida

Florida's heat and humidity create specific storage problems for RV furnaces that owners in northern states rarely encounter. The burner orifice - a precisely sized brass fitting that meters propane into the combustion chamber - is exposed to moist air drawn through the combustion intake whenever the furnace sits idle. Over a summer, that moisture can deposit enough oxidation inside the orifice to measurably restrict flow, which causes the furnace to light weakly, trip its high-limit switch, and lock out.

Spider nests in the combustion air intake tube are a related and genuinely dangerous issue. Mud dauber wasps, in particular, build nests inside any dark tube they can access, and the combustion intake on a roadside furnace vent is exactly the right diameter. A blocked intake starves the burner of combustion air, creates incomplete combustion, and can crack the heat exchanger over time. Before running any furnace that has been idle for more than six weeks, the intake and exhaust ports should be visually cleared and the burner tube should be removed and inspected.

How an RV Propane Furnace Differs from a Residential Unit

Homeowners who are used to residential gas furnaces are sometimes surprised to learn that an RV furnace draws no power from the 120-volt AC shore power or generator. The entire unit - blower motor, control board, gas valve solenoid, and ignitor - runs on 12-volt DC from the coach battery bank. This means that a furnace that worked perfectly last season can fail to start if the batteries are depleted, even with full propane tanks and a working thermostat. Low battery voltage is one of the most frequently overlooked causes of intermittent furnace problems in Florida RV parks where owners rely on shore power and neglect battery maintenance.

The combustion isolation is the other key difference. Unlike a residential forced-air system that uses a heat exchanger sitting open in a shared air stream, an RV furnace is a completely sealed combustion appliance. Combustion gases enter through a dedicated external duct and exhaust through a separate external vent. The only air that enters the living space has passed across the outside of the heat exchanger, never through it. This design makes RV furnaces safe in enclosed spaces but also means that any crack in the heat exchanger is immediately a carbon monoxide risk - a cracked exchanger is a replace-the-unit situation, not a repair.

Propane Sharing Between the Furnace, Refrigerator, and Stove

All propane appliances on an RV - the furnace, the absorption refrigerator, the range, the water heater, and any outdoor grill connection - draw from the same propane supply and share the same regulator. The furnace is typically the highest-demand appliance, pulling roughly 35,000 to 40,000 BTU per hour at full fire. Running the furnace with the refrigerator also on propane and a burner lit on the range will not usually cause a problem under normal conditions, but a regulator that is marginally undersized or contaminated with moisture can fail to deliver adequate pressure under combined load. The symptom is weak flame on the stovetop and a furnace that lights briefly and then locks out - both pointing at gas pressure rather than individual appliance failure.

Tank icing is a related Florida-specific issue that surprises owners. When liquid propane vaporizes inside the tank, it absorbs heat. In cold overnight conditions - which do occur in North Florida and Central Florida in December and January - a tank that is less than 20 percent full can ice over at the valve, restricting vapor flow to the point where the furnace cannot maintain ignition. The fix is simple: keep tanks above 30 percent during cold spells and never run two high-demand appliances simultaneously when the tank is low.

How to Reset the Furnace After a Lockout

Most Atwood and Dometic furnaces reset by removing the thermostat call entirely - turning the thermostat down or off - and waiting 30 to 60 seconds for the board to clear its lockout state. Bringing the thermostat back up above room temperature starts a new ignition cycle. If the furnace lights and runs normally on the reset attempt, the fault was likely a one-time event such as a momentary propane pressure drop or a marginal ignitor that succeeded on the second try. If it locks out again on the reset attempt, the fault is repeatable and a technician needs to work through the ignition sequence with a meter to find which component is failing.

One important note: resetting a furnace does not repair it. If a sail switch is borderline, it may pass a few cycles and then fail again when the coach cools down overnight, exactly when you need the heat most. Intermittent furnace problems in Florida are worth diagnosing fully rather than relying on resets, because a furnace that works during the diagnostic appointment and fails at 2am is a much harder problem to solve without a spare part already on the truck.

Blower Motor Failure and the High-Limit Switch It Trips

A weak or failing blower motor produces less airflow than the furnace was designed for. The burner lights normally, but the heat exchanger gets hotter than intended because not enough air is moving across it. The high-limit thermal switch - a safety cutout mounted on the heat exchanger - trips and cuts the gas valve before the exchanger can overheat or crack. The result looks exactly like a control board problem or an ignition problem: the unit lights, runs for 30 to 90 seconds, and then shuts off with the blower continuing. Owners often have the ignitor and sail switch replaced before anyone checks the motor current draw.

Testing the blower motor requires measuring its amperage draw under load and comparing it to the specification on the furnace data plate. A motor drawing above-rated current is dragging, and one drawing significantly below rated current is starting to fail. In Florida's climate, bearing corrosion from humidity is the primary cause of motor degradation - not hours of operation, which is why a 10-year-old furnace used only in winter can have a motor that is still within spec while a unit stored in a humid coastal environment for three years may not. Replacing the motor rather than the board is the correct fix, and it is less expensive.

Furnace Repair Pricing

The following ranges cover parts and labor for the most common furnace repairs performed at the coach. All service begins with a diagnostic visit; pricing below is for the repair itself once the fault is confirmed.

Common Questions About RV Furnace Repair

Sources

• Atwood RV furnace documentation - Ignition sequence, sail switch specs, and lockout reset procedures.
• Dometic RV heating products - Propane furnace models, burner specifications, and control board diagnostics.