An RV's appliances each run on one of three supplies: the 12-volt battery, 120-volt shore power, or propane. A fresh water system feeds the ones that use water. Knowing which supply an appliance draws on tells you where to look first when it stops working.
RV Systems Explained: Air Conditioning, Heat, Hot Water and Propane
On this page (5)
What runs on 12 volts, 120 volts and propane
Most coaches split the work like this, as the owner's manuals describe it.
| Supply | What it usually runs |
|---|---|
| 12-volt battery | Lights, water pump, furnace blower, appliance control boards |
| 120-volt shore power | Air conditioner, microwave, wall outlets, battery charging |
| Propane | Furnace, water heater, cooktop, absorption refrigerator |
Layouts vary by floor plan and model year, so the appliance list for your own coach is in the manual that came with it. The supplies themselves, including the converter and inverter that move power between them, are covered on the hub for RV batteries and power explained.
Tip: Most failures start with the supply, not the appliance. Before you open anything, confirm the tank valve is open, the breaker is on, the battery disconnect is closed and the thermostat is calling for heat or cooling.
Which page covers each appliance
Cooling, heat and controls:
- RV air conditioners explained: what rooftop units run on and how capacity is rated.
- Soft starts for RV air conditioners: what one changes at startup.
- RV air conditioner maintenance: filters, coils and the roof gasket.
- RV thermostats explained: how the thermostat talks to the furnace and the AC.
Hot water, water supply and propane:
- RV water heaters explained: propane, electric and both.
- Tankless RV water heaters: how on-demand units differ.
- RV water heater anode rod: what it protects and when it gets replaced.
- RV water pumps explained: how the pump is switched and plumbed.
- RV propane tanks: sizes, valves and filling.
- The RV propane regulator: what it does and where it sits in the system.
Where do I start when something stops working?
Each appliance has its own fault page, which follows the checks in the makers' manuals in their order. Go to the one that matches the symptom:
- RV air conditioner not cooling
- RV furnace not working
- RV water heater not working
- RV water pump problems
- RV refrigerator not cooling
Tip: The furnace, the water heater and an absorption refrigerator all need 12-volt power for their control boards even while they burn propane. A flat battery makes all three look like a propane fault.
Propane leaks, alarms and 120-volt work
Propane is sold with an odorant added, so a leak smells like rotten eggs. The Propane Education & Research Council advises leaving the vehicle at once if you smell gas: put out any flame, leave switches alone, shut the tank valve if you can reach it safely, open the door and have the system checked before using it again.
The propane alarm is mounted low because propane is heavier than air; the carbon monoxide alarm sits higher. Replace both by the date printed on the housing. A sounding alarm is covered on RV propane alarm going off. Work behind the 120-volt panel, and any repair to a propane line or regulator, is a job for a licensed RV technician.
Water, seasons and the rest of the coach
Tanks, plumbing, the toilet and waste handling are indexed separately on the RV water system explained. Draining those lines before a freeze is covered in how to winterize an RV, and the roof, seals, awning and tires sit under RV exterior care by season.
All guides in this section
- How to Winterize an RV: The Antifreeze and Blow-Out Methods, Step by Step
How to winterize an RV step by step: draining, bypassing the water heater, pumping RV antifreeze or blowing out the lines, and the traps and toilet.
- RV Air Conditioner Maintenance: Filters, Coils, Drains and the Yearly Checks
How to maintain an RV air conditioner: filters, coils and drain openings, the shroud and the roof gasket, and which jobs to leave to a service tech.
- RV Air Conditioner Not Cooling: What to Check, in Order
Why an RV air conditioner runs but does not cool, or will not start, and the checks in order from the makers' manuals, before you call a technician.
- RV Air Conditioners Explained: Rooftop, Ducted, 12 V and Portable, and BTU Sizing
How RV air conditioners work: rooftop non-ducted and ducted, low profile, heat pump, 12 V and portable units, BTU sizes, and what replacing one involves.
- RV Furnace Not Working: What to Check When the Propane Heat Fails
Why an RV propane furnace will not light, blows cold air or shuts off, the checks in order from Suburban and Dometic manuals, and how much propane it uses.
- RV Propane Alarm Going Off: What to Do, the Causes and When to Replace It
What to do when the RV propane alarm sounds, the real and false causes the makers list, low-battery chirps, the reset, and the detector's end-of-life date.
- RV Propane Tanks: Sizes, Filling vs Exchange and the Date That Matters
RV propane tank sizes, DOT cylinders vs ASME tanks, filling vs exchange, the requalification date stamped on the collar, and the safety rules.
- RV Refrigerator Not Cooling: Checks for Norcold and Dometic Fridges
Why an RV fridge is not cooling on gas, electric or both, the checks in order from the Norcold and Dometic manuals, the reset, and when to call a tech.
- RV Thermostats Explained: Types, Why a House Thermostat Will Not Do, Replacing One
How an RV thermostat runs the air conditioner and furnace, analog vs digital vs zoned, why a home thermostat is not a swap, and replacing one with a match.
- RV Water Heater Anode Rod: When to Check It, Replacing It and Flushing the Tank
Which RV water heaters need an anode rod, when to check and replace it, how to drain and flush the tank, and why Atwood heaters use a plain drain plug.
- RV Water Heater Not Working: Gas, Electric and Tankless Checks
Why an RV water heater gives no hot water on gas, on electric or both, and the checks in order from the makers' manuals, including the reset.
- RV Water Heaters Explained: Tank vs Tankless, Gas vs Electric, 6 vs 10 Gallons
How RV water heaters work: tank vs tankless, propane, electric or both, 6 vs 10 gallons, the Suburban, Atwood, Dometic and Girard lines, and replacing one.
- RV Water Pump Problems: No Pressure, Pulsing, Running Constantly, Not Turning On
Why an RV water pump will not turn on, runs constantly, pulses or gives no pressure, and the checks in order from the pump makers' manuals.
- RV Water Pumps Explained: GPM, PSI, 12 V Draw and Choosing a Replacement
How a 12 V RV water pump works, what GPM, PSI and amp draw mean, fixed vs variable speed, accumulators, and the Shurflo, Remco and Flojet lines by spec.
- Soft Starts for RV Air Conditioners: What They Change and What They Do Not
What a soft start does to an RV air conditioner's starting surge, the Micro-Air, Dometic and SoftStartRV units, fitting one, and what it does not change.
- Tankless RV Water Heaters: What the Specs Mean and What Changes in Use
How on-demand RV water heaters work, what BTU, flow and temperature rise mean, retrofitting one into a tank opening, and the trade-offs makers describe.
- The RV Propane Regulator: How It Works, Signs It Is Failing, Replacing It
What an RV propane regulator does, two-stage and auto-changeover types, the pressure it should deliver, signs it is failing, and the hoses that connect it.