RV water heater won't light on propane: safe checks

Most modern RV water heaters use direct spark ignition for propane mode. When you turn the switch on, the board needs 12V power, then it opens the gas valve and sparks. If flame is not proven, the board locks out.

1. Confirm the tank is full before heating

Do not run any water heater empty. Open a hot faucet until water flows steadily with no air bursts. If the heater was winterized, confirm the bypass valves are returned to normal before attempting propane or electric heating.

2. Verify propane supply

Light a stove burner and watch for a steady blue flame, then turn it off. If the propane cylinder was recently changed, air may still be in the line. Try one normal water-heater reset after supply is confirmed. Do not keep cycling if odor develops.

3. Check 12V controls

The propane burner still depends on 12V DC for the switch, control board, gas valve and igniter. Check the RV fuse panel and measure voltage if you are comfortable with safe DC testing. A weak battery or poor ground can make the heater act like a propane problem when the real issue is control power.

4. Listen for the ignition attempt

• No click: switch, fuse, board, thermostat, limit circuit or wiring may be stopping the sequence.
• Clicking but no ignition: propane supply, burner obstruction, electrode, gas valve or gas pressure may be involved.
• Lights then shuts off: flame sensing, grounding, electrode position or unstable combustion may be the issue.

5. Inspect the exterior compartment

With the heater off and cool, open the outside access door. Look for insects, nests, loose visible wires, water intrusion or obvious soot. Do not push tools into the burner tube or gas orifice. Do not adjust air shutters unless the manual and training support it.

6. Check for lockout and reset properly

Many heaters turn on a fault light after failed ignition. Turn the water-heater switch off, wait as directed by the manual, then try one reset after basic supply checks. Repeated lockout is information. It is not an invitation to keep trying until something ignites late.

Start with the safe water-heater sequence

Confirm the tank is full and the bypass is not fooling you

Water-heater diagnosis should never begin with the burner. Open a hot faucet until water flows steadily without air. Then confirm the winterizing bypass valves are in normal position. If the tank is empty, electric elements can burn out quickly and propane operation is unsafe. If the bypass is wrong, the heater may light normally but the faucet still delivers cold or lukewarm water.

Understand the DSI fault light

A direct-spark ignition fault light means the control did not prove normal propane operation. It does not automatically name the bad part. The cause may be air in the propane line, low LP pressure, low 12V control voltage, a blocked burner tube, bad ground, electrode issue, gas valve issue or a board problem. Record what you hear: no click, clicking with no flame, flame that lights and drops out, or a delayed boom. That timing is valuable.

One reset is information; repeated resets are not a repair

After confirming propane supply and water in the tank, one normal reset after the manual-specified lockout period is reasonable. If the fault returns, stop cycling the heater. Repeated failed ignition can leave unburned gas at the burner and can create delayed ignition. Do not try to manually light a DSI water heater.

Look outside, but do not adjust gas parts blindly

With the heater off and cool, open the exterior access panel. Look for insect nests, loose visible wires, heavy soot, water intrusion, debris or a damaged electrode wire. Do not poke the gas orifice, bend the electrode by guesswork or adjust air shutters without the manual and training. Gas pressure and combustion checks require proper tools.

Related water-heater pages

• RV water heater has no hot water
• Works on propane but not electric
• RV water heater only lukewarm
• Water heater electric and propane guide
• RV propane regulator symptoms

FAQ

Why does the fault light come on?

The control did not prove normal operation, often because flame was not established or sensed. Use the manual for your exact model's fault behavior.

Can low propane pressure affect only the water heater?

Yes. Different appliances have different burner demands and ignition sensitivity. Weak pressure can show up first on one appliance.

What if the water heater works on electric?

That confirms the tank can heat water, but it does not prove the propane burner, gas valve, electrode or flame-sense circuit is working.

Brand-specific notes without guessing at parts

Suburban, Dometic and older Atwood-style water heaters may place reset buttons, boards, switches and exterior components differently. The model label is usually behind the outside access door. Use it before ordering an electrode, board, gas valve or thermostat. A correct diagnosis starts with the sequence, but a correct repair needs the exact model.

Distinguish no-ignition from no-hot-water

A water heater can fail to light and produce no hot water, but no hot water can also come from bypass valves, an outside shower cross-mixing hot and cold, a failed electric element, a tripped high-limit, or simply using the tank faster than it can recover. If the burner lights and stays lit but the faucet is cold or lukewarm, move to plumbing and mixing checks instead of ignition parts.

What to tell a technician

Report whether the heater clicks, whether the fault light appears immediately or after several tries, whether it ever lights, whether electric mode works, whether the tank is full, and whether any propane odor or soot is present. That short list can point service toward control power, ignition, flame proving, propane supply or plumbing before the access door is even opened.