Before you start: Propane safety: if you smell gas, see soot, hear a boom at ignition, or find burned wiring, turn the water heater and propane supply off and get qualified RV propane service.

Dometic has sold several RV water-heater families over the years, including direct-spark ignition units that owners often call “DSI water heaters.” The exact service manual for the installed model always wins, but the basic sequence is the same: the tank must be full, the control board needs 12V power, the gas valve opens, the igniter sparks, and the board must prove flame.

Start with the two things that get missed

First, make sure the water-heater tank is full. Open a hot faucet until water flows steadily with no air. Second, confirm the winterizing bypass valves are not still in bypass. A heater can act “dead” or produce only lukewarm water when the plumbing is still set for storage.

Read the DSI fault like a clue

If the DSI or fault light comes on, the heater tried and did not prove normal propane operation. That can be empty LP lines, low 12V power, a weak ground, blocked burner, poor electrode gap, failed gas valve, dirty flame-sense path, or a control-board problem. Reset once after checking supply. Do not keep cycling a propane appliance that is failing to light.

Listen outside during one ignition attempt

  • No click: look at switch power, fuse, thermostat/high-limit circuit, board power and ground.
  • Clicking but no flame: check LP supply, air in the line, burner obstruction and gas-valve operation.
  • Lights then goes out: suspect flame sensing, ground path, electrode position or unstable flame.

Check the burner area without adjusting gas parts

With the heater off and cool, open the exterior access door. Look for mud daubers, spider webs, loose visible wires, water intrusion, heavy soot or a damaged electrode lead. Cleaning obvious debris around the compartment is owner-level work. Gas pressure, orifice cleaning, valve testing and board output checks belong to a technician.

Common false trails

A stove burner lighting does not prove the water heater has correct gas pressure under all conditions. A good spark sound does not prove the gas valve opened. A new control board will not fix a weak ground or blocked burner tube. Work the sequence instead of guessing.

Tools, difficulty and likely cost

  • Difficulty: Beginner for observation, cleaning and reset checks; professional for live 120V, propane pressure, sealed refrigeration or internal control testing.
  • Useful tools: Flashlight, Water-heater model number, Owner manual, Basic DC voltmeter if trained.
  • Likely cost: Free for bypass, reset and supply checks; service calls commonly depend on burner cleaning, electrode work, gas valve testing or board diagnosis.

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FAQ

Why does my Dometic water heater click but not light?

The control is trying to ignite, but propane flow, burner condition, electrode position, gas pressure, ground path or flame sensing may be failing.

Can I manually light a Dometic DSI water heater?

No. Direct-spark ignition water heaters are designed to light electronically. Do not bypass the ignition system.

Why does it work on electric but not propane?

That usually means the tank and plumbing can heat water, but the propane burner side still has an ignition, gas supply, flame-sense or control problem.

Still narrowing it down?

The guided troubleshooter walks through the symptom in a safe order and points you toward the right system.

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