Excel Tankless Water Heater Troubleshooting

The Short Answer: Excel is a compact gas tankless, not a Rinnai and not a 40-gallon. The common box is a vent-free ~38,000 BTU LP unit (JSD-10D / EX93FR class, D-cell ignition, ODS). Excel Pro is a larger vented NG/LP whole-house cousin. Cold water is empty bottles, dead batteries, no flow, a tripped ODS, a packed inlet, or a flue that will not prove. Do not crack flares. If you smell propane or see a yellow lazy flame, shut it down.

Search Intent & The Real Problem

The small white box is passing cold water, clicking, or the display is dark. Marketing said “vent-free, 2 psi startup, endless hot water.” Physics said 38,000 BTU is a one-fixture heater. People paste Rinnai 11/12 codes onto a battery igniter and a Chinese JSD board. Name the platform first. RV cousins with a real Suburban or Girard badge are not Excel — Girard, Suburban gas. Whole-house electric tankless is Powerstar, not this badge.

What other guides get wrong

They treat Excel like a condensing Rinnai: 3” PVC, code 11, a 199,000 BTU manifold. A JSD-10D class unit is ~1.6 GPM and ~38,000 BTU. They tell you to run vent-free in a sealed bedroom. They skip the D-cells, so you buy a gas valve for $3 of batteries. They paste generic E01–E05 charts that do not match your sticker. And they tell you to soap-test a smelling RV bay with the igniter still sparking.

Step-by-Step Troubleshooting

Step 1: Read the plate — vent-free JSD vs Excel Pro

• What to look for: Model (JSD-10D, EX93FR, Excel Pro, and cousins). Fuel: LP vs NG. Vent-free vs a CAT III / stainless flue. Water connections 1/2” NPT. Photo of any error digits and the sticker that defines them.
• Required tools: Flashlight, phone camera.

A vent-free Excel in a tight coach without a working ODS is a CO appliance, not a “no flue needed” feature.

Step 2: Fuel, batteries, and a real call for heat

• What to look for: LP bottles open, not empty, changeover not stuck on reserve. NG cock parallel to the pipe. Two D-cells fresh and in the correct orientation on battery-ignition models. Hydro-gen models need enough flow to spin the generator — a trickle will not spark. Powered Excel Pro: 120 V present, display alive. Manifold: LP typically ~10–11 in. w.c., NG ~3.5–7 in. w.c. vs that plate. A manometer is licensed. Do not crack a flare to “see if you have gas.”
• Required tools: LP gauge, fresh D-cells, eyes on the cock.

Other LP appliances dead in the same hour is the tank or regulator, not the Excel.

Step 3: Water flow, inlet screen, and the 1.6 GPM ceiling

• What to look for: Isolation valves open. Inlet screen packed with well sand or campground grit. Excel’s marketing is low-pressure startup (they claim a couple of psi). That is not a magic 4 GPM heater. A 2.5 GPM shower on a 38,000 BTU box in 50 °F inlet water is lukewarm with a healthy burner. That is math, not a failed exchanger. Activation is still real: no flow, no fire. House or city static over ~80 psi belongs on a regulator, not on the Excel “boost.”
• Required tools: Faucet, a jug and a watch if you need GPM. Screen cleaning with water off.

Crossover test: close cold to the heater, open a hot faucet. Pressurized flow means a mixing cartridge is dumping cold into hot.

Step 4: Ignition, ODS, and flame that will not stay

• What to look for: Spark at the burner with gas off (one look, then bottles closed if you smell it). Spark, no flame: fuel. Flame, then ODS drop: starved oxygen, blocked grille, or a bad ODS — do not bypass. Vented Excel Pro that lights then dies is flame rod, flue, or gas pressure — same family as Rinnai no hot water but not the same codes. Error digits: use the sticker in that cabinet. Do not invent 11/12.
• Required tools: View of the burner with fuel off. The sticker.

Yellow tips, soot, or a headache: shut it down. Vent-free is not a license to run a dirty burner in a camper.

Step 5: Flue (Pro), leaks, and replace vs service

• What to look for: Excel Pro: flue disconnected, bird nest, condensate in a horizontal run, or a wall termination blocked. T&P on a vented unit that dribbles: expansion or >80 psi; never cap; typical 150 psi / 210 °F. Wet cabinet, green on the copper exchanger, or a drip at a water union: isolate water, leave gas off. Parts and factory support are thin. A $200 vent-free box with a cracked exchanger is replacement, not a rebuild.
• Required tools: Eyes on the flue and the cabinet floor. Water off before any panel on a leaker.

Do not convert LP to NG as a “fix.” That is a licensed orifice/valve job or a different unit.

When DIY Ends: Calling a Licensed Pro

You may confirm bottles, swap D-cells, clean an inlet screen with the water off, and photograph a code. Stop at gas fittings, ODS bypass, flue work, combustion, and any leak into the cabinet. Vent-free Excel in a dwelling or an RV is a CO conversation with a licensed tech, not a weekend “tune.” A licensed plumber or RV tech with a manometer and a combustion sense beats another Amazon board.

Frequently Asked Questions

Q: Why is my Excel tankless water heater not getting hot? A: Empty LP, dead D-cells, packed inlet screen, no flow, a tripped ODS, or a 38,000 BTU unit asked to run a house. Check fuel and batteries, then hire a licensed tech if it still passes cold water.

Q: Does an Excel vent-free tankless need a flue? A: The small ODS units are sold vent-free. They still need combustion air, a working ODS, and a shutdown if the flame is yellow or anyone is dizzy. Excel Pro does need a flue. Do not run either with a gas smell.

Q: Can I fix an Excel tankless gas valve myself? A: No. Do not loosen gas fittings. Fuel, batteries, and the inlet screen are the homeowner list. Valves, ODS, and flues are licensed.