Tankless water heaters

A tankless only fires when it sees enough water flow. Low flow and air in the lines cause most complaints.

The short version

• Clean the inlet screen first. It plugs up and kills the flow.
• Needs a minimum flow to fire. A low-flow showerhead or a half-open tap may not trigger it.
• Read the code on the display and look it up for that model.
• Hot then cold then hot: often a mixing or low flow problem, not the heater.

On the job

1. Open a hot tap fully into a bucket. A gallon in 30 seconds or less is enough flow to fire most units.
2. Listen: fan, then spark, then burner within about 5 seconds. Fan only = no gas or no spark. Nothing = no power or no flow sensed.
3. Read the code. Girard: E1/E2 ignition, E5/E8 air, E6 over 140°F. Furrion: E1 flame, E5 air, E6 surge. Truma: E1 no flame, W27 no water.
4. Clean the inlet filter screen (Furrion: behind the baffle). Check 11 in WC under load. Clear the exhaust of nests.
5. Reset: power off five seconds, back on. Three tries after a cylinder change is normal.

Numbers

• Minimum flow: about 0.3 to 0.5 gpm (Furrion 0.32)
• Max water pressure (Furrion): 65 psi
• Default set point: 115°F

Shop tip

If it works at the kitchen sink but not the shower, the heater's probably fine.

Try it on a service call

Put the lesson to work on a hands-on troubleshooting case.

• Water heater lights, then goes out

Keep going on water heaters

Learn it

• Tank water heaters
• Water heater gas side

Prove it

• No hot water on electric
• Water heater lights, then goes out
• Water heater lights then faults

See it in 3D

• Water heater 3D wiring model

Codes and specs

• Tank water heater: suburban + atwood dsi
• Tankless: start first
• Truma aquago
• Girard gswh-2
• Furrion fwh09

On the job

• Water heater