Rheem Tankless Water Heater Error Codes: Full List

Quick Answer

Rheem tankless water heater error codes: P1 = low gas pressure, P2 = ignition failure, E5 = overheating, C7 = flame sensor fault. Find your code in the list below. Most Rheem codes require checking gas supply, venting, or the heat exchanger for scale. Annual descaling extends unit life significantly.

Rheem tankless units are seriously sensitive to gas pressure and intake air quality. When one throws a code, it's almost always a safety lockout to prevent a dry fire or carbon monoxide buildup. Honestly, most of the service calls I run for these codes trace back to skipped annual maintenance, not a dead component. Descaling and cleaning the flame rod fixes probably 60% of what I see.

RheemWaterheater

About These Rheem Waterheater Error Codes

These error codes are your water heater protecting itself from expensive damage. A flashing code usually points to one specific sensor that's out of spec. Before you buy any parts, check the gas shut-off valves and look inside your intake PVC pipes for spider webs or debris. I've found wasp nests in there twice this summer alone.

Most Common Error Codes

Ignition lockout from failed or dirty ignitor40%

Flame sensor not detecting pilot or burner flame24%

Air/exhaust venting blockage triggering safety shutdown14%

Gas pressure below minimum spec (3.5 inches w.c.)12%

Scale buildup in heat exchanger restricting flow10%

Symptoms You May Notice

No hot water output
Error code displayed on LCD panel
Unit attempts to fire then shuts off
Hot water is cold or lukewarm only
Unit clicks multiple times then displays a code

Tools Required for Diagnosis

Phillips #2 screwdriverFlathead screwdriverAdjustable wrenchDigital multimeterNeedle-nose pliersDescaling pump kit5-gallon bucketWhite vinegar or commercial descaler solutionManometer or gas pressure gaugePipe thread tape (Teflon)

How to Identify Your Error Code

Frequently Asked Questions

How do I read error codes on a Rheem tankless water heater?

The LCD on the front panel is your starting point. If it's blank, check that the unit's got power first. To pull up the error history, press and hold the up and down arrow buttons together for about three seconds. The display cycles through the last several faults the unit logged. That's really useful for catching intermittent stuff that disappears when you reset the power. I've had calls where the homeowner said 'it's fine now' but the history showed Code 11 six times in the past week. Don't ignore what that history mode is telling you.

What is the most common error code on a Rheem tankless water heater?

Code 11 is hands down the most common call I get on these units. It means the unit tried to ignite but couldn't confirm a flame. Usually I find a thin white oxidation layer on the flame rod, or there's a tiny spider web in the burner orifice. A quick cleaning usually does it. But you should also verify your gas meter can deliver enough flow for the unit's BTU demand, especially if you added this heater to an existing gas line that's already loaded up with other appliances.

Can I reset a Rheem tankless water heater error code myself?

Yeah, you can try. Unplug it for a full 60 seconds so the capacitors drain completely, then plug it back in. If the code comes right back, the unit's telling you a safety sensor is still detecting a problem. Don't just keep resetting it and hoping something changes. I've seen people burn out igniters doing that. Figure out what the specific code means, fix the root cause, then reset. Resetting without fixing is just delaying the same problem.

Are Rheem error codes the same as Rinnai or Noritz codes?

Don't assume they are. Code 11 is pretty much universal for ignition failure across brands, but after that it gets brand-specific fast. A Rheem E5 is an overheat fault. That same number on another brand might mean something completely different. Stick to the Rheem service manual for your specific model. I've seen people replace the wrong part entirely because they looked up a code from the wrong brand's documentation online.

Does Rheem offer a warranty on tankless water heater repairs?

Rheem's warranty is actually pretty solid. Heat exchanger is usually covered 12 years, parts for 5 years. But here's the catch: they want proof of professional installation and annual maintenance records. If you DIY'd the install or haven't descaled in three years, they might push back on a warranty claim. Keep your receipts and service records somewhere you can find them. It's way easier to win that argument when you've got documentation backing you up.

How often should I descale my Rheem tankless water heater?

Every year if you're in a hard water area, every two years if your water's reasonably soft. Honestly most homeowners don't do it often enough, and that's why I see so many units throwing overheat codes at 4 or 5 years old when they should have 15 years left in them. Scale is basically insulation inside your heat exchanger, and once it gets thick enough the unit can't transfer heat efficiently. A $30 bottle of descaler and an afternoon every couple of years adds real years to the unit's life.

What should I do if my Rheem tankless keeps showing the same error code after resetting?

Stop resetting it. Repeatedly resetting a unit with an active fault can damage the igniter or stress other components over time. Look up what that specific code means, then start with the cheapest and easiest checks first: gas valves, inlet filter, venting. If you've worked through all that and it's still throwing the same code, it's probably time to call a tech. At that point you're likely looking at a failed sensor or a control board issue, and those need a multimeter and some experience to diagnose properly.

Related Rheem Waterheater Error Codes

Code: 11Rheem Tankless Water Heater Code 11: Ignition Failure Fix

Same Fix on Other Brands

Rinnai waterheater11: Rinnai Code 11: No Ignition Noritz waterheater11: Noritz Code 11: No Ignition

Models Known to Experience HUB Errors

This repair applies to most Rheem waterheaters with this error code. Common model numbers include:

RTGH-95DVLN, RTGH-84DVLN, RTG-95XLN, RTG-84XLN, RTGH-95DVLP, RTGH-84DVLP, RTG-70DVLN, RTGH-RH10DVLN

Written by

Raj Patel

HVAC & Water Systems Specialist · 15 years experience

Last verified for technical accuracy on March 14, 2026