Rheem tankless repair: common problems and who fixes them

Safety first

If you smell gas, do not reset anything. Leave on foot, avoid anything that can spark, and call the gas utility and 911 from a safe place^[3].

Rheem's own service manual warns that diagnosis can expose a technician to live AC and DC voltage, and that the ignition cable carries more than 10,000 volts^[1]. The checks on this page stay outside the cover. Gas, venting, electrical and internal repairs belong to a licensed plumber or a technician trained on Rheem tankless units.

This page covers Rheem and Ruud gas tankless units served by Rheem's SVC820 manual, both non-condensing and condensing^[1]. Newer platforms with their own manuals may use different codes. See the full list at Rheem tankless error codes.

Common problems by symptom

Symptom	Code	Common causes	Safe owner check	Pro work
Setpoint shows, but no hot water	None or P1	Unit needs a reset, dirty inlet filter, hot and cold lines crossed, plumbing cross-over, flow too low	Reset once; clean the inlet filter; clean faucet aerators	Crossed lines, cross-over hunt
Burner will not light	11	Gas off, empty propane tank, low gas pressure	Gas valve open; other gas appliances work	Gas pressure test, igniter, flame rod
Lights, then goes out	12	Gas supply or venting problem	Note if it happens when other gas appliances run	Gas and vent diagnosis
Shuts down, venting code	10, 90, 99	Blocked vent terminal, blower not moving enough air	Clear the outside terminals	Vent and blower repair; hard lockout reset
Overheat shutdown	14, 15	Scale, restricted flow, overheat limiter	Do not keep resetting	Root-cause diagnosis
Scale warning	1L	Lime in the heat exchanger	Book a flush	Flush and descale
Condensing unit stops	29	Condensate not draining	Check the condensate line for kinks, clogs or ice	Condensate repair
Condensing unit warns or stops	92, 93	Condensate neutralizer used up	Book service	Neutralizer replacement and reset

Code meanings are our paraphrase of Rheem's SVC820 manual, not Rheem's text^[1]. Codes 10, 13 and 99 are hard lockouts that need a reset procedure after the cause is fixed^[1].

The no-code, no-hot-water checklist

Rheem's manual lists these causes when no hot water arrives^[1]:

1. The unit needs a reset. Turn the water supply off, turn the remote off, wait 10 seconds, turn it back on, then restore water.
2. Not enough flow. Open several hot taps at once. If the unit fires, one fixture alone does not draw enough flow. Rheem points to clogged faucet aerator screens as a common culprit.
3. A dirty in-line water filter. Clean it following the Use and Care manual.
4. Crossed water lines. Hot and cold connected to the wrong ports at the unit, often on a new install. A plumber fixes this.
5. A plumbing cross-over. A failed single-handle faucet or mixing valve lets cold water into the hot line. Rheem describes a fixture-by-fixture test, which a plumber can run.

What a homeowner can safely check

• Gas, water and power. Valves open, gas service on, the unit powered.
• The inlet water filter. Covered in the Use and Care manual that ships with the unit^[1].
• Vent terminals. Clear snow, leaves or nests you can reach from the ground.
• The condensate line on condensing models. Look for kinks, clogs or ice.
• One reset. If the code returns, stop and call.

Scale and the 1L code

Code 1L means the control board has detected lime build-up in the heat exchanger, and Rheem says the unit must be drained and flushed to prevent permanent damage^[1]. Rheem's procedure uses its tankless flush kit (RTG20124) with a submersible utility pump, 2 gallons of food grade white vinegar, and 45 to 60 minutes of circulation, with gas and water off throughout^[1]. Heavy scale may need more than one flush^[1]. Rheem's warranty excludes failures caused by lime, mineral build-up or scale^[2]. See how to descale a tankless water heater.

Condensing units: the neutralizer

Condensing Rheem tankless units make acidic condensate that passes through a neutralizer filled with calcium carbonate media. Code 92 is a warning that the neutralizer needs replacing; the unit keeps running for now but will eventually shut down. Code 93 means the unit will not run until the neutralizer is replaced and the unit is reset^[1]. Replacement kits come through Rheem and Ruud suppliers^[1].

What needs a licensed plumber or Rheem-trained technician

• Gas pressure, gas valve, igniter, flame rod and anything in the gas train.
• Vent repairs and hard lockout resets after a venting or combustion fault.
• Sensors, blower, water valves and the control board.
• Neutralizer replacement, if you are not comfortable with it.
• Crossed water lines or cross-over diagnosis.

Warranty basics

Rheem's residential tankless gas warranty certificate (AP21265 Rev 03) lists these periods^[2]:

Installation	Heat exchanger	Parts	Labor
Single-family home	15 years	5 years	1 year
Single-family home with controlled recirculation (on-demand, or aquastat and timer)	15 years	5 years	1 year
Single-family home with uncontrolled, continuous recirculation	3 years	3 years	1 year
Single-family home used with hydronic forced-air heating	10 years	5 years	1 year

All coverage ends after 12,000 hours of operation^[2]. Other terms in the same document^[2]:

• Start date. Coverage runs from the documented installation date. Without proof, it runs from the date of manufacture plus 90 days.
• Original owner only. The warranty is not transferable and covers the unit only at its original location.
• Installer. Rheem says the unit is intended to be installed by a contractor that is licensed, state qualified and trained on Rheem tankless products, and warranty labor must be done by such a contractor.
• Exclusions include scale, water quality outside Rheem's listed limits, improper sizing of the gas line or venting, and improper gas conversion.
• Claims need documented proof of failure by a licensed plumber, mechanical contractor or Rheem technical service. Rheem customer service is listed at (800) 621-5622.

Use our Rheem age decoder to read the manufacture date.

Repair or replace?

HomeGuide's national figures (August 2025): tankless repairs $300 to $1,300, a heat exchanger replacement $600 to $1,300, and a flush and descale $75 to $300^[4]. Rheem's own guidance: tankless units can last 15 to 20+ years with care, and when a repair costs more than 50% of a new unit, replacement is almost always the better investment^[5]. See repair or replace.

When to call a pro

• Any ignition, flame or overheat code that returns after one reset with gas confirmed on.
• Hard lockouts (10, 13, 99) and any venting code that returns after the terminals are clear.
• Sensor, blower, valve or board codes, and 93 if you are not comfortable replacing the neutralizer.
• Hot and cold lines that may be crossed, or a suspected plumbing cross-over.