Rheem Tankless Water Heater Error Codes: 11, 12, 29, 90

By Ray Bennett · Updated 2 October 2026 · 6 min read · Checked against the maker’s manual

Rheem Tankless Water Heater Error Codes: 11, 12, 29, 90

Short answer

Rheem tankless heaters show a two digit code, and condensing models show the same fault with A0 in front, so 11 and A011 are one fault. 11 means the gas shut-off valve is not fully open, 12 that the gas has been interrupted or the propane is low, 29 a blocked condensate line, and 90 or 99 a blocked air intake or vent.

A Rheem tankless water heater shows an error code on its display or remote when its diagnostic system finds a problem. Four of the codes have a fix you can do yourself, and Rheem’s own chart says the rest need a dealer or a qualified technician.

Everything on this page comes from Rheem’s use and care manuals: AP22745 for its condensing tankless heaters and AP22009 for its non-condensing tankless heaters, indoor and outdoor. The non-condensing manual covers Rheem, Ruud and Richmond models, so the same codes apply to those names.

Before you start

What to carry: a torch and a pen, and a soft brush for the water filter. Ten minutes to read the code, half an hour for the filter.

Gas or electric? These charts are for Rheem’s gas tankless heaters, natural gas or propane.

Two ways of writing one code. Non-condensing models show two digits, such as 11. Condensing models show the same fault as A011, with A0 in front.

Turn off the hot taps first. Rheem’s steps for clearing a code start with every hot water faucet off.

What Rheem says not to touch. Power off before the cover comes off. Rheem says to make certain the power to the heater is off before removing the protective cover for any reason, because of the shock hazard.

Leave the gas and the controls to a technician. Rheem says not to attempt repair of electrical wiring, gas piping, the heater control, burners, vent connectors or other safety devices. If the code on your display is not in the chart, Rheem says to turn the heater off at once and call for service.

How Rheem writes its codes

A condensing Rheem adds A0 in front of the same two digits, so 11 and A011 are the same fault.

Check 1Free, two minutes

Read the code and try clearing it

Read it. The code shows on the heater’s display or on the remote control.

Clear it on a condensing model. Rheem’s steps: turn off all hot water faucets, press SERVICE, then ENTER, use the arrows to reach “Clear Alarms?”, press ENTER, choose “Yes” and press ENTER again. Press BACK to return to the main screen.

If it comes straight back. Rheem says to turn off the hot water faucet, turn off the heater, note the code and call for service.

If there is no code at all. Rheem’s no hot water list starts with simpler things: the heater switched off, a water shut-off valve not fully open, frozen pipes or a clogged water filter: what goes wrong with tankless water heaters.

Every code in Rheem’s chart

Non-condensing	Condensing	What Rheem says it means	Rheem’s answer
1L	A01L	Lime deposits building up	Dealer or technician
11	A011	Gas shut-off valve not fully open	Open it completely
12	A012	Gas service interrupted, or propane running low	Gas utility, or refill the tank
14	A014	Water heater overheating	Dealer or technician
None	A029	Blocked condensate line	Dealer or technician
31	A031	Faulty inlet water thermistor	Dealer or technician
None	A032	Faulty heat exchanger thermistor	Dealer or technician
33	A033	Faulty outlet water thermistor	Dealer or technician
None	A035	Improper thermistor connection	Dealer or technician
None	A036	Faulty exhaust thermistor	Dealer or technician
None	A055	Faulty gas valve	Dealer or technician
61	A061	Faulty blower motor	Dealer or technician
None	A063	Built-in recirculation pump, SR models only	Dealer or technician
None	A065	Faulty water flow solenoid	Dealer or technician
66	A066	Faulty bypass motor or solenoid	Dealer or technician
None	A070	Faulty control board	Dealer or technician
None	A071	Faulty gas solenoid valve	Dealer or technician
None	A072	Flame detected before ignition	Dealer or technician
None	A082	Software error	Dealer or technician
90 or 99	A090	Air intake or vent blocked, or vent pipes not connected properly	Clear any blockage
P1	T113	Not enough water flow to run	Open the tap further
88	T111	Reminder to flush the heat exchanger or change the water treatment filter	Dealer or technician

The four codes you can fix

These four are the only codes where Rheem's chart gives the owner a fix. Everything else goes to a dealer or technician.

Check 2Free, ten minutes

Work Rheem's owner fixes

11: the gas valve. Rheem says the gas shut-off valve is not fully open. Check the manual valve on the gas line to the heater and open it completely.

12: the gas supply. Rheem says gas service has been interrupted, so contact your gas utility. On propane, Rheem says the tank may be running low: refill or replace it.

90 or 99: the air. Rheem says the air intake or vent exhaust opening may be blocked. Remove the blockage, and keep 12 inches of clear space around the air intake. If the vent pipes may not be connected properly, Rheem says to call a technician.

P1 or T113: the flow. Rheem says there is not enough water flow to run the heater. Open the hot tap further, because a tankless heater will not fire on a trickle.

The monthly filter clean

Check 3Free, thirty minutes

Clean the water filter the way Rheem says

How often. Rheem’s preventive maintenance list says to check and clean the water filter monthly. A clogged filter is on its list of causes of no hot water.

Shut it down. Turn off the heater and disconnect its power, turn off the water supply to it, then drain it as its manual describes.

Take the filter out. Rheem says to unscrew it from the base of the cold water inlet line and slide it out carefully. Do not tap or force it, because that can deform it.

Clean it. Rinse it under running water, with a soft brush for heavy sediment.

Put it back. Screw it back in until snug, not tight, because Rheem warns overtightening can damage it. Turn the water on, restore power and turn the heater on.

When it needs a technician

Check 4

Know when to stop

1L, 88 and T111. Lime building up in the heat exchanger, and the reminder to flush it. Rheem sends both to a dealer or technician: why scale slowly starves a tankless heater.

14 and A014. The heater is overheating. Rheem sends this to a dealer or technician.

A029. A blocked condensate line on a condensing heater. Rheem sends it to a dealer or technician to clear.

The thermistor, gas valve, blower and board codes. 31, 33, 61, 66 and the A03 to A08 codes are parts inside the heater. That is technician work.

A072, flame before ignition. Rheem’s chart lists flame detected before the heater tried to light. Turn the heater off and call for service.

Questions people ask

What does code 11 mean on a Rheem tankless?

Rheem’s chart says the gas shut-off valve is not fully open. Open the valve on the gas line to the heater completely. On condensing models the same code shows as A011.

What does code 12 mean?

Gas service has been interrupted, so Rheem says to contact your gas utility. On a propane heater, the tank may be running low and needs refilling.

What does 29 mean on a Rheem tankless?

On condensing models, A029 is a blocked condensate line. Rheem’s chart sends it to a dealer or qualified technician.

What do 90 and 99 mean?

Rheem says the air intake or vent exhaust opening may be blocked. Remove the blockage and keep 12 inches clear around the intake. If the vent pipes may be loose, call a technician.

How do I clear a code on a Rheem tankless?

On condensing models, turn off the hot taps, press SERVICE then ENTER, go to “Clear Alarms?”, and choose “Yes”. If the code is still shown, turn the heater off and call for service.

What does 88 mean?

A maintenance reminder. Rheem says it is time to flush the heat exchanger or replace the water treatment filter, and to contact a dealer or technician.

Sources: Rheem use and care manuals AP22745 (condensing tankless) and AP22009 (non-condensing Eagle tankless, indoor and outdoor)