The short answer
A Rheem tankless water heater in Northern Virginia shows a two-digit code on its remote or front panel when it stops. The ones we see most are 11 (it didn’t light), 12 (the flame went out), 1L (scale in the heat exchanger), 29 (the condensate drain on a condensing model) and 90 or 99 (a blocked vent). A newer IKONIC shows a letter and three digits instead, like A011.
Try this once
Rheem’s reset for owners:
- Turn off every hot water faucet.
- Turn the heater off at the remote and wait about five minutes.
- Turn it back on.
- If the code is still there, unplug the heater for 30 seconds and plug it back in.
If it comes back after that, call. And if the code isn’t on Rheem’s chart at all, Rheem says to call right away.
$99 Water Heater Flush
We drain and flush the tank, check the anode rod and test the relief valve, then go through the house's plumbing with photos, included. See the flush
Want your own number before anyone comes out? The water heater estimator prices your house in a few questions.
The numeric codes
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| Code | What it means | What to check |
|---|---|---|
| P1 | Not enough water flow | It needs at least 0.4 gallons a minute to fire: open the faucet more, or the inlet filter is clogged |
| 1L | Scale in the heat exchanger | It needs a descale |
| 05 / 28 | Heat exchanger running too cool | 05 is a warning, 28 if it keeps happening |
| 10 | Wrong air volume | The vent or the blower. Locks the heater out. |
| 11 | No flame after two tries | Is the gas valve to the heater fully open? |
| 12 | Flame went out three times | Gas interrupted, or a propane tank running low |
| 14 | Overheat limiter tripped | Usually the gas supply or the venting |
| 15 | Water over 207F | Call |
| 16 | Outlet temperature sensor | Call |
| 29 | Condensate not draining | Condensing models only |
| 31 to 35 | A temperature sensor | The sensor or its connection |
| 61 | Blower speed wrong | The blower motor |
| 66 | Bypass motor | The bypass valve motor |
| 70 | Control board | The board |
| 71 | Gas valve circuit | Heavy scale can cause it; a second descale may clear it |
| 88 | Maintenance reminder | Time to descale; it clears after |
| 89 | Exhaust too hot | Condensing models. Call. |
| 90 | Vent blocked before lighting | Clear the intake and exhaust outside |
| 99 | Vent blocked after shutdown | Same, and it locks the heater out |
10 and 99 lock the heater out. The remote flashes UL, and only a technician’s reset on the board clears it, after the cause is fixed.
IKONIC codes
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| Code | What it means |
|---|---|
| A011 | Didn’t light after up to 10 tries: is the gas valve open? |
| A012 | Flame lost 15 times |
| A014 | Overheat limiter |
| A018 | Scale in the heat exchanger |
| A029 | Condensate not draining |
| A090 | Vent blocked |
| T113 | Flow under 0.4 gallons a minute |
| T111 | Service reminder |
11 and 12 in winter
A tankless burns a lot of gas at once, so it’s the first thing in the house to notice a gas problem: a gas line sized for less, the furnace and the tankless firing together on a cold morning, a propane tank running low, or gas work on the street. If 11 comes back after a reset, look at the gas valve on the pipe into the heater. Our tankless problems guide covers the rest. If you smell gas, don’t flip any switches: leave the house and call your gas company or 911 from outside.
1L, 88 and scale
Northern Virginia’s hard water leaves scale in the heat exchanger, and the heater counts on it. Rheem’s fix is a descale: a small pump circulates about 2 gallons of white vinegar through the heat exchanger for 45 to 60 minutes, through the isolation valves on the pipes, then the code is cleared. Rheem says to do it regularly, and on the IKONIC, once a year. Our tankless descale is $300, regularly $350, and our tankless maintenance guide explains what’s included.
29: condensate
Condensing models make acidic water that drains out through a small line. Rheem’s checks: the protective plug on the drain fitting was removed at install, the drain line isn’t blocked or pinched, and there’s no P-trap added to the line. A frozen line in a garage or crawl space does it too.
90 and 99: the vent
Walk outside and look at the vent ends. Rheem wants 12 inches of open space at the air intake. Snow, leaves, a nest or a shrub that grew in is enough. Clear it, then reset once. 99 needs a technician’s reset even after the vent is clear.
Freeze protection
The heater’s freeze protection only works while it’s plugged in and has power, and Rheem’s warranty doesn’t cover freeze damage. In a long winter outage with a heater in a cold spot, draining it is the safe move. We can show you how.
What not to do
Don’t keep resetting a code that comes right back, don’t run the heater with a vent you know is blocked, and don’t open the cover: there’s gas and 120 volts inside. Don’t unplug it for the winter to save power, either.
What a technician does
We check the gas pressure with the heater at full fire, look at the venting end to end, clean the inlet filter, descale if it needs it, and test the part the code points at. You get the price before we fix anything. If the tankless is near the end and you’re thinking about a tank, the water heater estimator shows the installed price of a new tank, and $500 comes off it.
Related: Rinnai tankless codes, Navien codes, Rheem tank blinking light, how old is my Rheem, water heater service and our error codes guide.
Every code meaning here comes from Rheem’s own documents: tankless troubleshooting manual, IKONIC service manual, condensing tankless manual, non-condensing tankless manual and tankless install guide.
Call or book
A plumbing diagnosis visit is $49, or $250 after hours, and you get the price of the fix before we start. Call (703) 997-9757, day or night, and tell us the code. Every current deal is on our offers page. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
Questions people ask
What does error code 11 mean on a Rheem tankless water heater?
The heater tried to light twice and didn’t see a flame. Check that the gas valve to the heater is fully open, then reset once. If it comes back, the gas supply, the igniter or the flame rod needs a technician.
How do I reset a Rheem tankless water heater?
Turn off the hot faucets, turn the heater off at the remote for about five minutes and back on. If the code stays, unplug it for 30 seconds. Codes 10 and 99 need a technician’s reset.
What does 1L mean on a Rheem tankless?
Scale has built up in the heat exchanger. It needs a descale with white vinegar, then the code is cleared on the board.
What does code 29 mean on a Rheem tankless?
On a condensing model, the condensate isn’t draining. The drain line is blocked, pinched, frozen or has a P-trap it shouldn’t have.
