Code 29 with no hot water
The display shows code 29 and the unit will not stay lit long enough to make hot water.
Start here: Check for a blocked condensate drain or outside vent obstruction first.
Tankless water heater error code help
Rheem Tankless Water Heater Code 29
Direct answer: Rheem tankless water heater code 29 usually means the unit is detecting a venting or condensate problem. The most common homeowner fixes are clearing a blocked condensate drain, opening a sagged or kinked drain hose, or removing debris or ice at the vent termination.
Most likely: Start with the easy physical checks: look for water inside or under the unit, inspect the condensate drain path, and check the vent termination outside for blockage. If the code comes back after those checks, the problem is often inside the venting or combustion side and that is usually a service call.
When this code shows up, the heater may lock out, give only brief warm water, or stop heating altogether. Reality check: a lot of code 29 calls end up being a simple drain or vent issue. Common wrong move: resetting it over and over without checking for trapped condensate or a blocked vent cap.
Don’t start with: Do not start by buying a control board or taking apart the burner section. Code 29 is more often caused by drainage or vent restriction than by an electronic failure.
If you see water in the cabinet or dripping below the heater,check the condensate drain line and trap path before anything else.
If the code started during freezing weather or after wind-driven rain,look outside at the vent termination for ice, debris, or a shifted screen.
Last reviewed: 2026-04-17
What code 29 usually looks like in the field
Code 29 after a reset
The heater runs briefly after power cycling, then faults again once it starts heating hard.
Start here: Look for a partial drain blockage, a sagging condensate hose, or a vent issue that shows up only under load.
Code 29 with water under the unit
You find moisture in the cabinet, rust streaks, or a small puddle below the heater.
Start here: Inspect the condensate path and stop if water has reached wiring or gas components.
Code 29 in cold or stormy weather
The error started after freezing temperatures, wind, or heavy rain.
Start here: Inspect the vent termination outside for ice, leaves, nesting material, or water intrusion.
Most likely causes
1. Blocked or kinked tankless water heater condensate drain line
This is the most common homeowner-level cause. Condensate backs up, the unit senses trouble, and code 29 appears during operation.
Quick check: Look for a hose that is pinched, sagged full of water, clogged with slime, or not draining into its normal outlet.
2. Vent termination blocked by debris, ice, or insect nesting
A restricted intake or exhaust can trigger the same fault pattern, especially after weather changes or long periods without service.
Quick check: Inspect the outside vent opening for leaves, lint-like buildup, snow, ice, or a damaged screen.
3. Water intrusion or condensate collecting inside the heater cabinet
Moisture around the vent or condensate area can trip the fault and often leaves visible clues like drips, staining, or corrosion.
Quick check: With power off, remove only the access cover if it is straightforward and look for wet spots, rust trails, or pooled water.
4. Internal venting, combustion, or sensing problem
If the drain path and vent opening are clear but the code returns quickly, the issue may be deeper in the unit and not a good guess-and-buy repair.
Quick check: After the simple checks, note whether the unit tries to fire, whether you hear the fan, and whether the code returns immediately or only after a minute of running.
Step-by-step fix
Step 1: Start with the safe outside checks
Code 29 is often caused by something visible and simple before you ever touch the heater. This is the fastest way to separate a basic blockage from an internal problem.
- Turn the heater off at its power switch or unplug it if the plug is accessible.
- Go to the vent termination outside and look for leaves, plastic, lint, bird or insect nesting, snow, or ice.
- If there is a screen at the termination, make sure it is not packed over with debris.
- Clear only loose debris you can remove by hand. If there is ice, let it thaw naturally rather than prying on the vent parts.
- Look for obvious vent damage, a loose cap, or a section that has shifted out of place.
Next move: If you clear a blockage and the heater runs normally afterward, the fault was likely caused by restricted venting. If the vent opening looks clear or the code comes back, move to the condensate drain checks.
What to conclude: A clean, open vent rules out the easiest outside cause and points you toward condensate backup or an internal issue.
Stop if:
- You smell gas anywhere near the heater or vent termination.
- The vent pipe is loose, separated, badly corroded, or heat-damaged.
- You would need to disassemble sealed vent components to keep going.
Step 2: Check the condensate drain path for backup
On condensing tankless units, a blocked condensate path is one of the most common reasons for code 29. You are looking for trapped water, slime, or a hose that cannot drain downhill.
- Keep power off to the heater.
- Find the condensate drain line coming from the bottom or lower side of the unit.
- Trace the line from the heater to its drain point and look for kinks, sharp bends, sags, pinches, or a section lifted above the outlet that could trap water.
- If the line is removable without tools or force, disconnect it at an accessible point and check whether water drains freely.
- Flush the hose with warm water only if you can do it without sending water into the heater cabinet.
- Reinstall the line so it runs downhill without low spots that hold water.
Next move: If trapped water or sludge clears and the code stays gone, the condensate line was the problem. If the hose is clear but the unit still faults, inspect the cabinet for moisture and obvious drain issues at the heater connection.
What to conclude: A backed-up condensate line can make the heater think the venting side is not handling moisture correctly, even when the vent itself is open.
Step 3: Look for moisture clues inside and under the heater
Water marks tell you whether this is a simple drain routing issue or a bigger vent or internal condensate problem. You do not need deep disassembly to learn a lot here.
- With power still off, remove only the basic front cover if it comes off with ordinary screws and no sealed components are disturbed.
- Use a flashlight to look for rust trails, white mineral marks, wet insulation, drips, or pooled water near the lower cabinet and vent area.
- Check the condensate connection point for looseness, cracking, or signs that water has been backing up there.
- Look under the heater for fresh drips and confirm the water is coming from the unit, not from nearby plumbing above it.
- If you find light surface moisture, dry the area and note exactly where it returns after the next test run.
Next move: If you find a simple loose drain connection or obvious hose routing problem and correct it, the heater may return to normal. If you find repeated internal moisture with no simple hose issue, stop short of deeper teardown and plan on service.
Step 4: Reset once and watch the startup pattern
One controlled restart helps you tell the difference between a fixed blockage and a fault that is still active. The startup pattern also gives a tech useful information if you need to call one.
- Reinstall the cover if you removed it and restore power.
- Open a hot water tap and watch the display while listening to the unit.
- Note whether the fan starts, whether ignition is attempted, and whether the code appears immediately or only after the unit runs for a short time.
- If the heater runs normally for several minutes and the code does not return, keep checking for proper condensate drainage during operation.
- If the code returns, write down exactly how long it ran and whether you saw any new drips or heard any unusual surging or straining sounds.
Next move: If the unit now heats steadily and drains normally, you likely solved the blockage or routing problem. If code 29 returns on the first real call for hot water, the remaining causes are usually beyond safe DIY.
Step 5: Make the call based on what you found
At this point you should know whether you had a simple blockage or whether the heater needs service. This keeps you from buying the wrong part and still having the same code.
- If you cleared the vent opening or condensate drain and the heater now runs through several hot water calls without faulting, keep using it and monitor the drain path over the next day.
- If the code returns after the simple checks, schedule service and tell the technician whether you found a blocked vent, backed-up condensate, internal moisture, or a repeat fault with a clear drain line.
- If you found vent damage, cabinet moisture near wiring, corrosion, or any gas smell, leave the unit off until it is inspected.
- Do not buy a tankless water heater control board, fan assembly, or gas-side part based on code 29 alone.
A good result: If the heater stays clear through repeated use, your repair was likely a blockage cleanup or drain reroute.
If not: If the code keeps returning, the next step is professional diagnosis of the venting and combustion side.
What to conclude: You have either fixed the common homeowner causes or narrowed it to an internal fault without wasting money on guesswork.
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FAQ
What does code 29 mean on a Rheem tankless water heater?
In practical terms, code 29 usually points to a venting or condensate problem. The heater is seeing conditions it does not like around exhaust, intake, or moisture handling, so it locks out instead of continuing to run.
Can I keep using the heater if code 29 clears after a reset?
Not until you know why it happened. If a blocked drain or vent caused the code, it will often come right back under load. One test reset is reasonable after basic checks, but repeated resets are not a fix.
Is code 29 usually a bad control board?
No. Homeowners often jump to electronics too early. A blocked condensate line or outside vent issue is more common than a failed board for this code.
Why did code 29 start after freezing weather?
Ice at the vent termination or frozen condensate in the drain path is a common trigger. Check the outside vent first, then inspect the condensate line for trapped water or a section that cannot drain.
Should I clean the condensate line myself?
Yes, if it is easy to access and you can flush or reroute it without sending water into the heater cabinet. Stick to warm water and simple clearing. If the connection is brittle, hidden, or leaking at the unit, stop and get service.
When should I call a pro for code 29?
Call for service if the vent opening and condensate path are clear but the code returns, if you find internal moisture near wiring or gas parts, or if the venting itself looks damaged or loose.