Code appears and hot water stops
The unit tries to run, then throws code 25 and shuts down or limits operation.
Start here: Check the condensate drain line and trap for blockage or standing water first.
Tankless water heater error help
Rinnai Tankless Water Heater Code 25
Direct answer: Rinnai code 25 usually means condensate is not draining the way it should. Most of the time the fix is a blocked, kinked, sagging, or frozen condensate drain line, a clogged condensate trap or neutralizer, or a failed condensate pump if your setup uses one.
Most likely: Start with the condensate drain path. Look for standing water in the drain tubing, a full neutralizer, slime or debris in the trap, a pinched hose, or an outdoor drain line that froze shut.
This code is one of the more straightforward tankless faults once you look in the right place. Reality check: the heater may be fine and simply refusing to run because condensate has nowhere to go. Common wrong move: clearing one visible hose end and missing a clogged trap, neutralizer, or pump farther down the line.
Don’t start with: Do not start by replacing the control board or taking apart gas and combustion components. Code 25 is usually a drainage problem, not a burner problem.
If you see water backing up near the bottom of the unit,shut the unit off and clear the condensate path before trying resets.
If your drain line runs through a cold space or outdoors,check for ice before you assume a bad part.
Last reviewed: 2026-04-17
What code 25 usually looks like
Code clears, then comes back
A reset gets it going briefly, but the code returns during the next hot water call.
Start here: Look for a partial clog, a sagging hose that holds water, or a neutralizer that drains slowly.
Water near the bottom of the heater
You see dampness, drips, or a little puddling around the lower cabinet or drain tubing.
Start here: Stop using the heater and inspect the condensate outlet, trap, and any pump reservoir for backup.
Problem started during freezing weather
The code showed up after a cold snap, especially if the drain line runs outside or through an unheated area.
Start here: Check for a frozen condensate line before taking anything apart.
Most likely causes
1. Blocked or restricted condensate drain line
This is the most common reason for code 25. Algae, sludge, scale fines, or a kinked hose can slow the drain enough to trip the fault.
Quick check: Follow the small drain tubing from the heater. Look for sharp bends, low spots full of water, or debris at the outlet.
2. Clogged condensate trap or neutralizer
The trap or neutralizer can fill with residue and stop flow even when the hose itself looks open.
Quick check: If accessible, inspect for water sitting in the trap body, heavy sediment, or a neutralizer canister that feels full and drains poorly.
3. Frozen condensate line
A line routed through a cold crawlspace, garage wall, or outdoors can ice over and block drainage fast.
Quick check: Feel the exposed tubing and check the outlet point for ice or a solid plug during cold weather.
4. Failed condensate pump on pumped installations
If your heater drains into a small pump reservoir, the pump may be stuck, full of sludge, or not powering on.
Quick check: Look for a pump tank that is full of water, listen for no pump activity, or check whether the float is jammed.
Step-by-step fix
Step 1: Confirm this is a condensate drain problem, not a supply leak
People often chase the wrong water source. Code 25 points to condensate drainage, so separate that from a plumbing leak right away.
- Turn the water heater off at its power switch or unplug it if the plug is accessible.
- Look around the bottom of the unit and nearby piping with a flashlight.
- Find the small condensate drain tube. It is usually much smaller than the water lines.
- Check whether the moisture is coming from that drain path or from a domestic water connection above it.
- If you see active dripping from a water supply fitting, isolation valve, or relief-related piping, treat that as a separate leak issue.
Next move: If the moisture clearly traces to the condensate line or trap area, keep going with the drain checks below. If the water is coming from plumbing connections, the heat exchanger area, or somewhere you cannot clearly identify, stop and get the leak source confirmed before resetting the heater.
What to conclude: You want to make sure code 25 is not distracting you from a different water problem.
Stop if:
- Water is dripping onto wiring or electronic components.
- You cannot tell whether the leak is condensate or pressurized water.
- There is heavy rust staining, cabinet damage, or signs of long-term internal leaking.
Step 2: Check the full condensate hose run for kinks, sags, and blockage
A simple hose restriction is the most common fix and the least invasive place to start.
- Trace the condensate line from the heater to its drain point or pump.
- Straighten any sharp bends and support any low spots where water is pooling.
- If the line terminates at a floor drain, standpipe, or outside outlet, inspect the end for slime, debris, or ice.
- If the line is removable and you can do it without forcing brittle fittings, disconnect the accessible end and flush it with warm water into a bucket.
- Reconnect the line with a steady downhill path where possible.
Next move: If the line was blocked or pinched and now drains freely, restore power and test hot water. If the hose looks clear but the code returns, the restriction is likely in the trap, neutralizer, or pump.
What to conclude: A visible hose problem is the easy win. If the line is open, move closer to the unit's condensate handling parts.
Step 3: Inspect the condensate trap or neutralizer for slow drainage
A trap or neutralizer can clog internally while the outside hose still looks fine.
- With power still off, locate the condensate trap or neutralizer canister if your installation has one and it is homeowner-accessible.
- Look for standing water that does not drain, heavy sediment, or sludge buildup.
- If the neutralizer or trap has a serviceable section, clean it with warm water only unless the manufacturer instructions at the unit say otherwise.
- Rinse out loose debris and reassemble carefully so seals and tubing seat properly.
- Make sure the drain path leaves the trap or neutralizer without an uphill loop that can hold water.
Next move: If cleaning restores flow and the unit runs without the code returning, the clog was in the trap or neutralizer. If water still backs up or the code returns quickly, check whether the installation uses a condensate pump and whether that pump is moving water.
Step 4: If your setup uses a condensate pump, test that pump before buying anything
A full pump reservoir with no pumping action is a strong clue, but you still want to rule out a jammed float or sludge first.
- Locate the condensate pump if the drain line from the heater runs into a small plastic reservoir.
- Check the tank level. A full reservoir after heater operation usually means the pump is not moving water out.
- Make sure the pump has power if it plugs into an outlet that is easy to verify.
- Inspect the pump reservoir for sludge that could jam the float.
- If the float moves freely and the pump still does not run or hums without pumping, the pump is likely failed.
Next move: If cleaning the reservoir or freeing the float gets the pump moving again, run hot water long enough to confirm the code stays away. If the pump has power, the reservoir fills, and the pump still will not evacuate water, replacement is the likely fix.
Step 5: Restore operation and watch for a repeat fault
A clean drain path should keep the code from coming back. If it returns right away, the problem is either still restricted or no longer a simple homeowner fix.
- Reassemble any tubing or serviceable drain parts you opened.
- Restore power to the heater.
- Run a steady hot water call long enough for the unit to make condensate, not just a quick faucet burst.
- Watch the drain line, trap, neutralizer, or pump for normal movement of water and no backup.
- If code 25 returns after the hose, trap, neutralizer, and pump checks, stop DIY and schedule service for a deeper condensate sensor, internal passage, or installation issue.
A good result: If the heater runs through a normal hot water draw and the drain path stays clear, the repair is holding.
If not: If the code returns with a verified clear external drain path, the remaining issue needs brand-specific service diagnosis.
What to conclude: You have either fixed a common drainage fault or narrowed it down enough to avoid random parts swapping.
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FAQ
What does code 25 mean on a Rinnai tankless water heater?
It usually means condensate is not draining properly. The heater senses backup or poor drainage and shuts down to prevent water damage or unsafe operation.
Can I just reset the heater and keep using it?
You can try a reset after clearing an obvious blockage, but a reset alone usually does not solve code 25. If the drain path is still restricted, the code will come back.
Why would this happen more in winter?
Condensate lines that run through cold spaces or outdoors can freeze shut. That is a common reason this code shows up during a cold snap.
Is code 25 a bad control board?
Usually no. This code is much more often caused by a drain line, trap, neutralizer, or condensate pump problem than by an electronic failure.
Do all tankless water heaters with code 25 have a condensate pump?
No. Many drain by gravity. Only pumped installations have a condensate pump, so check your actual drain setup before buying anything.
When should I call a pro for code 25?
Call for service if you smell gas, see water inside the cabinet, cannot access the drain path safely, or the code returns after you have confirmed the external hose, trap, neutralizer, and pump are working.