Rinnai Tankless Error Code 25: What a Condensate Trap Error Means for East Cooper Homes

If your Rinnai condensing tankless stops making hot water and the display shows Code 25 in Mount Pleasant, Daniel Island, or somewhere else in East Cooper — here's the short version.

Code 25 is a condensate trap error. On Rinnai's list, that means the condensate container is full. The heater is protecting itself because condensate isn't draining the way it should. Unlike Code LC (which often keeps running while it beeps), Code 25 typically takes the unit out of service until the drain path or trap is sorted out.

I'm Christian with Avery & Sons Plumbing + Tankless. We work these units all over Charleston, and Code 25 shows up on condensing models when the condensate system — trap, drain line, or sometimes a condensate pump safety switch — isn't doing its job.

What the unit is doing

Condensing tankless heaters pull extra heat out of the exhaust. That process makes acidic condensate (water) that has to leave the unit through a trap and drain line. The trap has a level circuit. When the container is full — or the circuit sees a drain fault — Rinnai throws Code 25.

Rinnai's remedy language is blunt: condensate container is full; check the condensate drain for blockage; replace the condensate trap if needed. On installs that use a condensate pump with a safety switch wired into the trap circuit, a failed pump can also force a Code 25 shutdown so the heater doesn't keep making water with nowhere safe to send it.

If you're comparing codes: we already covered Code 10, Code 11, Code 12, Code 14, Code 16, Code 03, and Code LC for East Cooper homes. Code 25 is about condensate drainage on condensing units — not ignition, flame, overheat, scale, or Bath Fill.

Common causes we see around here

Blocked or kinked drain line. Leaves, dirt, bugs, or a crushed section of tubing can stop condensate from leaving. Around Charleston and the rest of East Cooper, outdoor runs and attic routes get abuse from heat, UV, and critters.

Poor slope or a submerged outlet. The line needs to drain downhill to an approved termination with an air gap. If the end sits in standing water — a clogged floor drain, a full bucket, a jammed laundry sink — the trap can't empty and Code 25 follows.

Failed condensate pump or safety switch. When the heater sits below the drain point, a pump moves condensate uphill. If that pump dies or its safety switch closes, Rinnai can show Code 25 and shut down on purpose.

Internal trap clogged or a bad trap/sensor. Scale, debris, or a failed level circuit inside the cabinet can trip the same code even when the external hose looks fine. Rinnai's fix path includes replacing the condensate trap when the drain check doesn't clear it.

Missing or disconnected drain after a remodel. We've seen lines pulled during laundry-room or garage work and never put back right. No path out means a full trap.

Safe checks you can do yourself

Keep it simple. If you smell gas, leave the area and call your gas utility first — don't troubleshoot.

1. Confirm the display. Write down Code 25 exactly. Note whether you have a condensing model (plastic condensate trap/drain) and whether a condensate pump is in the path.

2. Look at the drain line from outside the cabinet. Is it kinked, crushed, disconnected, or ending in a puddle? Clear what you can see without opening the heater. Restore slope if a hose got yanked sideways. Make sure the outlet has an air gap and isn't underwater.

3. If you have a condensate pump, check whether it's powered and whether the reservoir is full. A silent pump with a full tank is a common Code 25 story.

4. Do not open the cabinet, pull the trap, or bypass the safety wiring unless you're trained for it. Condensate is acidic, and the level circuit is there for a reason. Don't keep power-cycling hoping the code disappears — if the trap is still full or the drain is still blocked, it will come right back.

Gas appliances aren't where you get curious. Drain inspection from the outside is fine. Trap replacement and pump wiring are pro work.

When to call a pro

Call if Code 25 won't clear after you've confirmed the external line isn't kinked or submerged, if you don't have a condensate drain connected at all, if the pump isn't moving water, if hot water is out and you need it restored safely, or if the code returns after someone only reset power.

A proper service visit checks the drain path, trap, and (when used) pump safety circuit the way Rinnai intends, then replaces the trap if the level circuit or internal container is the problem. Around Charleston, Daniel Island, Mount Pleasant, and the rest of East Cooper, most Code 25 calls come down to a blocked line, a bad slope, or a pump that quit — not a mystery inside the burner.

Soft next step

If your Rinnai is throwing Code 25 and you'd rather not guess — Avery & Sons Plumbing + Tankless can clear the drain path, check the trap, and get the unit back online the right way. Call (843) 305-5555 or visit averysplumbing.com. We're local, we work these condensing units every week, and we'll tell you what it needs.

Don't ignore a full condensate trap — Code 25 is the unit shutting down before condensate has nowhere safe to go.