Rinnai Code 25: Bath Fill Error (ThermaCirc Models)
Quick Answer
Rinnai Code 25 is exclusive to models with a built-in bath fill or recirculation feature. The unit was commanded to fill a bathtub or run a recirculation cycle but did not detect that the operation completed within the set time window.
Code 25 is rarely a part failure. It usually pops up because someone installed a massive soaking tub or the flow rate slowed down over time from scale buildup. It's a timer issue, not a broken heater. You'll still have hot water for your shower, but the smart fill feature just timed out before the tub hit the sensor. Ignore it and the auto-fill just won't work anymore.
Think of this as a safety timeout. The Rinnai controller has a stopwatch running while it fills your tub. If that stopwatch hits the limit before the water reaches the target, it shuts down to prevent an overflow. I usually see this after a bathroom remodel where the new faucet has a lower flow rate than the old one.
Most Likely Causes
Based on aggregated repair data, here is the probability breakdown for this error code:
Bath fill time limit set too short for the volume of the bathtub40%
Low water flow rate through the bath fill hot water line24%
Recirculation pump not operating or operating at reduced capacity14%
Scale buildup reducing flow through the supply piping to the tub12%
Bath fill valve or mixing valve not opening fully10%
Symptoms You May Notice
Code 25 flashes on the controller display right after you kick off a bath fill cycle
Tub is only half or three-quarters full when the error appears and the water cuts off
Bath fill worked fine for years, then suddenly started cutting off early after plumbing work or a new tub install
All your other hot water is totally normal, showers and sinks work perfectly fine
You can hear the fill valve motor running but the tub never finishes filling before the code shows up
Can you reset a Rinnai waterheater to clear the 25 code?
To clear the code, just cycle the power button on your digital controller. Since this is a functional timeout rather than a hard lockout, the heater is ready to go immediately. I recommend bumping up your bath fill time limit by five minutes before you try running the water again to ensure the timer does not trip a second time.
Tools Required for Diagnosis
5-gallon bucket (for flow rate testing)Smartphone or stopwatch (for timing flow rate)Phillips #2 screwdriverFlathead screwdriverMultimeter (for testing pump motor continuity and valve actuator coil)Water pressure gauge (to check incoming supply pressure at hose bib)Flashlight
Diagnostic Checklist
Follow these steps in order. We start with the easiest external fixes before opening up the machine.
Replacement Parts
If your diagnostic testing proves the component has failed, you will need a replacement. We recommend OEM parts over aftermarket for water-handling components.
Part Name
OEM Number
Estimated Price
ThermaCirc Recirculation PumpContact Rinnai with model number · $80–$150
Contact Rinnai with model number
$80 – $150
Frequently Asked Questions
Code 25 appeared but my bathtub is actually full. What's going on?
Classic ghost error. What happens is the water hits the sensor right as the timer expires, so the controller gets two conflicting signals at basically the same moment. It sees 'tub full' and 'timer expired' simultaneously and throws the code anyway. I usually fix this by adding a three to five minute buffer to the fill timer. That gives the sensor enough time to tell the computer the tub is full before the safety clock runs out and trips the lockout. Bump the timer up a little and you probably won't see it again.
Can I disable the bath fill feature entirely to stop Code 25?
Absolutely, and honestly a lot of homeowners do this because they never use the auto-fill anyway. Get into the installer settings menu on the controller and toggle the bath fill function to OFF. Once it's disabled, the unit just ignores the timer and flow sensor for that feature completely. Code 25 won't come back. Your normal hot water for showers, sinks, dishwasher, all of that still works perfectly fine. Only the automated tub-filling feature gets turned off.
What should I actually set the bath fill timer to for my tub?
Depends on your tub volume and flow rate, but here's a quick way to figure it out. Do a manual fill and time it with your phone. Add 10 minutes to that number and use it as your timer setting. A standard 60-gallon tub at 4 GPM takes about 15 minutes to fill. But most modern soaking tubs hold 80-100 gallons, and if your flow's slow, you might need 35-40 minutes. I usually crank it to 99 minutes during testing, confirm the fill completes, then back it down to the actual fill time plus that 10-minute buffer. Simple.
My Rinnai is brand new and already throwing Code 25. Did the installer set it up wrong?
Probably a setup issue, not a defective unit. Installers sometimes skip adjusting the bath fill timer during commissioning, and the factory default doesn't match every tub size. I've seen brand new units throw Code 25 on the very first fill because the default timer was set to 20 minutes and the tub held 90 gallons. Get into the installer menu and bump that timer up. If you don't have the installer code, call Rinnai support and they can walk you through it. This is almost always just a settings adjustment, not a hardware problem.
Could low water pressure from the street cause this error?
Yeah, it can. If your incoming water pressure drops below about 30 PSI, flow rates suffer across the whole house and your tub fills noticeably slower. Timer runs out before the tub fills, Code 25. Grab a pressure gauge and check at an outdoor hose bib. Normal residential pressure runs 40-80 PSI. If you're way below that, check whether your main shutoff valve is fully open first. Could also be a failing pressure regulator valve, which is pretty common in older homes. A plumber can swap that out in an hour or two and it makes a huge difference.