Rinnai Error Code 681: DHW supply temperature abnormality (Combi Boiler)
Rinnai error code 681 on a combi boiler means: DHW supply temperature abnormality. It is also called Rinnai diagnostic code 681.
Homeowner? What Rinnai code 681 means for you
Check, then call Your combi boiler is reporting: DHW supply temperature abnormality. This is often caused by something simple. Try the safe checks below; if the code returns, book a service call before it turns into a no-heat or no-hot-water emergency.
Safe things you can check yourself
- Check the thermostat: right mode (Heat or Cool), set a few degrees past room temperature, and fresh batteries if it uses them.
- Make sure the unit has power: its on/off switch (often looks like a light switch near the unit) is ON and the breaker in the electrical panel is not tripped.
- Look at the pressure gauge on the boiler. If it reads much lower than usual or near zero, or water is leaking, call a technician.
- Outside, make sure the intake and exhaust pipes or vent cap are not blocked by snow, ice, leaves or a nest.
- Check that the boiler gas valve is open (handle in line with the pipe).
- Try one reset: turn the power off for 30 seconds, then back on. If the code comes back, stop resetting and call a technician.
- If only hot water is missing, check that the hot water tap is open far enough to start the heater.
Call (647) 657-2977Book a service call
Licensed technicians serving Vaughan, Toronto and the GTA.
What does Rinnai error code 681 mean?
The measured bypass ratio, calculated from the inlet, heat exchanger and outlet thermistors, doesn't match the expected ratio — often from a misaligned bypass valve or a bad temperature reading.
Applies to: I-Series Plus Combi boilers — 150K BTU and smaller and 175K BTU and higher
Common causes of Rinnai code 681
- Bypass valve/servo misalignment
- Faulty or disconnected inlet thermistor
- Faulty or disconnected heat exchanger thermistor
A technician checks these and 2 other possible causes on site before replacing any part.
Rinnai models that use code 681
IP060160CIP090099CIP090160CIP090199CIP120199CIP150199CIP175199CIP199199C
Other Rinnai Combi Boiler codes
All Rinnai Combi Boiler error codes →
Rinnai code 681: homeowner questions
What does Rinnai code 681 mean?
DHW supply temperature abnormality. The measured bypass ratio, calculated from the inlet, heat exchanger and outlet thermistors, doesn't match the expected ratio — often from a misaligned bypass valve or a bad temperature reading.
Is it safe to keep using my combi boiler with code 681?
It depends on the cause. This is often caused by something simple. Try the safe checks below; if the code returns, book a service call before it turns into a no-heat or no-hot-water emergency.
Can I reset Rinnai code 681 myself?
You can try one reset (power off for 30 seconds, then on). If Rinnai code 681 comes back, the cause is still there and a licensed technician should check it.
Who can fix Rinnai code 681 near me?
Aurora Star Tech Inc. repairs Rinnai combi boilers in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.
Homeowner help: Tankless Water Heater No Hot Water: What to Check · Boiler Not Heating: What to Check
Source: Rinnai Troubleshooting I-Series Plus Boiler Diagnostic Codes (800000375), p.38. Written in our own words as a summary; always check the original manual.
General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.