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Optimal Support Tool
Navigate using the tabs below to explore troubleshooting, product specs, and setup guides. All content is sourced from official Optimal documentation and firmware specs.
Quick access
Troubleshooting
Guided decision tree to diagnosis
Error decoder
Decode any error code including E096 and E128
Repair guides
Step-by-step with images
Reference
Diagnostics d-01 to d-21, LED colors
WiFi Setup
Connect your unit to home WiFi
Product lineup
12kW
opti12 / opti12+
$499 / $599
15kW
opti15 / opti15+
$519 / $619
18kW
opti18 / opti18+
$629 / $729
27kW
opti27 / opti27+
$729 / $829
Troubleshooting guide
Guided diagnosis for common symptoms, step by step.
Error code decoder
Enter the number after E on the display. Stacked codes like E096 are automatically decoded.
E
Common codes:
E001E002E004E008E016E032E064E096E036E048E128E160E255
Repair guides
Step-by-step part replacement guides with images from official Optimal documentation.
Part replacement
Heating element
8-step full replacement
Thermostat
Thermal paste, wire routing
Control board
5-wire transfer, WiFi board
Power board
TRIAC, thermal paste, wire order
WiFi board
10-pin connector, app setup
Annual maintenance
Scale inhibitor and vinegar flush
Reference guide
Diagnostic codes and LED indicator.
How to use the diagnostic menu: Press the diagnostic button (the sliders icon) on the control panel to enter diagnostic mode (LED turns teal). Use the up and down arrows to scroll between diagnostic codes (d-01, d-07, etc.), then press the diagnostic button again to view the reading. Press the power button once to exit the diagnostic menu.
Diagnostic codes
| Code | Name | Details |
|---|---|---|
| d-01 | Flow rate | Incoming GPM (mGPM / 10) - read-only Min 0.25 GPM to activate. Use to verify flow is reaching the unit. |
| d-02 | Voltage | Input voltage in volts - read-only Must be 200V+. Use to diagnose E016. Check each circuit. |
| d-03 | Input temp | Incoming cold water temperature - read-only |
| d-04 | Output temp | Outgoing hot water temperature - read-only Watch for temp climbing above set point - indicates E064 overshoot. |
| d-05 | Heating power | Actual heating power in W / 10 - read-only |
| d-06 | Heat capacity | Max heat capacity in W / 10 - read-only |
| d-07 | Flow capacity | Max GPM at current set temp - read-only If d-01 is greater than d-07, unit is undersized for current demand. |
| d-08 | Heater calibration | Baseline: 100. Normal range: 90–100. Below 85 = possible flow issue. Above 150 = possible calcium buildup. The unit is working harder to heat through scale. Check local water hardness to determine flush frequency. After flushing, unit should reach set temperature or within 2°F. Read-only. |
| d-09 | Zero calibration | 0=pending, 1=done, 2=factory default Change 1 to 0 to force recalibration. Change 1 to 2 to reset to factory. Do not change without support guidance. |
| d-10 | AC cycles | Input frequency in Hz - should be 60Hz in US - read-only |
| d-11 | Model | Rated kW (12, 15, 18, or 27) - read-only |
| d-12 | Build version | Major x 1000 + Minor x 100 + Decimal - read-only |
| d-13 | Circuits | Number of heating circuits / elements - read-only |
| d-14 | Ignore output temp | 1 = unit ignores output temp for calibration Temporary E064 workaround. Do not change without support guidance. |
| d-15 | Freeze protect | 1=enabled, 0=disabled - adjustable Must stay enabled for installs in spaces subject to freezing. |
| d-16 | Vacation mode | 1=enabled, 0=disabled - adjustable When enabled, LED shows purple and unit will not heat. |
| d-17 | Heater error word | Per-circuit error breakdown - read-only Bits 0-3: Heat Error Circuits 1-4. Bits 4-7: Thermostat Error Circuits 1-4. |
| d-18 | Sensor error word | Per-sensor error breakdown - read-only Bit 0: Transducer Left. Bit 1: Transducer Right. Bit 4: Thermistor In. Bit 5: Thermistor Out. |
| d-19 | Heater status word | Live heater status flags - read-only Bit 0: Heaters on. Bit 4: Maxed out. Bit 5: Vacation mode. Bit 6: Freeze protect active. |
| d-20 | Clear errors / reset | Enter value then press diagnostic to execute: 1=reset WiFi. 3=clear all errors. 5=reset user config. 7=restart unit. |
| d-21 | Temp units | Degrees F or C - change value to toggle |
LED power indicator - top right corner of control panel
Blue
Power is running to the heater, but it is in "off" mode. Water will not heat.
Push the power button to turn it on.
Green
Power is running, the heater is on and ready to heat when hot water is running.
White
Power is running and the elements are actively heating.
Red
An error code has been detected.
Use the Error Decoder tab with the code shown on the display.
Teal
The heater is in diagnostic mode.
Press the power button to exit.
No light (digits still on)
The output temperature is not reaching the set temperature. This means the flow rate is too high.
Reduce flow, lower set temp, or check d-07 vs d-01.
Purple
Vacation mode is active. The unit will not heat.
Disable via the app, or navigate to d-16 and set the value to 0.
Entire display off
No power reaching the unit. If both the temperature display and the upper-right indicator are dark, the LCD is not powered.
Check all breakers are on. If breakers are on, the small fuse on the power board that powers the LED control board may be blown. Contact Optimal support.
Model specs
Electrical specifications from official Optimal installation manuals
opti12
opti15
opti18
opti27
Warranty
Coverage terms, how to file a claim, and what's excluded.
Residential
25
years
Commercial
5
years
Covers the heat exchanger and all component parts against defects in materials and workmanship under normal use. Optimal° will repair or replace defective parts at its option.
Warranty is effective from the original invoice date. Optimal° covers ground shipping both ways within the continental US for warranty claims.
Labor, reinstallation, and associated costs are not covered. These are the responsibility of the end user.
How to make a claim
First register your unit, then contact the Optimal° support team:
What's not covered
Tap to view (13)
This warranty does not cover failures or damages caused by:
- ✗Failure to install per applicable building codes or electrical trade practices
- ✗Improper installation or failure to operate and maintain per manufacturer instructions
- ✗Improper sizing of the unit for the application
- ✗Abuse, accident, fire, flood, freeze, lightning, or acts of God
- ✗Operating in a corrosive or contaminated atmosphere
- ✗Dry firing: operating with an empty or partially empty heat exchanger
- ✗Hard water / calcium or scale buildup (calcification or electrolysis)
- ✗Operating above the pressure shown on the rating label
- ✗Use of unauthorized replacement parts or attachments
- ✗Unit purchased from an unauthorized reseller
- ✗Unauthorized parts installed after purchase
- ✗Unit removed from its original installation location
- ✗Rating label has been removed
Note: Warranty compensation is subject to validation by Optimal° claims department. Each warranty replacement must be returned to Optimal° within 30 days or the full MSRP may be charged to the card on file.
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Request a warranty part: Thermostat
Fill out this form and we'll email the request to Optimal° support. An agent will confirm warranty status and ship the part on the next business day. You will not be charged for warranty-covered parts.
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How to use the diagnostic menu
The diagnostic menu shows real-time readings from your Optimal° heater: things like flow rate, temperature, and heater calibration. Codes are labelled d-01, d-04, d-07, etc.
- 1Locate the diagnostic button on the control panel: it's the icon that looks like three small sliders, on the bottom right of the LED display.
- 2Press it once. The display will show d-01 (your current flow rate).
- 3Use the up and down arrows on the control panel to scroll to the code you need (d-04, d-07, d-08, etc.).
- 4When you're on the code you want, press the diagnostic button again to see the reading.
- 5To exit diagnostic mode, press the power button once.