How to Wire the Inkbird ITC-308 for Cold Plunge (Complete Guide)

The Inkbird ITC-308: the DIY cold plunge's brain

The Inkbird ITC-308 is the temperature controller that runs most DIY cold plunges. It's a $35 dual-stage thermostat that controls both heating and cooling equipment — for cold plunge use, you'll only use the cooling side. The ITC-308 turns your chiller (or chest freezer) on and off to maintain your target water temperature within ±1°F.

This guide walks through complete wiring, configuration, and calibration.

What's in the box

The Inkbird ITC-308 ships with:

• The controller unit itself (with LCD display and 4 buttons)
• A waterproof NTC temperature probe (6-foot cable)
• Two AC outlets: one labeled "Heating" (red), one labeled "Cooling" (blue)
• A power cord (plugs into standard US outlet)
• An audible alarm for sensor fault or out-of-range temps

Wiring setup (3 connections)

Step 1: Plug the Inkbird into a GFCI outlet

This is non-negotiable. The Inkbird controls a high-current appliance (chiller or freezer) near water. A ground fault without GFCI protection is potentially fatal. If your outlet isn't GFCI, replace it before proceeding (or use an inline GFCI adapter, $15 on Amazon).

Step 2: Plug your chiller into the "Cooling" outlet

The Inkbird has two outlets — red "Heating" and blue "Cooling." For cold plunge use, plug your chiller (or chest freezer) into the blue "Cooling" outlet. The Heating outlet stays empty (unless you're running a heated tub for contrast therapy).

Verify your chiller's power draw doesn't exceed 10 amps (1100W at 110V). Most 1/2 HP chillers draw 5–7 amps. If you're running a 1+ HP chiller, check the spec sheet — you may need a heavy-duty relay.

Step 3: Drop the probe into your plunge water

The waterproof NTC probe goes into your plunge water. Mount it at mid-depth (about 12" below the surface for a typical plunge), away from the chiller's return jet. The return jet water is colder than the rest of the tub — if the probe sits there, your controller will read artificially low and your chiller won't run enough.

Use the included suction cup mount or tape the probe to the inside wall of your tub. Route the cable above the waterline — don't let it dangle where it could get pinched or cut.

Configuration (5 settings)

Once everything is plugged in, configure the ITC-308's settings. Press and hold the "Set" button for 3 seconds to enter configuration mode. Use the up/down arrows to navigate, press Set to confirm each setting.

Calibration

The ITC-308's probe is accurate to ±1°F out of the box, but you should verify against a floating pool thermometer. If the readings differ by more than 1°F, adjust the CA (calibration) setting to match the thermometer.

For example: if your ITC-308 reads 47°F and your floating thermometer reads 45°F, set CA to -2. The ITC-308 will now display 45°F and your chiller will target the correct temperature.

Troubleshooting common issues

Issue: Chiller not running

• Verify the ITC-308 is plugged in and the screen is on
• Check that current water temp is above your SET temperature (chiller only runs when water is warmer than target)
• Verify the compressor delay (PT) hasn't just elapsed — wait 3 minutes
• Check the alarm status — sensor fault will disable the cooling outlet

Issue: Chiller runs constantly but water won't cool

• Your chiller may be undersized — see our chiller sizing guide
• Check for air in the chiller loop (bleed air from the highest point)
• Clean the chiller's condenser coils — dust buildup kills efficiency
• Verify the probe is reading true water temp, not chiller output temp

Issue: Temperature overshoots target

• Increase the compressor delay (PT) to 5 minutes
• Move the probe closer to the chiller return (it will react faster)
• Check that your chiller has a built-in thermostat — if so, set the chiller's thermostat 2°F below the ITC-308's setpoint so they don't fight each other

Issue: Alarm sounds continuously

• Check the display for "HH" (sensor disconnected) or "LL" (sensor shorted)
• Verify the probe cable isn't pinched or cut
• Replace the probe if damaged (Inkbird sells replacements for $10)