Honeywell T8401C, Product Data

PRODUCT DATA

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68-0180-3

T8400C, T8401C and T8424C,D

Electronic Thermostats

APPLICATION

The T8400C and T8401C Standard Electronic Thermostats 

provide single-stage, non-programmable temperature control 

for 24V heating-cooling systems with manual changeover 
from heat to cool.

The T8424C Electronic Multistage Thermostat provides two-
stage heat and one-stage cool control.

The T8424D Electronic Multistage Thermostat provides two-
stage heat and two-stage cool control.

FEATURES

• Attractive styling complements any decor to the 

homeowner’s delight.

• Ease-of-use means fewer homeowner questions and 

increased homeowner satisfaction.

• Large display for quick easy readability.
• Conveniently sized 3-1/2 x 3-1/2 thermostat with 

optional decorator cover plates (3-7/8 in. x 3-7/8 in. and 

5-3/4 in. x 5-3/4 in.) makes it easy to install in a variety 
of locations.

• Keys are located for easy access.
• Fan and system switches are located on the lower 

edge to eliminate accidental setting changes.

• Easy installation, setup and self-test saves time and 

increases installer productivity.

• Manual changeover from heat to cool eliminates 

unexpected system operation.

• °F or °C temperature display for added model 

flexibility.

• Selectable heating cycle rate (1, 3, 4, 5, 6 or 9, 12 cph) 

for a variety of applications which reduces the amount 
of inventory. 

• Cooling cycle rate is fixed (3 cph), the standard setting 

for compressors, for speedy installation.

• Setpoints are permanently held in memory (no 

batteries used) and retained during power outages for 
increased installer and homeowner convenience.

• Power stealing and hard wired models available for 

virtually all equipment and application needs including 

gravity or radiating systems, hydronic heat, 
condensing gas furnaces, gas or oil forced air and 

electric heat.

T8400C and 

T8401C

T8424C,D

Contents

Application ........................................................................

1

Features ...........................................................................

1

Specifications ...................................................................

2

Ordering Information  ........................................................

2

Installation ........................................................................

3

Settings and Adjustments .................................................

8

Operation .......................................................................... 10
Checkout .......................................................................... 12

Troubleshooting ................................................................ 13