Honeywell T8570 User Manual

Heating Setpoint 

Cooling Setpoint 

Description 

Default 

Range 

Default 

Range 

°C Scale 

18°C 

10-18°C 

25°C 

25-30°C 

°F Scale 

65°F 

50-65°F 

77°F 

77-90°F 

FAN SPEED SWITCH (SP3T LINE VOLTAGE) 
Where supplied, the fan switch allows the selection of three 

different settings: low, medium, or high. 

NOTE:  The installer should select Constant Fan mode if the 

fan motor is a type that does not start reliably at low 

speed. 

SYSTEM HEAT/COOL SWITCH (SPST LOW VOLTAGE) 
Where supplied, this switch signals the microprocessor to 

operate the relays in either heating or cooling mode: In heating 

mode, the cooling relay is disabled. In cooling mode, the 

heating relay is disabled. 

TEMPERATURE (COMFORT) SETPOINT 
The temperature setpoint can be adjusted between 10°C and 

30°C in steps of 0.5°C by using the [UP] and [DOWN] keys. If 

°F is set within the installer setup mode (see later), the range 

will be 50°F to 90°F, adjustable in 1°F steps. 

DISPLAY 
The measured room temperature is normally displayed (unless 

rt = 0 in the installer setup mode), and the first press of the 

[UP] or [DOWN] keys will switch to display the user setpoint. If 

no key is pressed for 5 seconds, the display will return to 

showing the room temperature. 

When the cooling relay is closed, this will be indicated by a 

(snowflake) symbol, whereas closure of the heating relay will 

be indicated by a (flame) symbol. 

If there is a wiring problem or the room temperature is less 

than 5°C (40°F) or over 38°C (100°F) the display will return a 

SF (Sensor Failure) warning. If this warning is not due to a 

wiring problem it will disappear once the remote sensor or 

thermostat comes within the 4.5 to 37.8°C (40 to 100°F) range. 

If the SF warning is due to a faulty remote sensor connection 

the thermostat will not transfer measurement to the internal 

sensor. To resolve the faulty connection the thermostat must 

be powered down, the remote sensor connection must be 

removed or fixed and then the thermostat must be re-powered. 

The thermostat allows many of its operating parameters to be 

adjusted via an Installer Setup Mode. Each operating 

parameter has a two-letter identifier code, which is shown on 

the display during the Installer Setup Mode programming 

sequence. A description of these is shown in Table 5. 

PROGRAMMING PARAMETERS 
The installer setup mode is accessed by reducing the setpoint 

to 10°C (50°F), waiting 3 seconds or until the room 

temperature is displayed, and then pressing the [UP] and 

[DOWN] keys simultaneously for 3 seconds. 

The first parameter identifier will be displayed at this point and 

the parameter value can be changed by pressing the [UP] key. 

The first press displays the default value and any subsequent 

press alters the value. The values will wrap around. 

To select the parameter value and move to the next parameter, 

press [DOWN]. After the final parameter is selected, a further 

press of the [DOWN] key will exit from the programming mode. 

PARAMETER VALUES 
Each parameter has a default value that is used when the 

thermostat is first powered up. This value can be changed from 

within the Installer Setup Mode, and once changed, it will be 

stored in the EEPROM so it is not lost in the event of power 

interruption. 

If the user wishes to restore the parameters to the default 

values, this can be done by changing the temperature scale tS 

from °C to °F (or °F to °C) and back again. 

PROGRAMMING EXAMPLE 
To enter the installer setup mode: 

1.   Press to change the temperature setpoint to 10°C  

(50°F).  

2.   Wait 3 seconds, or until the room temperature is dis-

played. 

3.   Press and hold together until [tS] is displayed. 

4.   Press once to show the default Temperature Scale 

value. Continue to show all possible values of this 

parameter in sequence.  

5.   When the desired value is displayed, it is selected by 

pressing once. This will also move to the next parameter, 

whose identifier will now be displayed. 

6.   Continue to use to move from one parameter to the next, 

and to alter the parameter value. 

7.   When the last parameter [rt] has been selected, a final 

press of will return the display to its normal operating 

mode. 

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