Honeywell ST9400C


The Honeywell ST9400C is a programmable electronic heating control unit that is designed for controlling heating and hot water systems in domestic properties. The ST9400C is a popular choice for homeowners and installers due to its versatility and ease of use.

Some of the key features of the ST9400C include:

  1. 7-day programming – The unit allows you to set different heating and hot water schedules for each day of the week, providing flexibility and energy savings.
  2. Dual zone control – The ST9400C can control both heating and hot water, allowing you to set different temperatures for different zones within your property.
  3. Holiday mode – If you’re going away, the ST9400C can be set to holiday mode, ensuring that your heating and hot water are turned off while you’re away.
  4. LCD display – The ST9400C features a clear and easy-to-read display, making it simple to program and operate.
  5. Automatic summer/winter time change – The unit will automatically adjust for daylight savings time, making sure that your heating and hot water schedules are always accurate.

Overall, the Honeywell ST9400C is a reliable and user-friendly option for controlling your heating and hot water system.

How to operate

  1. Switch on the power supply to the ST9400C by turning on the electricity supply to the unit.
  2. To set the clock, press the ‘SET’ button and use the ‘+’ and ‘-‘ buttons to adjust the time to the correct hour and minute. Press the ‘SET’ button again to confirm.
  3. To set the heating and hot water schedule, press the ‘PROG’ button. You can then use the ‘+’ and ‘-‘ buttons to select the day of the week you want to program. Once you have selected the day, press ‘PROG’ again.
  4. Now you can set the ‘ON’ and ‘OFF’ times for the heating and hot water using the ‘+’ and ‘-‘ buttons. Once you have set the times, press ‘PROG’ to move onto the next time period.
  5. Repeat this process for each time period for each day of the week until you have set your complete schedule.
  6. Once you have set your schedule, you can use the ‘TEMP’ button to adjust the temperature settings for both heating and hot water. The ST9400C allows you to set different temperatures for different times of the day.
  7. If you need to override the schedule and turn the heating or hot water on outside of the programmed times, simply press the ‘ON/OFF’ button until the heating or hot water comes on. To turn it off again, press the ‘ON/OFF’ button again.
  8. To enter holiday mode, press and hold the ‘SET’ button for 5 seconds. The ST9400C will then switch to holiday mode, turning off the heating and hot water until you return and switch it back to normal mode.

That’s a basic overview of how to operate the Honeywell ST9400C. For more detailed instructions, you should refer to the user manual that came with your unit.


Technical information

Central heating control typeProgrammer
Heating system compatibilityAll boilers
Control operationDigital
Temperature rangeHeating 5°C and 30°C
Hot water 35°C and 80°C
Display typeDigital display
Hertz (Hz)Designed to operate on a 230V AC, 50Hz power supply.
Switch rating230V AC, 50Hz supply voltage
3A maximum current for volt-free contacts (e.g. used for controlling boilers or pumps)
230V AC, 3A maximum current for SPST (single pole single throw) contacts (e.g. used for controlling motorised valves).
It is important to note that the switch rating refers to the maximum current that can be safely handled by the switch. It is recommended to always check the specific requirements of your heating system and ensure that the ST9400C is appropriately rated for the application.
Max. load (Inductive)3A
Max. load (Resistive)3A
Power consumption10W
Dimensions99mm x 145mm x 35mm (H x W x D)
Battery backupprogrammer continues to operate in the event of a power outage. The backup battery is a non-replaceable, long-life lithium cell that is designed to last for the lifetime of the programmer.
The backup battery is used to maintain the clock and program settings during power outages, so that when the power is restored, the programmer will continue to operate based on the programmed settings. It is important to note that the backup battery is not designed to power the heating system itself, only the programmer.
If the backup battery fails or becomes depleted, the programmer will need to be reset and reprogrammed once power is restored. To avoid this, it is recommended to replace the programmer if the battery is low or if the battery warning indicator is displayed on the screen.
Programmer Voltage230V AC
Smart compatibilityNone
Terminal capacityTerminals accept 1mm² to 2 x 2.5mm² cables

User guide