Brand: Honeywell
Category: Thermostat
Manual Type:
Language:
Manual for ST9400C - Troubleshooting and error codes + PDF Download
Uploaded: April 8, 2025, 1:56 p.m.
Manual Publish Date: 2007-01-01
Warranty Summary
No warranty information found in this manual.
The Honeywell ST9400C programmer provides timing control for central heating and hot water systems. It allows users to set ON and OFF periods to match their lifestyle.
Operating Modes:
- OFF: Heating remains off.
- AUTO: Heating switches ON/OFF based on the program.
- ONCE: Heating turns ON at the first ON time and OFF at the last OFF time.
- CONT: Heating remains continuously ON.
Override and Extra Hour Functions:
- OVERRIDE: Temporarily turns heating ON/OFF until the next programmed time.
- EXTRA HOUR: Extends heating for 1, 2, or 3 extra hours.
Troubleshooting and error codes
| Symptom | Possible Cause | Remedy |
|---|---|---|
| ST9400C has a blank LCD display | No power to the heating system | Check that there is power to the heating system |
| ST9400C has a blank LCD display | Fault in ST9400C | Call Installer |
| ST9400C indicates that Heating and/or Hot Water are ON, but radiators are cold and/ or taps are running with cold water. | Temperature controls are switched off or set too low | Check that the temperature controls in the system are set to appropriate levels |
| ST9400C indicates that Heating and/or Hot Water are ON, but radiators are cold and/ or taps are running with cold water. | Boiler or other system controls have malfunctioned | Call Installer |
| ST9400C shows the message 'INTERNAL FAULT' | Fault in ST9400C | Call Installer |
| When the slider is moved to the HOT WATER position, the display shows ‘NOT VALID' | ST9400C has been configured as a Mini-Programmer | Check the Contents page of this booklet or the 'Configuration & Service Data' section (page 18) to see if your ST9400C has been configured as a Mini-Programmer. Call Installer to check if this is correct for your heating system. |
Troubleshooting and error codes
| Symptom | Possible Cause | Remedy |
|---|---|---|
| ST9400C has a blank LCD display | No power to the heating system | Check that there is power to the heating system |
| ST9400C has a blank LCD display | Fault in ST9400C | Call Installer |
| ST9400C indicates that Heating and/or Hot Water are ON, but radiators are cold and/ or taps are running with cold water. | Temperature controls are switched off or set too low | Check that the temperature controls in the system are set to appropriate levels |
| ST9400C indicates that Heating and/or Hot Water are ON, but radiators are cold and/ or taps are running with cold water. | Boiler or other system controls have malfunctioned | Call Installer |
| ST9400C shows the message 'INTERNAL FAULT' | Fault in ST9400C | Call Installer |
| When the slider is moved to the HOT WATER position, the display shows ‘NOT VALID' | ST9400C has been configured as a Mini-Programmer | Check the Contents page of this booklet or the 'Configuration & Service Data' section (page 18) to see if your ST9400C has been configured as a Mini-Programmer. Call Installer to check if this is correct for your heating system. |