Bosch Error Code Display off: Display dark – appliance switched off (Boiler)
Bosch error code Display off on a boiler means: Display dark - appliance switched off. It is also called Bosch diagnostic code Display off.
Homeowner? What Bosch code Display off means for you
Usually minor Your boiler is reporting: Display dark - appliance switched off. This code is usually informational or minor. The safe checks below often clear it; call us if it keeps showing up.
Safe things you can check yourself
- Check the thermostat: right mode (Heat or Cool), set a few degrees past room temperature, and fresh batteries if it uses them.
- Make sure the unit has power: its on/off switch (often looks like a light switch near the unit) is ON and the breaker in the electrical panel is not tripped.
- Look at the pressure gauge on the boiler. If it reads much lower than usual or near zero, or water is leaking, call a technician.
- Outside, make sure the intake and exhaust pipes or vent cap are not blocked by snow, ice, leaves or a nest.
- Check that the boiler gas valve is open (handle in line with the pipe).
- Try one reset: turn the power off for 30 seconds, then back on. If the code comes back, stop resetting and call a technician.
Call (647) 657-2977Book a service call
Licensed technicians serving Vaughan, Toronto and the GTA.
What does Bosch error code Display off mean?
When the ON/OFF switch is turned off the display goes dark. When it is switched on the display shows the supply temperature again. On the very first power-up the boiler also runs a one-time purge in which the heating pump cycles on and off for about 4 minutes.
Applies to: Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis
Bosch models that use code Display off
ZBR21-3AZBR28-3AZBR35-3AZBR42-3A
Other Bosch Boiler codes
All Bosch Boiler error codes →
Bosch code Display off: homeowner questions
What does Bosch code Display off mean?
Display dark - appliance switched off. When the ON/OFF switch is turned off the display goes dark. When it is switched on the display shows the supply temperature again. On the very first power-up the boiler also runs a one-time purge in which the heating pump cycles on and…
Is it safe to keep using my boiler with code Display off?
Usually yes. Code Display off is normally minor, but if it keeps coming back have it checked.
Can I reset Bosch code Display off myself?
You can try one reset (power off for 30 seconds, then on). If Bosch code Display off comes back, the cause is still there and a licensed technician should check it.
Who can fix Bosch code Display off near me?
Aurora Star Tech Inc. repairs Bosch boilers in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.
Homeowner help: Boiler Not Heating: What to Check
Troubleshooting guides
- No heat or some zones cold All brands · Boiler
- Force minimum or maximum output for 15 minutes (function 2.F) Bosch · Boiler
- Lock or unlock the key pad Bosch · Boiler
- Lock the boiler at minimum or maximum output (function 9.A) Bosch · Boiler
- Move the 3-way valve to centre to drain (function 7.b) Bosch · Boiler
- Open the service functions (Greenstar service button) Bosch · Boiler
- Read the latest stored fault code (function 6.A) Bosch · Boiler
- Reset the service-due indication (function 5.A) Bosch · Boiler
- Restore factory settings (function 8.E) Bosch · Boiler
- Start or stop the building drying program (function 7.E) Bosch · Boiler
- Start the air-purge routine (function 2.C) Bosch · Boiler
- Start the emissions test (chimney sweep) mode Bosch · Boiler
- Test ignition with continuous sparking (function 8.F) Bosch · Boiler
Source: Bosch Greenstar wall ZBR-ZWB 21-42-3A service 6721853955 (2025-11) (same content in combi service 6721853953), 8.2 Switching the appliance ON/OFF p.49. Written in our own words as a summary; always check the original manual.
General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.