Bosch Error Code E9: Safety high limit or flue gas limiter tripped (Boiler)
Bosch error code E9 on a boiler means: Safety high limit or flue gas limiter tripped. It is also called Bosch diagnostic code E9.
Homeowner? What Bosch code E9 means for you
Call a technician Your boiler is reporting: Safety high limit or flue gas limiter tripped. The boiler has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.
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 E9 mean?
A heat exchanger safety limit or the flue gas temperature limiter has opened. The same code is used when the pump has seized.
Applies to: Bosch Greenstar ZBR 21/28/35/42-3A boilers and ZWB 28/35/42-3A combi boilers
Common causes of Bosch code E9
- Faulty limiter or wiring
- Low system pressure or trapped air
- Pump capacitor weak or pump seized
A technician checks these and 2 other possible causes on site before replacing any part.
Bosch models that use code E9
ZBR21-3AZBR28-3AZBR35-3AZBR42-3A
Other Bosch Boiler codes
All Bosch Boiler error codes →
Bosch code E9: homeowner questions
What does Bosch code E9 mean?
Safety high limit or flue gas limiter tripped. A heat exchanger safety limit or the flue gas temperature limiter has opened. The same code is used when the pump has seized.
Is it safe to keep using my boiler with code E9?
It depends on the cause. The boiler has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.
Can I reset Bosch code E9 myself?
You can try one reset (power off for 30 seconds, then on). If Bosch code E9 comes back, the cause is still there and a licensed technician should check it.
Who can fix Bosch code E9 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
Source: Bosch Greenstar ZBR/ZWB 21-42-3A service manual 6721853955 (2025-11), Table 38 Faults shown on the display, p.74-75; Greenstar combi 100 p/151 p service manual 6721853953 (2025-11), Table 33. 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.