Bosch Error Code ECO button lit: ECO button lit – economy / alternating mode (Boiler)

Updated October 16, 2026 · by Aurora Star Tech Inc.

Bosch error code ECO button lit on a boiler means: ECO button lit - economy / alternating mode. It is also called Bosch diagnostic code ECO button lit.

Low severityBoilerBosch Greenstar

Homeowner? What Bosch code ECO button lit means for you

Usually minor Your boiler is reporting: ECO button lit - economy / alternating mode. 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) 657-2977 Book a service call

Licensed technicians serving Vaughan, Toronto and the GTA.

What does Bosch error code ECO button lit mean?

The ECO button light shows the mode chosen. On a combi (ZWB) lit means Economy mode: hot water is only made when a tap is drawn, and a quick open and close of a tap asks for hot water. Not lit is Comfort mode, where the boiler keeps the DHW at temperature. On a heating boiler with a DHW tank (ZBR) lit means alternating operation between heating and tank; not lit is DHW tank priority (default).

Applies to: Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis

Safety: Gas, electrical and refrigerant work must be done by a licensed technician. Turn off power and gas before servicing, never bypass a safety control, and always follow the manufacturer's manual for your exact model.

Bosch models that use code ECO button lit

ZBR21-3A ZBR28-3A ZBR35-3A ZBR42-3A

Other Bosch Boiler codes

Code	Meaning
DHW setpoint flashing	Set DHW temperature flashing on display
Display off	Display dark - appliance switched off
E2	Supply temperature sensor fault
E3	Additional supply temperature sensor fault
E9	Safety high limit or flue gas limiter tripped
EA	No flame detected
Emissions test button	Emissions test (chimney sweep) button
F0	Internal fault
F1	Internal data error
F7	Flame detected with burner off
FA	Flame detected after gas shut off
Fd	Reset button pressed by mistake

All Bosch Boiler error codes →

Bosch code ECO button lit: homeowner questions

What does Bosch code ECO button lit mean?

ECO button lit - economy / alternating mode. The ECO button light shows the mode chosen. On a combi (ZWB) lit means Economy mode: hot water is only made when a tap is drawn, and a quick open and close of a tap asks for hot water. Not lit is Comfort mode, where the boiler keeps the…

Is it safe to keep using my boiler with code ECO button lit?

Usually yes. Code ECO button lit is normally minor, but if it keeps coming back have it checked.

Can I reset Bosch code ECO button lit myself?

You can try one reset (power off for 30 seconds, then on). If Bosch code ECO button lit comes back, the cause is still there and a licensed technician should check it.

Who can fix Bosch code ECO button lit 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

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Read the latest stored fault code (function 6.A) Bosch · Boiler
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Restore factory settings (function 8.E) Bosch · Boiler
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Start the air-purge routine (function 2.C) Bosch · Boiler
Start the emissions test (chimney sweep) mode Bosch · Boiler
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Source: Bosch Greenstar wall ZBR-ZWB 21-42-3A service 6721853955 (2025-11) (same content in combi service 6721853953), 8.10 and 8.11 Setting the DHW temperature p.55-56. 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.