H27
Bosch
Heating Element Overtemperature / Dry-Fire Protection
Bosch electric tankless heater displays H27; the unit may shut down or not heat properly.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Insufficient water flow through the heater, air trapped in the heater, failed temperature limiter on the heating element, scaled internal passages.
How to Fix / Troubleshooting
Safety first: Turn OFF power at the breaker. Do not operate the heater without water flow.
- Verify water supply: Ensure inlet valves are fully open and household water pressure is adequate.
- Bleed air: Open several hot water taps to purge air from the system. Some models have a manual bleed screw; follow the manual if present.
- Clean inlet filter: Remove and rinse the inlet filter screen to restore full flow.
- Inspect temperature limiters: Many Bosch electric models have manual reset thermal cutouts on the heating elements. After cooling, press the reset buttons if accessible. If they trip repeatedly, investigate flow and scaling issues.
- Descale unit: If you have hard water, internal scaling can restrict flow. Follow Bosch instructions for descaling the electric heater.
- Professional service: Persistent H27 may indicate a failing heating element or control board that should be replaced by a technician.
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Repair Difficulty
Medium
3/5
Required Part
Heating Element Assembly
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