How to Fix / Troubleshooting

Safety: Turn off power and gas. Only licensed gas technicians should work on gas valves.

Inspect gas valve connections: Check the electrical connector to the modulating gas valve coil. Ensure it is fully seated and free of corrosion.
Check wiring harness: Inspect the harness from the control board to the gas valve for damage.
Gas valve test: A qualified technician should measure the modulation signal and verify that the gas valve responds correctly, adjusting manifold pressure as per Buderus specifications.
Replace gas valve if faulty: If the valve does not respond or is out of calibration, replace it with an identical Buderus-approved valve and perform combustion analysis.
Control board check: If the valve is good but no modulation signal is present, the control board may need replacement.
Recommission and test: After any gas valve work, perform a full safety and combustion check before returning the heater to service.

Error H71; heater may not modulate correctly or may shut down.

Possible Causes