Wrap your outdoor plastic condensate pipe in weatherproof lagging to prevent freezing during cold winter snaps.
If your Viessmann boiler is under 8 years old, repairing the D6 error (even a new PCB) is almost always worthwhile.
In rare cases, the main control board fails to send voltage to the fan. Step-by-Step Troubleshooting Guide
The error reads as a "Flow Switch D6" or "Strömungssensor" fault . This means the internal flow rate has dropped below the minimum threshold required to safely operate the compressor or electric booster heaters. viessmann d6 error
If you've tried the troubleshooting steps above and the D6 error code persists, it's recommended to contact a qualified heating engineer or a Viessmann authorized service technician. They will be able to diagnose the issue and perform any necessary repairs.
The Viessmann D6 error code indicates a maximum pressure switch fault, meaning your boiler's internal pressure sensor detects that water pressure has exceeded safe operating limits (typically above 3.0 bar). When this happens, the boiler shuts down into a hard lockout state to prevent internal leaks, cracked heat exchangers, or component failure. What Does the D6 Error Code Mean?
Page 1 * Please file in Service Binder. * 5792 846 - 02 04/2025. * Part number: 7828749 Flow Sensor. for use with: Vitodens 100-W, Viessmann US Viessmann Fault Codes - FREE BOILER MANUALS Wrap your outdoor plastic condensate pipe in weatherproof
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Open all radiator thermostatic valves to ensure water isn't dead-heading. Restores required minimum circulation.
The fan motor may be burnt out, jammed with debris, or suffering from worn bearings. Step-by-Step Troubleshooting Guide The error reads as a
Preventing the D6 error in the future is best achieved through a mandatory annual boiler service. During a service, an engineer will proactively check the charge of your expansion vessel and ensure all safety switches are operating perfectly before winter begins. To help diagnose this further, let me know: What is the of your Viessmann boiler?
Your heating system requires a specific water pressure to operate (usually between 1.0 and 2.0 bar). If the pressure is too low, the circulation pump cannot maintain an adequate flow rate.
The ionisation electrode sits next to the burner flame. It detects the heat and electrical conductivity of the fire to confirm a flame is present. Over time, this metal probe can develop carbon buildup, rust, or warp out of shape, preventing it from sending a clear signal to the control unit. 2. Defective Burner Control Unit
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The fan motor may have burned out, or the bearings might be seized, preventing the blades from spinning.