Boiler is not responding to a call for heat

Symptoms:

Boiler is not responding to a call for heat (the burner does not fire at all), no fault is displayed on the boiler control, and coding address "38" has a value of "33".

Cause:

The internal, non-replaceable fuse in the boiler control console has failed.

This can be caused by:

1. An electrical short at the gas valve terminals, if they have become wet. Burning or discoloration of the terminals will usually accompany this failure.

2. A faulty gas valve or radial fan.

3. An internal fault within the control.

Resolution:

Viessmann recommends that the control console, coding card and gas valve be replaced as a group, to prevent one faulty component from damaging others.

In addition:

1. If there was an electrical short at the gas valve terminals, then the gas valve wiring harness must be replaced.

2. Check if the radial fan is faulty, and replace it if necessary.

3. Check if any other outside influences are negatively affecting the control.