Technical Service Bulletin

Issue:  Burner is locked out with fault code F7

Applies to:  Vitodens 100, WB1A Series (all models)

Vitodens 100, WB1A

Important Disclaimer

The information in this bulletin is intended exclusively for licensed heating contractors, and is NOT intended for the end user. This material is NOT intended to take the place of the information contained in the manuals shipped with the product.

Use of this information by unqualified personnel may result in property damage, personal injury or death.

End users are asked to contact a qualified contractor for all installation and service work. If you need assistance finding a contractor in your area, contact your Viessmann Sales Representative, or use our Contractor Locator.

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Symptoms:

The burner is locked out, and fault code "F7" is displayed on the boiler control.

Boiler water pressure is 12 psig or greater, but the boiler controller is reading pressure lower than the permissible pressure, resulting in an F7 fault.


Cause:

Faulty pressure sensor, which could be caused by damage to the sensor harness or a bad connection at the harness.


Resolution:

Measure the voltage on X9 terminals 1 and 2 to see what the sensor is measuring for boiler pressure – review section "Testing the water pressure sensor" below for details. If the pressure reading is lower than the actual pressure, then replace the pressure sensor.

If the sensor harness is damaged, then replace the harness.

If the problem persists after replacement, then contact Viessmann for a sensor bypass kit.



Testing the water pressure sensor

The following image displays the X9 plug on the boiler control, as viewed from the front.

Measuring between terminals 1 and 2 will reveal the return voltage from the sensor transducer to the control – this voltage depends on the boiler pressure (see graph below).

Measuring between terminals 1 and 3 will reveal the voltage going to the sensor transducer from the control – normally this should be 5 VDC.

X9 plug on the WB1A boiler control (front view)

Pressure sensor graph


Viessmann Technical Services 

Bulletin ID:     TSB-001

Date issued:   Oct 3, 2016

Updated on:   Nov 28, 2017

Revision #:      02

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