Technical Service Bulletin

Boiler will not switch to heating or DHW mode on Vitodens 100 B1KE-199

Applies to: Vitodens 100-W, B1KE Series (model B1KE-199)

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.

By hitting "Yes" below you confirm that you have read, understood and agree to this warning, that you are licensed and hold the current, appropriate licences to work on said equipment in the location and/or jurisdiction of installation.

No, I don't agree. Help me find a contractor


Vitodens 100 B1KE-199 reportedly will not switch to heating or DHW mode, creating a "no heat" or "no hot water" service call.

The boiler's internal diverting valve becomes 'stuck' in either the space heating or domestic hot water production position, and will not physically switch positions. The boiler display does show the correct current call for heat (space heating or domestic hot water production), but is unable to move the valve to this position.



The check valve (located near the plate heat exchanger) has created a vacuum condition in the boiler's internal piping, preventing the internal diverting valve from moving.



Remove and replace the check valve that is installed in the DHW flat plate heat exchanger. For details on how to do this, please see the following document and video:

Viessmann Technical Services


Bulletin ID:


Date issued:

December 18, 2023

Updated on:

December 18, 2023

Revision #:


How can we help?
How can we help?