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Brian, HVAC Technician
Category: HVAC
Satisfied Customers: 840
Experience:  OFTEC registered oil heating engineer and plumber.
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I have a Viessman Vitodens 100 Wb and I keep getting an A9

Customer Question

JA: Hi. What do you want help with?
Customer: I have a Viessman Vitodens 100 Wb and I keep getting an A9 error. I do noit have an OpenTherm device connected
JA: How old is the appliance? Have you gotten error messages before?
Customer: 5 years old. The errors are fairly recent; past 3 months
JA: Do you plan on doing the work yourself?
Customer: yes
JA: Anything else we should know to help you best?
Customer: I dont think so
Submitted: 9 months ago.
Category: HVAC
Expert:  HVAC Guru replied 9 months ago.

Hello, one minute while I get some information together.

Expert:  HVAC Guru replied 9 months ago.

Hello and thanks for using this service! If you are a JA Member I would like to personally thank you and welcome you back! I am Appliance Guru an extremely experienced tech on the site and I try to get to as many customers as I can. NOTE it takes time for me to type research and add links so please wait for me to respond back I can only do this so fast. Secondly, I do not know your skill level so please try and let me know if I am going beyond your knowledge or comfort zone thanks! I strive for a 5 star rating from everyone especially our JA members.


That means the limit inside the unit has opened, the one typically on the motor or housing is open inside the unit. You would have to take it apart and check the thermal limits for continuity and replace the one that is bad. They really do not sell the internal parts for that unit though so you may not be able to repair it.

All I ask is please use the Star Rating Link at the top of your page before leaving, that is the only way I am paid anything through the site and that will also get you a DIRECT LINK emailed to you to get back to me! are greatly appreciated so thank you very much for using this service. If you have any other questions just post back to me here anytime!

Customer: replied 9 months ago.
Hi,What limit are you talking about? The fixed high limit switch?
Customer: replied 9 months ago.
Is the the outside temperature sensor?
Customer: replied 9 months ago.
I have the manual open in front of me Vitodens 100W WB1B Installation and Service Instructions, open on poage 91.There is no OpenTherm connected to X21 pins 1 and 2.What sensor are you refrerrring to?
Customer: replied 9 months ago.
Are you still there?
Customer: replied 9 months ago.
are you going to answer me???
Customer: replied 9 months ago.
Hi,do I have to rate you before I get an answer? How can I do that?are you still there?Am I wasting my time?
Expert:  Brian replied 9 months ago.

Are you from the UK?

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