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Viessmann 100, F4 fault on warm days (in USA)

Discussion in 'Plumbing and Central Heating' started by Ron Graff, 30 Mar 2020.

  1. Ron Graff

    Ron Graff

    30 Mar 2020
    Thanks Received:
    United States
    I have a problem with my Viessmann Vitodens 100 WB1B-26 boiler. It has had this problem since it was installed (Dec 2012), but is worse this year due to the very warm winter in my area. The problem goes like this. From midnight to 10 AM, the boiler works fine. But when the outside temperature gets up to 45-50 deg F, heat is not needed since the house is warm so the boiler stays off and cools down. Then about 7 PM after the sun goes down, the outside temp is colder, and the boiler should turn on, but the F4 fault occurs instead. Once a day in the evening, I reset the boiler (power off then on), the boiler whines for a few seconds then stops, there is a thump, and the boiler turns on. Everything is fine for the rest of the evening and morning of the next day. Then at 7 PM, it goes thru the cycle again.

    During the winter months when the boiler never gets cold, everything works great.

    Any help is appreciated. Thanks Ron

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