Viessmann Vitodens 100-W, BIKA 35, heat and hot water combi. This was installed in 2017 (9 years old) and has worked perfectly every winter for heating and hot water. This summer it went into F4 and would not reset. The issue has not been resolved although a replacement main Fan was installed, and a new gas valve was tried. If you can resolve this or use for parts you have a great deal here. Currently set for propane can be converted to NG. email or text ok, five 1 eight- 9 two-8-7 nine six four.