Just when I'm starting to trust our GB142/24, the house feels cold and the display is flashing 3C/217. Although those codes do not appear in the manual, Buderus tells me it means a communication problem with the fan, the wiring, or the UBA. After resetting, the boiler runs fine for a year or two. Have you had a similar issue with a GB142? Also, there are numerous postings here regarding the need to mix glycol with the circulating water, but the manual is very emphatic that no additives should be used - what do you think? I follow the cleaning procedures in the manual and we're into our seventh year with the only hard failure having been one hot surface ignitor.