Buderus 142-24 hot water issues

lukewarm540

Unit is about 7 years old. Always had aquastat set to about 135* f so no scalding issues in past. Have DHW as an indirect using a Bradford-White SW250rl unit. Recently noticed DHW was unusually hot while showering and checked temp at faucet-170* f . Changed Aquastat to new Buderus unit and used copper shims to transmit tank temp back into sensor as directed.
Water temp is now down to about 150*f BUT dial on Buderus controls HAVE NEVER been accurate. Used to have it set to about 100, which gave my water about 135ish. Now have it set to 90*, which gives my about 150ish. Can't really go any lower.
Is there a way to recalibrate controls so the dial is closer to what actual temp in tank is?
I am planning on installing an anti scald valve ASAP but not really sure what has changed in the last few weeks to give me such issues.
Any insight is greatly appreciated.
Eric

GW

Eric I've never heard of a GB being that far off, may be a sendor wire issue. You could remove the sensor wire from the GB142 board, and ohm it out. There's a chart in the manual that tells you whether the ohm readings are good or not. You may just need a new sensor cable/wire. You just need to know the tank temp in order to be accurate. OR just pull the sensor out of the the tank, let it acclimate to the basement air, and check the ohms. If your sensor wire is good, then your GB is not translating the ohms properly, and that may mean a bigger expense to fix it.