Had Sierra Air out to repair a furnace control unit board that went bad in November 2016. The tech who came out was knowledgeable and correctly diagnosed that the electronic board which controls the furnace had gone bad. Although the replacement part is around $100 on Amazon, I ended up paying around $700 which included the service call and the replacement part. Not necessarily unreasonable in the world of home repair mark ups (but certainly not a great deal). Fast forward to May 2018 and the “new” control unit went bad, so I had Sierra Air come out to replace it. They tell me that the service was done 17 months ago, so the part is 5 months out of warranty. I ask them to at least replace the faulty part at cost, but they refuse and charge me $691... that’s $592 for the $100 part and $89 for the service call. Absolutely no willingness to do the right thing for their customers or stand behind their work/products.