I have a Waterfurnace Primere open loop system that is about 16 years old. Overall it works pretty well. Over the past few years my output air temperature has dropped a few degrees each year. Right now I’m only getting about a 10 to 12 degree rise in air temperature, with a max output at about 80 degrees even on stage 2. My service guy suggested cleaning the water side heat exchanger by reticulating a mild acid solution. I did that and no change. I also cleaned the air side heat exchanger with a brush and vacuum, overall that looks good. The service guy checked the refrigeration and said that the charge looks good and the compressor seems fine. I have also checked the water input and output temperatures. My water input temp is about 49, and with the valves wide open the output temp is about 45. In the past I valved back the water so that the output temp was at lowest 35, assuming this was a waste of water to let the excess run out. Valving back the water did not change the output temp of the air. Even with the water running wide open the output temp never peaks much over 80. I also have the fan speeds set a bit below the manufacturer factory set up, so it does not appear to be an excess air problem.
I don’t have a ton of confidence in my service guy – he is not a bad guy, he just seems stumped and I don’t have any other options for service in the area I live (extreme northern Michigan). Any ideas?