weil-mclain cgi install

The heat exchanger was leaking on my old boiler, so I had a contractor install a weil-clain cgi-4 series 3 with a mixing valve. Take a look at the pictures and I would appreciate feedback. Thermometer on the return line is 80 degrees, which does not seem correct. Mixing valve is still factory set to 120; should I increase or decrease?

I am thinking about having the expansion tank moved to a support bracket; copper tubing appears to be sagging. Barely 2 months old and having an issue with the main burner not firing, but the pilot is lit. Noticed there appears to be a stain under the burner....