This boiler is an earlier model installed in 2001. The boiler is going off at 120 degrees F and is always short cycling .
I checked gas pressure and it was 2.5" wc. I checked all safetys and high limit stat and found all ok. The dual acting hot surface ignitor/flame sensor was replaced several months ago. To check the HSI for the .6 microamps I need the special tool which i was told neither provided by Lennox or Dunkirk. I ran a time check on the boiler staying on to see if it was a temperature control issue. If I let the boiler run approaching 120F it short cycles. If I let the boiler watertemp cool down and then start it up it will run steady on until it reaches 120. I cannot see any temperature control to check other than the High limit control. How is this boiler water temp controlled and is this a temperature control problem or something else?