Purchased a Weil-McLain Ultra 230 Hot Water Boiler Natural Gas about a yr ago.
From basically day 1 have had lockouts. In the 30-50 range over a course of weeks. Now down to 18. Reason: Return temp exceeded the supply temp. Have had numerous visits from Weil Mclain people and people that installed the heater. They can't find a reason. What would be reasoning for the return temp. to exceed the supply temp.

I would first start by testing the sensor(s) since when they go bad or out of range problems like what you are having come up. There should be a ohm value stated in the master repair/service manual for your unit that came with the unit. If not go to there web site and download it.