Weil mclain ultra error code e-02

E02 indicates an ignition problem, which results in the burner not lighting.

Not unlikely, the ignition electrode is faulty and needs to be replaced.

The flame signal is poor, while the burner is functional. Replace the ignition electrode.

Make sure that the burner is clean and gas pressure is optimal. Use a manometer. Make sure the boiler is grounded properly, and all connections are ok.

If you find none of these, most likely, the control module is faulty.