OK.....
ECO opening is a real long shot.
If it was opening early it would continue to do so.
2 nights of use and 1 non-relight.
That could be spark electrode position....has to be directly in flame (tip should get RED) and gap set at 1/8"
That could be ground issue.......either at spark electrode assembly (bracket/mount screw not tight/clean contact)
That could be loose spade/terminal contact on t-stat/ECO
That could be connector contact issue at circuit board
That could be gas solenoid terminal/spade contact issue
That could be a fluke
Poor or corroded wire connections cause most of the intermittent problems in water heaters.
And no grease or dielectric sprays etc.
T-stat and ECO must make clean constant direct contact with tank wall.
Terminals on the t-stat/ECO should not move and wire spade connectors should go on the terminals tight.
1 non-fire is not a real issue.....if it continues to not fire up --- that is an issue
