Red light on > Atwood water heater

The Red Light is letting you know that at some time the Water heater DID NOT light when called for. Once that happens, the system is locked out and you must turn it OFF like you did, and restart. Doug

There may be two lights.. You mentioned "The red light on the switch"
On my water heater the switch lit up red if turned on.. That way you knew if Gas or Electric was on) then there was a FAULT light (All red)

The RED fault light... Indicates one of two conditions.
ONE Over temp (Emergency Cut Out) sensor activated (See notes) That's on any mode.

Two Flame not detected after 3 tries to light (Gas only)

NOTES. The ECO is a disc thermostat I think it's like 190 or 200 degrees.
But the wires going to it can "Tarnish" and lose connection.. So it might be over temp.. Or broken wire, or bad connection Or control board failure or _________ (Fill in the blank).