Burner keeps going out in water heater..
Have changed coupler... cleaned burner
Flame is more intense at first but dies out
In 30 - 40 seconds... anyone?

Hi Josephine

Issue sounds exacly like a combustion/make-up air issue.

Most likey what you have here is a clogged filter... could be exterior to the unit, could be interior (honeycomb)... could also be a flame sensor (unlikely, but wanted to mention this).

Look around the base of the unit and maybe vacuum all around the exterior of the unit. If that doesn't make a change call the manufacturer of the water heater. All these water heater companies have websites and technical service departments that are very good at troubleshooting their specific products!

If you need anything beyond that just let us know, OK?

Mark