We have this heater (unfortunately) (gas)
For 3 years we replaced thermocouplers, pilot assembly... everything. Still had periods where we had to re-light the unit several times a day.
Finally.. we now have the fix and have not had to re-light this unit for 6 months. It is working like a champ. All we did was remove the little glass pane at the bottom. That is it... no more.
When the heater was firing and getting hot, it was starved for air. Now that is not a problem now.
It did not hurt to have a master plumber for a father-in-law. Just took time to finally figure out what was going on.