water heater not restarting

Remove all the electrical connects and burnish the contacts with a lead pencil eraser. Reconnect and pull off a couple of times before leaving seated. Blow out or vacuum any soot or debris. If this doesn't correct it, it probably needs a new circuit board.

It's NOT your t-stats cause if the ECO (high temp) t-stat OPENS you have to MANUALLY reset it via the Push to Reset Buttons in outside cover.
T-stats on Suburban are 130*F normal and 170*F on ECO
Turning ON/OFF switch off then back on only clears fault light on Suburban
(Will clear fault light on Atwood also but Atwood t-stats reset when temp cools off enough----the 140*F and 180*F are for Atwood t-stats)

Intermittent firing can be several things:

Does it spark and not light off?
Does it not spark at all?

Could be dirty connectors on circuit board....pull and clean contact surface on board with pencil eraser. Make sure pins in connector make good tight contact when reinstalling on board

Could be dirty spark electrode...clean with emery cloth to remove soot
Electrode needs to be directly in path of main flame and gap should be 1/8"
Check that high tension/voltage wire from board to electrode has clean tight connections
Clean and wipe down the ceramic on electrode with silicon ....if it is cracked it will track to ground

Burner tube needs to be aligned so that gas flows down center of tube (if crooked gas will bounce and air/fuel ratio gets disturbed) Flame spreader on end of tube needs to be parallel with tube so gas spreads out if fan.
Main orifice needs to be clear.remove from gas valve and clean by soaking in alcohol then blow air thru it

Check all ground connections......clean tight

Circuit board can be issue but that is usually NOT the issue with intermittent firing

Also check for dirt and debris and that your igniter is adjusted right.

Probably your thermostat. When the primary thermostat fails and the heater shuts off on the Emergency Cut Off (ECO) thermostat the circuit board locks out. You reset the circuit board when you turn it off and back on. Cheap fix. Both thermostats, under $20.00
Easy test. See if your water seems exceptionally hot at the end of the heating cycle. Primary stat 140º. ECO stat 180º.

Richard

Ignition Control Board, most likely. Since it seems to reset, which a thermocouple or limit switch (thermostat) wouldn't do since they are temperature activated.