Our's had a problem when it was new that you might check for. If you pushed the reset button, you hot hot water until you turned off the faucet. The next time you turned on the water....no hot water. Turned out to be a flow sensor that was bad. When I shut off the water, it would kick the reset. Took a part they ordered and about twenty minutes for them to fix.
2015 Legacy SR340 360RB
2014 Jeep Wrangler Unlimited Toad
Gigi, Poppy and Sadie Lady...On the road, but not full time!