I've got the Delta 262RB with the Furrion on demand water heater. I was having problems holding the temperature also. The thermostat was all over the place even at tempatures outside of the 95-124 degree range, but the water would only get warm enough to take a lukewarm shower. I called the dealer and talked to a tech. that tried to walk me through a few fixes that never worked. He did say something about having a mixer valve open. I didn't understand the what mixer valve at the time. I was also having a small water leak behind the city water hookup panel. I couldn't help thinking the two problems were related. This week while setting up to camp I connected the sprayer to the spray port with the mixer valve and connected to the city water then turned the water on. Water began coming out of the sprayer. What I had done when I de-winterized the water system I failed to close the hot and cold water valves on the spray port mixer. I closed the mixer valves and removed the sprayer and continued the setup. When I checked out the water heater operation it worked perfectly. No matter what temperature I set the thermostat it stayed on temp. Also the water leak behind the panel had disappeared. I don't understand why open mixer valves would would cause such problems but it appears it does, I hope this helps.
