All last year the exiting water temp was either warm or barely warm. Some days the heater worked, other days it only put out very mild lukewarm water although the burner was on the whole time. All other aspects of the heater operation is fine.
I'm guessing the Unitherm Governor is the problem. Possibly the Internal Automatic By-Pass Valve? Water pressure is stable at about 18 psi according to the filter gauge.