[rheavn]

It has come to my attention that I missed one step that I wasn't aware of when I performed my annual service. The mixing valve needs to be exercised annually. It sits directly under the burner unit, hence the need to do it during service when you already have the burner unit out. The valve has a plastic round knob that I could touch, but not turn without removing the burner. To exercise the mixing valve mark the knob, turn as far as it will go in both directions and then return the knob to the original position. If the valve knob will not turn then the valve is bad and needs to be replaced. The good news is that you can replace just the guts. I'll post a couple of pictures that I got off Roger Burke's web site-http://forum.rvhydronicheaterrepair.com/forum.php