As for the heat only being lukewarm, the monovalve may be the culprit. It's easy to access, easy to bypass for testing purposes, easy and relatively inexpensive to replace. It is simply a solenoid with the current controlled by the temp wheel in your CCU. If you remove the solenoid (inside the monovalve), then the heat will be full tilt all the time. If you pull the solenoid and get max heat, then you know the monovalve is not functioning properly. Given that you do this and have heat, then the problem is either the monovalve is getting an electrical signal and does not open (a solenoid problem) or the monovalve is not getting an electrical signal (a CCU problem)

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John Schroader
bio burnin' 83 300D, '83 300 SD, '79 240D
"I've never met a man who was good at making excuses who was good at anything else" Ben Franklin
"You cannot permanently help a man by doing for him what he could and should do for himself" Abraham Lincoln