heating problem 98 E320

See if you give me a hand with this one, I got a clue myself but I like to hear it from someone else. I have a customer with a 1998 W210 E320, he recently stopped going to the
dealer because a weird engine noise was mis diagnosed, the waterpump bearing was gone and caused a unbalanced vibration, the dealer did find this and changed the boot that seals the steering column to the chassis. Anyway I grabed the fan blade and found 2 inches of play back and forth. I changed the waterpump last week, problem went away, but the customer called back complaining about no heat. He came back a day later, I found the same no heat, but if you select "HI" or "defrost" the heat works fine, so I checked for a unwanted pulse at the mono valve, sure enough, there is a voltage signal when there shouldn't be one, and off course you unplug the monovale and heat workes great. I did at first think that the problem could have been a thermostat that just so happened to go bad after the waterpump change, so I replaced it before I knew the monovalve getting a pulse whilke heat is aquired. Question, I think the push button assemply has gone bad, but it is a bit of a coincidence that this happened right after I changed the waterpump, I mean the customer said he never did have heat after he picked up his car. Any other clues, something stupid I'm missing here?.
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