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No display on AM10

A Buderus GB142-24 was making DHW but no space heat to the rads.  The AM10 had worked for several years but now the display was blank.  After powering down, disconnecting the AM10, moving the potential-free thermostat  wires from the AM10 "On/Off" terminal to the WA terminal, and powering up, the system went to work.  Instead of modulating from the outdoor reset, they rad water temp is now controlled by the space heating temperature knob, set to 165 degrees.  With the AM10 display going blank, would you replace the AM10 or do other testing?