Staff Answer
Sep 28, 2026 - 07:30 AM
That small "o" usually means the high-temperature limit circuit is open. Since the cooling unit was replaced last year, check the limit switch and its wires on the boiler first. They're easy to leave loose or damaged during a cooling unit swap. The popping sound could have been a fuse, so check those too. If the limit switch has continuity and it still shows "o," the switch or board is next. If the limit keeps tripping, the cooling unit may be overheating.
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