Fujitsu Waterstage 77 fault code

What it means

Heat sink thermistor error (PFC)

Source: Fujitsu Waterstage Comfort D&T Manual DA_CF001EF, §Control System pp.03-2…03-4 (official-distributor mirrors) — numeric display codes with Fujitsu's own reset and runs-despite-error columns, plus the interface-card LED table

UK models this code applies to

Tap yours to open 77 on that machine.

Now the harder half: proving what caused it

77 names a symptom, not a root cause. In the app, the same code opens a guided investigation: what to measure first, the expected values for your exact model, and an honest verdict — including “nothing in this machine is broken” when that's what the readings say.

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