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circulation pump pushing enough water? did the technician test it when he was out?
I guess then the only other logical explanation, is weak pump, faulty switch, or faulty pcb ?If it's a flow switch rather than a pressure switch i'd assume that it has 2 states.ON or OFF.In which case, using a mutilmeter to figure out which way it works, i'd be tempted to short it out briefly and see if the error goes away.There are some knowledgeable chaps on here, some of which i believe are dealers and engineers, i'm surprised no one has piped up with an informed solution yet.
As far as shorting the switch I have done this on the PCB and it does not change anything.