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Grundfoss 26-99FC variable speed failing
I have a Grundfoss 26-99FC that has run on Med speed for 11 years. This past spring we were travelling for 5 weeks and when I came home my indirect was calling for heat and the Grundfoss was not responding. I gave it the customary whack with a screwdriver and it has run fine until today. Assumed it just got hung up sitting at some point during our trip.
Today same indirect calling and warm,not hot second shower [mine of course] so I gave it a whack and it started again. Boiler has been under moderate use this winter.
When I switch speeds it always runs on low or high but perhaps 50% of the time when switching to medium it won't run. This makes me wonder if it is the switch failing and not the circulator? If it were a customer's unit I would replace the circulator to avoid additional service calls but since it is mine I am wondering if I can replace the switch?
Anyone else run into a multi-speed switch failure?
Can anyone describe how the switch works ? eg can I replace a resistor?
Thanks In advance Bill