I wondered if you've ever run into this problem I'm having with a tub.
I think it's haunted. I have an old Pacific Marquis(about 13yr) that
occasionally kicks on high pump speed and heater till the water
temperature overheats-all by itself. I'm on the 3rd thermostat to try
to fix, I replaced the soldered in pushbutton motor speed switch,
replaced power supply cap on board, replaced both mechanical timers,
cleaned/checked all relays-it still does it. It's such a simple circuit
I just can't understand why it happens. Without actually pushing the
mechanical switch, the pump should not turn on high speed-at the same
time the thermostat allows the water temp to rise to cutout. It's
almost like I pushed the pump button and ran the thermostat up myself,
but I'm not dreaming. Any thoughts? Norm