Thanks,
To check need to suspend thermo right in middle of a pryrex cooking pot filled with water, thermo must not touch lower pot, say middle heigtht. While water heats slowly, suspend a thermometer next to thermo, if opens at 60C? it's good. If at less than 60C? still good, OB will take bit more time to fully warm up. If more than 60C? Kaput...don't use it or risk having a powerhead overheat..
My thermo is in immaculate clean cond, don't know if with time, use and abuse goes bad, opens prematurely ?
Happy Boating