Winter is upon us,
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>
> (unfortunately there's no snow so the frost is going deep).
>
> We have an outdoor, above ground insulated cistern that we heat with a
> 120Vac sump pump that's works well.
>
> The problem is it's manually controlled, which is inconvenient when we
> leave for a week or two...
>
> So we need a thermocouple (thermistor) we put into the cistern and cycle
> it to keep the water temperature at 40F.
>
> Is there something on the market that can do that, I've looked and
> haven't found anything yet.
> If not, I'll design and market one.
> Ken
Have you called your local well pump supply outlets? That sounds like just the sort of thing they'd have.