GFI special use question

I have an artesian well which has a pump which runs on 240 volts. There is a breaker at the main box and another at the tank in the basement. Code does not require any kind of gfi for the circuit and the pump does not require neutral to operate. The house is in a cold region and I am worried about freezing pipes.
Here is what I have done. I have replaced the breaker at the tank with a GFI breaker. The hot wires of the breaker are connected to the pump as before, but I have connected the load neutral through a pipe mounted temperature sensor and then back to the line ground (the same ground the breaker is connected to). The sensor remains open as long as the temperature is above 35F. If the temperature falls, the sensor closes and trips the GFI like a charm (but I am not really sure why but it does) and thus shuts the pump off. It works like a charm.
(Some may ask, why waste that much money on a GFI 240 breaker. Answer, the pump is new and the old pump was 120V. Sensor and related wiring were already in place. The old set up was wired using the open at 35F lead instead of close lead.)
Any harm in doing this?
Thanks
Mike
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This is a first for me. Offhand I don't see anything wrong with it. One suggestion I could make is to use a GFI equipment circuit breaker which trips at 30ma instead of the standard 5ma type which is designed to protect people. You may have less nuisance tripping that way if it becomes a problem. The downside is that a 30ma breaker is around $300.00.
Shunt trip circuit breakers are also available that are typically connected to alarm systems and such. In the event of an emergency a relay closes and trips the breaker. SquareD makes them in the QO size.
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Ah, wish I knew that before I spend $120 on the breaker! And I thought I was pretty clever. ha. Thanks for the info.
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