Hi All
Good to see input on safety related issues All points are good value
In so far as the pump not being able to run so you can fill the reactor again there is a simple way around that
A two way switch marked Safe Manual will by pass the open circuit
It can be spring loaded so it can only function while you are holding it down Since you only have to get a very small qty of material out or in before the reed switch makes the circuit it would not take that much time
I am sure there is a heap of other ways as well
However this is a fairly low cost set up
A s/h contactor is about $10 if you where to get two it will make it even better as well as safer,
One contactor wired self latching to supply power to all of the system the other for the element
You wire one of the contactors as self latching with a push button labeled Start
It will come on when you press it suppling power to the whole system
If there is a power outage it will stay off until you press the start button again
The element contactor can then control temperature via the safety circuit mentioned before
A reed switch is about a $1.50 new
I am sure there are enough around from alarm systems that no one wants at the local demolition yard
The two way switch, since it only has to carry the current for the contactor which is in the milliamps may be about $5.00 from the local electronics store and about $10.00 of cable
So for about $30-$40 one can have a fair amount of "insurance"

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Cheers
Chris
Never give up :)