I know that it is always a concern that a float switch might become stuck and continue to allow water to be pumped into a tank resulting in a tragedy.

I'm sure I'm not the first person to do this but I've never seen it mentioned anywhere. If you were to plug the ATO unit into a timer and have the timer set to come on two or three times a day for only a few minutes each time, it seems this would avoid any catastrophic failures. The timer could be fine tuned to where it would allow enough water (and maybe just a little bit extra) to be pumped into the tank to replace any evaporation, and then the timer would shut off. If the float switch became stuck, only as much water would flow into the tank as the timer would allow. By setting the timer where it would come on during a period when you usually observe the tank, it would be possible to notice a problem and have time to correct it before a catastrophy happens. Or if you noticed the water level to be above the normal shutoff level of the float switch, that would be a clue to take corrective action.

Before I had a real auto topoff system, I was using a timer to turn a pump on for a few minutes each day. I had the timer set to not quite fill the tank back to the desired level which would allow me to only have to manually add topoff water a couple of times a week. The method I described above is taking the best of both worlds. Instead of the redundancy of multiple float switches (which could still fail) this seems foolproof to me.

Does anyone here see any problems with doing this?

Cool.

I feel validated.

I have 2 float switch on mine, but my water reservoir only limited to 5 gallon, so just in case both switches got stuck, the max water that can be pump into the sump is only 5 gallon.  I have about 10 gallon extra space for water in the sump at operating level.

stan

But wount your top of pump burn  up then?

I guss I dont under stand what you are saying.

He stated he onley has a 5 gal and it will holed 10 more gal in his fuge.

Well if the floats get stuck its still going to drop the salinity with 5gal and burn up the pump.

5 gallons in a 210 gallon tank is not going to be a very large drop in salinity. In addition in the OP, Tom mentions using a timer. This timer is only on for a few minutes. So even if the float switch failed and the 5g was dumped into the tank. The timer would eventually turn the pump off. Now if the float and timer failed it would still only dump 5 gallons of water in the tank. Nominal change. In this case though the pump would continue to run and could burn up if not caught.

I think the idea here is that ONLY 5 gallons would ever enter his system, max. Which is ideal. I would not want the system to continually pump water into the tank. I personally am not concerned about a $12 pump.

Right. But the post I had reply to was about the person haveing 2 float valves so they did not use a timer. And as a back up they onley keept 5gal on hand. So frome my understanding they wher saying they did not need to use the timer because of the 2 floats and haveing onley 5gal back up.

I was just geting at he be better off with one float and the time.