Wells, Sump Pumps and Septic Sewage Systems - Freezing Sump Pump Pressure Switch?

I have a sump pump for my drain tile that is in the floor of a basement 7-8' below ground level. When it gets down to single digit temperatures, the alarm on my backup beeps indicating that the backup has been activated.

When I plug the primary pump directly into an outlet, it will run and eject water (which goes to a discharge pipe in the side of the house about a foot off the ground and then through a flexible pipe out into the side yard).

Reading other threads, it looks like freezing discharge pipes is common, but whether or not that is the case, I am not sure why the pressure switch won't work in single digit weather. The closet for the sump pump is in a heated basement, but the ground in the closet is very cold. I don't think it is possible for the ground to freeze 10' down in one night of single digits, but I am not sure what else could cause the sump pump switch not to kick on cold nights. If this is the case I am also worried that there is a bigger problem that might cause the well to crack or backup pump's float switch to stick.

Based on everything you describe, I think your best bet is to get the whole system serviced by the same people who installed it.

They will be able to determine what the problem is and suggest ways to fix it.

Beyond that, anything anyone here can say or recommend without actually looking at the pump itself, will be a guess.

A few questions that might help solve the mystery:
1. Does the main pump actually run in very cold weather, but not remove the water, or does it remain off?
2. Are the pumps submersible (under water in the sump)? (We know the water in the sump isn't solidly frozen, because the backup pump is able to move it.)
3. Does a film of ice form in the sump, which might "sabotage" the main pump's float valve but not that of the backup pump?
4. Does the water level in the sump actually get too high in cold weather, bringing on the backup pump, or is there perhaps some weird situation about the backup pump that causes it to needlessly run and beep in very cold conditions?

Yours is an excellent mystery, but there is sure to be a logical answer...I hope!

A few questions that might help solve the mystery:
1. Does the main pump actually run in very cold weather, but not remove the water, or does it remain off?
The main pump works and will move water if plugged in directly. However, the pressure switch in the pump well which interrupts the power supply is not activating in single digit weather (I am unsure why there is even water coming into the well when it is that cold...I assume the heat of the house melts some of the snow or ice in the ground).

2. Are the pumps submersible (under water in the sump)? (We know the water in the sump isn't solidly frozen, because the backup pump is able to move it.)
Yes, both pumps are submersible. The main was installed by a plumber and I installed the backup.
3. Does a film of ice form in the sump, which might "sabotage" the main pump's float valve but not that of the backup pump?
The main pump is a pressure switch, the back up is a float. The float switch fortunately does work and activates the backup.
4. Does the water level in the sump actually get too high in cold weather, bringing on the backup pump, or is there perhaps some weird situation about the backup pump that causes it to needlessly run and beep in very cold conditions?
I assume that the water level is coming in high enough to activate the backup, because a)it is beeping to indicate activation and b)when I have plugged the main pump directly into power to test it, it is kicking out water.
Yours is an excellent mystery, but there is sure to be a logical answer...I hope!


In follow up to my earlier post, I inspected the discharge outside and it is all clear of ice. I also had my wife activate the main pump while I was outside and it is ejecting water. My assumption is that the cold is somehow impacting the pressure switch. For $50 I would just try replacing the pressure switch, but I don't want to throw good money after bad and I am curious if this is even possible and if the sump well getting this cold is indicative of a much bigger problem.

CYFREE - Thanks for the sensible advice on having it inspected by a professional plumber and not just trusting my basement to free advice. That is definitely part of the plan, but my experience with plumbers to date (including and especially the ones who installed the primary system) has not been very favorable. My hope is to get some good ideas from objective sources who have maybe seen this set of variables, before I talk to someone who wants to sell me a $3K solution to a $50 problem.

Actually my advice was to talk to the people who installed the system for you because you wrote it is part of a drainage system that runs under the basement floor.

I don't know how old is your pump but usually those systems are either under some sort of warranty or service plan, so you should be able to have it serviced at little or no cost.

If the pump is not covered by either and you have to actually shop for a professional, here's a tip:

Have at least 3 different companies give you a free estimate. Chances are you will find one that will not try to push you a "5K fix for a $50 problem". :)

And don't be afraid of scary pushy sales tactics. If I am not mistaken every state now has a law version of the FTC "cooling off rule" (homeowner's best friend). Those laws give you a number of days (usually 3) to cancel a deal or a purchase you made, if the contract was signed out of the provider's place of business.

Check your state's attorney general website to see what is the time the law gives you where you live.

So...somehow the pressure-sensing switch is failing in very cold weather. If ice were forming in it, or in the pipe to it, then an incandescent light or heat lamp would (within an hour) cause it to work again and show you what needs to be insulated.

A quicker way to thaw the water tubing would be to pour a quart of water over it, but please don't do that near the electrical parts!

If there is no place for ice to form in it, then it may be getting stiff due to the cold. The light bulb should resolve that, and you can repeat every time you have extra-cold weather.

Note: Compact fluorescent lights are normally an excellent idea for lighting around the house, but in this case you need all that waste heat that incandescent bulbs put out.

The ambient air pressure in the pressure switch drops along with the temperature. It could be, if the pressure switch is very sensitive, that the increase in pressure with the rising water, added to the cold-lowered ambient pressure in the switch, in insufficient to activate the pump.

You might try, when the pump does not start on very cold days, pouring some hot water over the switch, or packing a rag soaked in hot water around it.

If this starts the pump, you might be able to wrap the switch with insulation or one of those electrical pipe warming tapes -- or even, on very cold night, just shine an infra-red light on the pump.

It sounds like your primary pumps switch has a piggyback plug on it as you can run the pump directly by plugging it in. I would just replace that pressure switch with either a regular float type or a verticle master if you don't have alot of room in the pit. Not a fan of pressure switchs.