Home Improvement → Re: Sump Pump - Discharge riser freezing

You aren't understanding where it's freezing. The check valves at the pump ensure that any water pumped out doesn't drain back into the sump once the valve shuts off. That results in water standing in the pipe up to the top of the most vertical run of the drain pipe. After the pump shuts off, water is draining so that it's flush with the bottom of the horizontal run that heads through the wall. It's freezing right at this spot because either outside air is cooling through the pipe, or more likely the large vent directly beside where the pipe goes through the wall.

The water is not remaining at that level because of an air lock. An air admittance valve like you describe would not do anything. The solution to the problem is that either the air at that spot needs to be kept above freezing, or the water level in the drain needs to be lowered to a spot where the air temperature is above freezing. The latter can not (easily) be done with the check valves in place unless they are somehow bypassed, defeating some of their purpose of not having to re-pump water that's drained back into the sump.

Thanks all for the input.

CDRU is bang on with where and how it is freezing... prior to my previous sump pump failure, I only had a single pump without a check valve. The stand pipe would drain back after each pump out and, effectively, double the number of pumps required to maintain the pit. That said, it also eliminated the freezing issue but increased the possiblity of an air lock on the pump.

I bought some Big-O end caps last night and stuffed the vents full of pink insulation before capping with the end caps. I do not want a permanent solution plugging the hole as they ventilate humidity in the summer. For those who aren't familiar with this type of setup, this 'room' is the area under the front concrete porch. It is separated for the basement proper by a steel insulated door and the room has no source of heating or cooling. Basically, it normally stays about 4C in the winter and about 12C in the summer. This has been an exceptionally cold winter but I want a solution that will be permanent.

When at the HoPo last night, I looked at the heater tape and spoke to one of the 'plumbers' at the HoPo (remember when Home Depot used to have knowledgable workers... it seems sometimes now it is whoever can fill out an application although some are still very good). The cables indicate they should not be used on drain pipe (supply only). I expect this is due to a fire hazard if the drain is empty and the heater is running? Comments? Someone with more knowledge than the 'plumber' at the HoPo?

Hoping a permanent solution is discovered before this cold snap stops and I have no way of testing whether anything is working

From their webpage:
Warning: This cable has been designed for the sole purpose of preventing metal and rigid plastic water filled lines from freezing. DO NOT use this product on fuel lines, drain lines, hoses or buried pipes.

Guess that's right.

Another one to scratch from the list.

That leaves three options as far as I can see (if the insulation doesn't work).

1. Try your light bulb method.
2. Move the line away from the wall as stated above.
3. rig something to drain the top foot of water or so from the pipe.

Some are designed only for metal supply lines. Others can work on drain. Freeze Free specifically mentions plastic drain pipes. It's only 3 watts per foot of cord with a 5' kit available in retail packaging.

Your application would be a little different then a typical drain application as your drain pipe usually would contain water. If indeed it runs a few times a day in winter, I doubt it will evaporate enough between pumps that it would run dry. Installing the heat tape a little below the 90 going outside would also provide additional time before it evaporated off, presuming convection currents in the water were enough to keep the top surface from freezing.

Another option is just to replace the plastic line with a metal one.

Ahh ok, so basically its in your cold room, thats a different story, yup for now i think the only recourse is to block the fresh air holes for the winter and maybe put a light bulb in there for the duration of the cold spell as HM says

Long term solution for me would be to move it away from the wall this summer.