Backwater valve closed and toilets won't flush in Calgary, why?

A closed backwater valve and toilets that won't flush almost always mean the same thing: sewage is backing up from the city sewer main toward your house, and the valve has done exactly what it was installed to do, sealing shut to keep that sewage out. The toilets won't flush because there is nowhere for the water to go.

What is actually happening

Your backwater valve sits on the sewer line where it leaves your house. When the main sewer is overwhelmed, typically during a heavy rainstorm or a spring melt event, sewage can reverse direction and flow back toward homes on the street. The valve's flap closes automatically when flow reverses, blocking that sewage from entering your basement. While it is closed, your home's drain system is essentially sealed: toilets, floor drains and basement fixtures cannot drain, so flushing pushes water with nowhere to go.

The right response right now is to stop using water in the house. Do not flush toilets, run the dishwasher or do laundry. If sewage has already entered the basement, keep people away from it and arrange proper cleanup; sewage exposure is a health hazard and is not a straightforward DIY job.

Once the city sewer pressure drops, the valve flap should open on its own and normal drainage will resume. You can check the valve's access cover in your basement floor to see whether the flap has returned to the open position before you start using fixtures again.

Check with the City of Calgary first. The City can send a crew to run a steel snake to the sewer main at no charge to determine whether the blockage is on the City's side or your private sewer line. If it is on the City's side, they handle it. If the blockage turns out to be on your private line, they will tell you to call a plumber. That free assessment is worth doing before you pay anyone.

If the valve itself is damaged, stuck closed after the event, or has never been serviced, a plumber will inspect and clean or replace it. Installing or replacing a backwater valve in Calgary requires a plumbing permit from the City of Calgary. The price depends on how deep the valve sits and how much concrete has to be cut to reach it, so get an itemized quote rather than a single number.

A certified plumber should do any work on the valve or the sewer line. Before hiring, ask to see their trade certificate, a WCB-Alberta clearance letter confirming their account is in good standing, and, if you are paying a deposit before the work is finished, confirm they hold an Alberta prepaid contracting licence through Service Alberta.

When you compare quotes, ask each plumber to break out the permit fee, concrete cutting and patching, and disposal separately, because that is where the gap between a low headline number and the final invoice tends to hide.