Check and clean the backwater valve

What to do

Lift the access cap in the basement floor, look at the flap inside, and clear whatever has collected on it.

Why it matters

A basement fixture below street level is required to have one, and it is the only thing between a surcharged city sewer and your basement floor. Silted up it fails two ways: it will not close, so a surcharge comes in, or it will not open, so the house backs up on a dry day.

What to look for

• The flap swings freely and falls closed on its own — lift it with a gloved finger and let go
• Nothing caught on the hinge: grease, wipes, hair, gravel washed in from the sump
• The seal on the access cap is intact, and the cap goes back down tight
• No cracking or corrosion on the flap or its seat
• A second valve on the sump discharge line, if the house has a sump — it is a separate valve with the same failure

Where this comes from

National Plumbing Code 2020 2.4.6.4.(1), and 2.4.6.3.(7) for the sump discharge. The City of Calgary plumbing advisory of 4 October 2022 confirms the reading and adds that a normally-open valve may serve no more than one dwelling unit.