Aside from preventing debris from floating back out into the pool, weir doors actually have a bigger job than most people realize. One of those functions is to properly regulate the flow of water into your skimmer boxes. This is apparent when there are a lot of people in the pool and the water level goes up and down (think of the waves caused by people splashing around).
The weir door keeps the water inside the skimmer box level and prevents fluctuation of that water level. Waves in your pool can cause your skimmer box to take in big gulps of air that may cause your pump to lose prime (i.e. air inside the pipes). Read more about how to prime your pump here.
Too much water on the other hand (again, think of the waves) can overfill your skimmer box and push the trapped debris in your skimmer basket to float back out into the pool.
Another important thing to think about when talking about weir doors is that if a weir door is stuck, it can prevent water from properly entering your skimmer boxes, which in turn causes a drop in pressure and your pump to pulse or surge.
So the next time you see a problem with your weir door, replace or repair it immediately to help avoid unnecessary pool maintenance in the future.Don’t forget to check out our collection of pool & spa maintenance supplies for other parts and fittings to keep your pool in tip-top condition.