Where To Start?

Check that your pump/filter are in good working order.
Identify the type of pool filter you have – sand, cartridge, diatomaceous earth.
Check that the pump and weir baskets are intact.
Know the size of your pool.
Know the type of pool lining.
Understand how the pump timer works – refer to the operating manual.
Understand the different multiport valve settings.
Check that the pool water is topped up.
Have a pool water test kit available.