Yes, a dirty filter can keep your pool heater from firing

Yes, a dirty pool filter can absolutely reduce water flow enough that the heater refuses to ignite. It’s one of the most common reasons a pool heater won’t turn on.

Here’s what happens: most pool heaters have a flow switch or pressure switch that proves water is moving before it lets the gas valve open. When your filter gets clogged, it raises system pressure and drops flow. Once flow falls below the heater’s minimum, the switch stays open and the heater just sits there, no flame, no nothing.

You’ll usually see a flow error or low-water LED on the control board. But sometimes you won’t — the heater just silently refuses to cooperate.

Fix is simple: backwash or clean the filter. Also check the skimmer basket and pump basket while you’re at it. If flow was fine before and the heater stopped working around the same time you noticed the filter pressure gauge creeping up, start there.

Don’t assume the heater is broken. Clean the filter first, then see if the heater fires up.

Future you just saved a service call.