Have you ever turned on your pool heater and heard a noise that sounds like rolling rocks—or maybe tennis shoes tumbling in a dryer? It can be unsettling, and it’s a common issue pool owners run into when cooler weather arrives and heaters get back into use.

The good news: this sound usually has a simple fix. That rattling or rumbling sound often means your heater isn’t getting enough water flow. Without sufficient water moving through the system, the heater can’t regulate properly—resulting in that loud, “something’s breaking” noise. Thankfully, a quick adjustment will solve it and protect your equipment.