Heater Assemblies Flow Thru- all electrical heaters basically work the same way. Heat is created by a current that is passed through the element. If this current flow is stopped, there will be no heat. If the hot tub heater turns on with no water flow, you will burn up and damage the heater. Most hot tubs are equipped with pressure and high limit switches to avoid this problem though. The most common kind of heater for hot tub is a flow thru. It's mounted horizontally to the spa controls. It can be placed anywhere around the control box area and will have a cord that goes from your spa control to the heater. It's mounted near the control box because when there's a problem with the controller, there's usually a problem with the heater. The two usually go hand in hand. With flow through heaters, it's possible to change just a part without replacing the entire heater itself. Sometimes the entire heater will have to be replaced because of corrosion or bad plumbing. But mostly, just the heater element can be replaced quite easily. Some heaters have a sensor mounted system and some pressure switch (usually older models). When you order a spa heater, make sure you order the correct voltage (120v or 220v) and the correct kilowatt rating as well. Electrical repairs can be dangerous, especially around water. Please make sure you have someone qualified to do your electrical work and ALWAYS unplug and disconnect your hot tub before making any repairs!
