What Happens if a Sprinkler Fuse Blows?

Automated sprinkler systems ensure the landscape is watered when needed. However, these systems are complex and have numerous components that all need to function properly for the system to work as intended. A blown fuse inside the sprinkler controller is one indicator that something has gone awry. It is simple enough to replace the fuse, but the underlying cause must be determined to keep it from blowing again.

Effect of a Blown Fuse

  1. A sprinkler system does not function at all if the fuse blows. Most controllers will have a message in the display indicating that the fuse has blown. The control box may still have electrical power, but the valves will not open or close. This means the sprinklers will not run and there is a risk that the soil will dry out and plants will suffer. If it blows while part of the landscape is being watered, that valve will remain open and the sprinklers will continue to run until shut off manually.

Confirmation of the Problem

  1. If the sprinklers are not coming on as they should, any number of things could have gone wrong. The only way to verify that a blown fuse is the problem is to inspect it visually. In most controllers, the fuse is located behind the control panel where the wires to the valves are connected. There should be a tab on the side of the box that will release the face of the control panel, allowing it to hinge open and give access to the fuse. The fuses are virtually identical to those used in cars -- it is a cylindrical glass tube about 3/16 inch in diameter with two metal caps on either end. A tiny metal filament inside the glass tube ruptures when the fuse blows, which should be evident with a visual inspection.

Fuse Replacement

  1. Unplug the sprinkler controller from its power source. Pull the blown fuse out of the clips that hold it by hand -- do not attempt to use pliers, since the glass could break. Some controllers come with a spare fuse taped to the inside of the panel door that can be used as a replacement. Otherwise, check the amperage and voltage ratings printed on the metal caps and replace with an identical fuse. These can found at irrigation supply stores or ordered directly from the manufacturer of the controller.

Underlying Causes

  1. A faulty solenoid is the most common cause for a blown fuse. If the fuse blows again when a particular valve is turned on by the controller, try replacing the solenoid on that valve. It is also possible that a short has occurred in the wiring between the valves and the controller. Check to see if the line has been cut or damaged in any way. If neither of these is the problem and the fuse continues to blow, the controller itself may be faulty and needs to be replaced.