Rain and Freeze Sensors: Fort Worth Requirements and How They Work

A rain and freeze sensor is a small device that tells your controller when to skip watering. It is easy to overlook, but in Fort Worth it is often required. It also saves water and protects your system and sidewalks during freezing weather. This article explains how the sensors work, what the city requires and how to check that yours is doing its job.

What Fort Worth Requires

Fort Worth’s code requires properly working rain and freeze sensors on residential irrigation systems installed on or after June 1, 2007. Commercial and industrial systems have their own dates, and commercial sensors must be inspected and tested each year along with the backflow test.

The city’s irrigation code also says that all new automatically controlled irrigation systems must include operational technology that interrupts watering during freezing weather and during rain or high moisture. Repairs or alterations that require replacing an existing controller must include this technology too. Sensors must be installed according to the manufacturer’s published recommendations.

The city notes that new installations and retrofits to add these sensors require a permit obtained by a licensed irrigator or master plumber.

How Rain Sensors Work

Most rain sensors use a small stack of disks that swell when wet. When enough rain falls, the disks expand and push a switch that interrupts the controller’s signal to the valves. As the disks dry out, they shrink and the switch closes again, letting watering resume.

Many sensors have an adjustable setting that controls how much rain it takes to shut off the system, and a vent ring that controls how quickly it dries out.

Some sensors are wired to the controller; others are wireless with a receiver mounted near the controller.

How Freeze Sensors Work

A freeze sensor shuts off watering when the temperature drops near freezing. This keeps the system from spraying water onto lawns, sidewalks and streets that could turn to ice. Many products combine rain and freeze sensing in one unit.

Weather-Based Alternatives

Some smart controllers use weather data to skip watering during rain or freezing temperatures. Whether that satisfies the requirement depends on how the system is set up. If you have a smart controller, check with the installer. Our article on smart sprinkler controllers covers how they work.

Where Sensors Should Be Mounted

A sensor needs open exposure to rain and air. Good locations include a fence post, gutter edge or roof eave where rain falls freely. Poor locations include under trees, under roof overhangs, or near a dryer vent or air conditioning unit. A sensor mounted where it stays dry will never shut the system off; one placed in the path of sprinkler spray will keep it off too often.

How to Test a Rain Sensor

1. Make sure the controller’s sensor setting is set to active, not bypass.
2. Start a zone manually.
3. Press the test button on the sensor, if it has one, or pour water onto the sensor disks.
4. The zone should stop within a short time.
5. Let the sensor dry, or release the test button, and confirm watering resumes on the next cycle.

On wireless models, the receiver may show a signal or battery indicator. Replace the sensor battery if needed.

Common Sensor Problems

• Left in bypass. Many controllers have a switch that ignores the sensor. It is often left in bypass after testing or repairs.
• Worn-out disks. Over years, the disks lose their ability to swell. The sensor may stop shutting off the system.
• Cut or disconnected wires. Yard work, roofing and painting can damage the sensor wire.
• Dead battery on wireless sensors.
• Bad placement under cover or in spray.

Why the Sensor Matters

Fort Worth’s watering rules prohibit watering during rain. A working sensor is the simplest way to make sure your system does not run during a storm. It also helps during the rare hard freezes North Texas gets. Running a system when temperatures are below freezing can coat sidewalks and streets with ice and can put stress on exposed parts like the backflow preventer. Our article on protecting your backflow preventer from freezing covers that part of the system, and our guide to winterizing a sprinkler system covers the rest.

Sensors and the Controller Program

A sensor does not replace good programming. Your controller should still be set to your assigned days and to hours outside 10 a.m. to 6 p.m. Our controller programming guide explains how.

Replacing a Sensor

If your sensor is old or no longer responds, replacement is usually simple. Match it to your controller, mount it in an open spot and connect the wires to the controller’s sensor terminals. Some controllers need a jumper wire removed when a sensor is added. Because Fort Worth requires a permit for retrofitting sensors, it is best to have a licensed professional do it.

Seasonal Checks

Test the sensor at least twice a year: once in spring when you start watering regularly, and once in late fall before cold weather. Clean leaves and debris off the sensor while you are there. If the sensor is wireless, replace its battery on a schedule rather than waiting for it to fail. After roof work, gutter cleaning or painting, check that the sensor is still mounted in the open and its wire is intact, since these jobs often knock sensors loose.

When to Call a Technician

If your system does not have a sensor, the sensor does not respond, or you are replacing the controller, our sprinkler repair service can install or repair it.

Storms can knock sensors loose or damage their wires. Our guide to checking your system after spring storms includes the sensor in its list.