How to Start Up an Irrigation System After Winter in Colorado

Introduction

Spring irrigation startup is one of the most skipped maintenance steps on the Front Range — and one of the most consequential. Homeowners turn the system on, walk a zone or two to make sure the heads are popping up, and call it done. What they miss is the damage that accumulated over winter: cracked heads that spray sideways at low volume, valve diaphragms that stuck in the cold, a zone that pressurizes slowly because there's a break somewhere in the lateral, or a backflow preventer that's been leaking since the first hard freeze in November.

A methodical startup takes an hour. Finding the damage it would have revealed — weeks later, after you've been running the system at full pressure — takes considerably longer and costs more to fix.

Why This Happens in the Front Range

Colorado's freeze-thaw cycle is the root cause of nearly all irrigation startup problems. Even in a year where you had the system blown out properly in October, winter creates conditions that degrade irrigation components in ways that only become visible under pressure.

Backflow preventers are above-grade by code, which means they experience the full range of ambient temperatures over winter — including the extended single-digit periods that hit the Front Range in January and February. Valve solenoids and diaphragms inside valve boxes are insulated by the soil around them but can still freeze in severe cold. PVC lateral lines in low spots or flat runs may retain water that a blowout didn't fully clear, and that water expands and cracks the pipe from the inside.

The soil itself matters too. Front Range clay holds cold longer than sandy soils. Shaded areas of the yard, particularly on north-facing slopes or beneath dense evergreens, may still have frozen ground in April while the rest of the yard looks ready to go. Pressurizing a system while a section of lateral is still in frozen soil doesn't cause immediate damage, but running it repeatedly before the ground fully thaws stresses fittings that are already marginal.

Common Signs Homeowners Notice

A zone that runs but shows no pressure at the heads. Either the valve isn't fully opening or there's a break in the lateral. Both need diagnosis before the zone is run at normal pressure.

Heads that don't retract after the zone turns off. Debris in the head, a cracked wiper seal, or a housing that distorted over winter. A head that stays up is a trip hazard and will be mowed over.

Wet areas appearing within an hour of first startup. A break in the lateral is leaking into the soil. The wet area will often appear a few feet away from the actual break location due to how water moves laterally through clay.

A zone that runs without turning the controller on. A stuck valve — usually a diaphragm that didn't reseat after the last fall blowout or froze in the open position. The zone runs continuously regardless of controller input.

The backflow preventer dripping or spraying from the test ports. This is the most common single-point failure after a hard winter. It can range from a minor drip to a continuous stream depending on the extent of the freeze damage.

Practical Steps Homeowners Can Take

Start with the water supply, not the controller. Open the main isolation valve slowly — over the course of 30 to 60 seconds. Sudden full-pressure startup sends a pressure surge through the system that can dislodge weakened fittings and crack heads that are already compromised. Slow pressurization lets you hear problems before they become larger problems.

Inspect the backflow preventer before running any zones. Once the main is open, check the backflow preventer visually for cracks, drips at the test cocks, or spray from the housing. If there's active leakage, close the main and address the preventer before continuing. Running zones with a leaking backflow preventer wastes water and can create a cross-connection issue with your supply line.

Test each zone manually from the controller, one at a time. Don't run a full watering cycle on the first startup. Walk each zone while it's running. Confirm that heads pop up, spray in the correct pattern, and retract when the zone ends. Note any heads that are obviously cracked, spraying sideways, or not functioning.

Check valve boxes for standing water or visible damage. Open each valve box and look at the solenoid connections and wiring. Rodent damage to wiring is common over winter in foothills communities. Waterlogged valve boxes that didn't drain over winter can indicate a drainage problem at the box itself.

Run each zone for a full cycle and walk it again. The first walkthrough catches obvious problems. A second pass after a full zone run reveals the slower leaks — a head that sprays normally for 30 seconds and then starts leaking at the base, or a zone that loses pressure gradually over a 10-minute run.

Check and adjust head arc and radius settings. Heads shift over winter from frost heave, foot traffic on saturated soil, and settling. Rotors that were aimed correctly in October may be watering the sidewalk or the neighbor's fence by April.

Document anything that needs repair before running the full schedule. Running a full automated watering schedule before fixing identified problems turns a $50 repair into a $200 water bill plus a $200 repair.

When to Call a Professional

Backflow preventer replacement requires a licensed plumber in most Front Range municipalities — it's not a DIY repair even if you're comfortable with basic irrigation work. If your preventer failed over winter, call before startup rather than after.

If you're finding a lateral break but can't locate it by the wet area above ground, an irrigation contractor with pressure testing equipment can isolate the break without excavating the entire zone. In clay soil, exploratory digging without knowing where the break is can take hours. Professional diagnosis takes 20 minutes.

If multiple zones have issues or the controller itself isn't responding correctly to manual commands, the problem may be in the controller wiring or the controller unit itself. Irrigation systems that were installed more than 15 years ago may have controllers that are no longer supported, and replacement is often more cost-effective than repair.

Conclusion

Irrigation startup done right takes about an hour and costs nothing beyond your time. Done wrong — or skipped entirely — it costs weeks of undetected water loss, dead zones you don't notice until July, and repair bills that a slow pressurization and one careful walkthrough would have prevented entirely. The Front Range's freeze-thaw cycle will find every weak point in your system. A methodical startup finds them first.