Irrigation Backflow Preventer Problems and Fixes in Minnesota

By Steve Grohn | Published 2026-07-08 | Updated 2026-11-12

An irrigation backflow assembly helps protect drinking water from reverse flow. Minnesota testing requirements depend on the assembly and installation date, and local rules may add requirements. A leaking or failed assembly needs qualified assessment.

Which testing rules apply?

The Minnesota Department of Labor and Industry fact sheet explains the state requirements:

For covered devices, the fact sheet calls for testing at installation and at least annually thereafter, with results submitted to the administrative authority and community public water supplier within 30 days of testing. Check with your city or water supplier for any additional local requirements. DLI also says a licensed plumber must install a device and a permit is required before installation.

Use DLI’s current certification information to check the person’s qualifications. A tester credential covers testing. A rebuilder must also hold a current plumbing license and the applicable ASSE certifications to install, maintain, repair, replace, or rebuild assemblies. The company’s plumbing license alone does not establish an individual’s backflow credentials.

What kind of protection does irrigation need?

A pressure vacuum breaker protects against backsiphonage under its approved conditions. An RPZ assembly uses check valves and a relief valve to protect against backflow under its approved conditions. The appropriate protection depends on the contamination hazard, potential backsiphonage or backpressure, elevation and local approval. Do not assume every irrigation system needs the same assembly. Ask the water supplier or plumbing authority about your installation. Minnesota Department of Health guidance discusses cross connections and protection.

Leaks, freeze damage and failed tests

A sustained leak or RPZ relief discharge can have several causes. Debris, worn components, pressure conditions and freeze damage all require investigation. Do not plug a relief opening. If water is escaping, shut off the irrigation supply only if you can safely identify its shutoff, and arrange a qualified assessment. A failed test guides further diagnosis; it does not automatically identify a single failed component.

A qualified person can assess whether cleaning, repair with approved parts, or replacement is appropriate, then test the assembly as required. Before the visit, record the manufacturer, model, serial number, last test date and any city notice.

Preparing for winter

Water trapped in an assembly can freeze and cause damage. Have a qualified person winterize and restart the system using the exact manufacturer’s instructions for that model and the local installation. Do not assume one compressed-air procedure, valve position or insulation method suits every PVB and RPZ. The Watts Series 800M4 instructions illustrate model-specific guidance.

Call 651-738-0580 to discuss your plumbing service needs and the qualifications required for your assembly.