Winterizing via Controller Fails? Flow Sensor May Block Air Blowout

If your Nelson controller flashes "no water supply" when trying to blow out zones with a compressor, you likely have a flow sensor that detects no flow (air doesn't trigger it) and inhibits valve operation.

Key Questions

• Is this a commercial system? (Flow sensors common there)
• Compressor size? (Need 50+ CFM for proper blowout)
• Did you blow out before the backflow preventer?

Critical

Backflow preventer must be blown out — it's the most expensive component and first to freeze-break.

Workaround

Manually open bleed screws (as you did) or bypass flow sensor temporarily. Consult manual for sensor override.