Info, impact, causes, and troubleshooting a "Mainline Low Flow Variance Shutdown" message.

Common Causes

• Flow restriction on the mainline. 
• Issue with a zone valve connected to the mainline that isn’t opening fully.  
• Problems with pump performance or clogged pump intake could cause low flow.
• Flow variance limit may be set too low, causing the system to trigger a warning unnecessarily. 

What Happens Now? From the alert message:

• Expected vs Actual Flow (measured in Gallons per a Minute (GPM)) are given. The controller expected a combined 35 GPM from the three active valves that were running but only measured 26.1 GPM. This means Mainline 1 is not pressurized, so it has been shut. None of the zones will receive water until the variance message is cleared. Mainline 2 is not impacted.
• Flow Variance threshold (measured in %) is set to allow 20% variance, but the controller detected a 33.1%.There is a flow issue in one of Mainline 1's zones; zones 13,19 and 25.

Troubleshooting 

• Check for an obstructed mainline, such as a ball valve that isn’t fully open. 
• Inspect the zone valves, as one may be partially closed or obstructed. 
• Change the Flow Variance Thresholdif you believe it's too strict or wide:
  • Go into BaseManager → under Mainlines section → Flow Setup tab → Flow Variance Limit → In Flow Management, a 20% variance is set by default. 
    • However, Advanced Flow Variance may be a better option, as it allows you to set different variance percentage based on expected flow ranges. 
      • Ex: when the controller expects a combined flow of 25 GPM from zones, you might set a 30% variance. But when the expected combined flow is 300 GPM, you can tighten the variance to 5% for greater precision.