Raypak UNDER FLOW Error Code

What does Raypak UNDER FLOW mean?

Per the XTherm Error Display table, UNDER FLOW means the flow reading has dropped under the minimum requirements to keep the current operation point. The heater had been running, but circulation fell below what is needed to safely sustain the present firing rate, so the control flags the condition to protect the heat exchanger from an excessive temperature rise. It points to a developing flow or pump problem during operation.

Symptoms

• UNDER FLOW shown as the active error on the display
• Heater reduces or stops firing during operation
• Flow below the minimum for the current operating point
• May precede a DELTA T or LIMIT TRIP condition

Common causes

• Pump weakening or partially failing under load
• Partially closed or fouling valve
• Air accumulating in the system
• Strainer or piping restriction developing during operation

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Diagnostic steps

1. Check the pump and circulation

   Verify the system pump is running at full capacity and water is circulating at the required rate during operation.

2. Inspect valves and strainers

   Check that isolation valves are fully open and inspect any strainers for fouling that would reduce flow.

3. Purge air from the system

   Purge air that may be accumulating and reducing the effective flow through the heater.

4. Confirm system pressure

   Per the manual's water-pressure guidance, check system piping for leaks and confirm adequate pressure to maintain flow.

5. Observe under load

   Run the heater at its operating point and confirm flow stays above the minimum without the under-flow error returning.

When to call a professional

Flow that drops during operation indicates a developing hydronic problem that can overheat the heat exchanger if left unresolved. Diagnosing a weakening pump, intermittent restriction, or air problem under load usually requires flow measurement and system experience. If clearing air and opening valves does not maintain adequate flow, have a qualified Raypak service technician evaluate the pump and piping.