Raypak FLOW ERROR Error Code

What does Raypak FLOW ERROR mean?

Per the XTherm Error Display table, FLOW ERROR means the unit is not detecting enough flow to allow the ignition sequence to take place. The control requires proven water flow before it will fire the burner to protect the heat exchanger from overheating, so when adequate flow is not sensed it blocks ignition and displays the error. The related PIM water-pressure guidance directs checking system piping and the water pressure switch.

Symptoms

• FLOW ERROR shown as the active error on the display
• Ignition sequence will not start
• No-heat condition despite a call for heat
• Red fault LED on the PIM (water pressure / flow related)

Common causes

• Pump not running or running weakly
• Closed or throttled isolation valves
• Air-bound or low-pressure system
• Water pressure switch or wiring fault (J1 pins 6 and 7 jumper)

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Diagnostic steps

1. Verify the pump and flow

   Confirm the system pump is running and water is actually circulating through the heater.

2. Check system piping for leaks

   Per the PIM water-pressure guidance, check the system piping for leaks and confirm adequate system pressure.

3. Check the water pressure switch and wiring

   Inspect the water pressure switch (if equipped) and its connections, and check the wiring on the PIM at J1 pins 6 and 7 for a loose or missing jumper.

4. Open valves and purge air

   Verify isolation valves are open and purge air so the unit can detect proper flow.

5. Re-evaluate ignition

   Once flow is proven, confirm the unit proceeds through its ignition sequence without the flow error.

When to call a professional

A no-flow condition blocks ignition specifically to protect the heat exchanger, so it should not be bypassed. Diagnosing pump faults, hidden restrictions, and a water pressure switch on a hydronic system often requires gauges and system knowledge. If checking the pump, valves, and switch jumper does not restore proven flow, have a qualified Raypak service technician evaluate the hydronic system and flow-proving circuit.