Raypak DELTA T

What does Raypak DELTA T mean?

Per the Error Display table, DELTA T means the temperature difference between the inlet and outlet exceeded the set point, and the manual instructs to check water flow. The control compares inlet and outlet sensors; an excessive rise indicates water is not moving fast enough through the heat exchanger to carry away the heat being added. The PIM logs this as a hi-temperature delta fault.

Symptoms

• DELTA T shown as the active error on the display
• Calculated rise across the heat exchanger above the set point
• Red fault LED (13 flashes indicates hi-temperature delta fault on the PIM)
• Often paired with weak or no circulation

Common causes

• Insufficient water flow across the heat exchanger
• Pump not operating correctly
• Air-bound or partially blocked piping
• Closed or throttled isolation valves

Diagnostic steps

1. 01

   Check water flow

   Per the Error Display instruction, confirm there is adequate water flow through the heater.

2. 02

   Check pump operation

   Per the PIM delta-fault guidance, verify the pump is running and confirm proper water flow across the heat exchanger.

3. 03

   Purge air and open valves

   Purge air from the system and verify isolation valves are open so water circulates freely.

4. 04

   Reset the control

   After restoring flow, press and release the RESET button to clear the fault.

5. 05

   Observe operation

   Monitor several cycles to confirm the temperature rise stays within the set point.

When to call a professional

A high delta-T usually points to a flow problem that can stress the heat exchanger over time. Diagnosing pump performance, flow rates, and hidden restrictions often requires gauges and system knowledge. If the cause is not an obvious closed valve or air pocket, or the fault returns after purging, have a qualified Raypak service technician evaluate the pump and hydronic flow.