Pentair MasterTemp ERR PS — Pressure Switch Failure Guide

Error Code: ERR PS

What it means

The ERR PS code tells you the pressure switch circuit has opened or failed to close. Your Pentair MasterTemp or MiniMax heater thinks there is no water flowing. The pressure switch is a safety device that confirms adequate water flow before the heater fires. When it stays open, the control board refuses to start.

Common Causes

• Flow restriction upstream. A dirty filter, closed valve, or partially blocked skimmer basket starves the heater of water.
• Suction-side air leak. A loose pump lid gasket or leaking union pulls air into the system. Air reduces the pressure differential needed to close the switch.
• Pump not priming properly. If the pump loses prime, water movement stops and the switch stays open.
• Water level dropped below skimmer. The pump pulls air once the water level falls below the skimmer opening.
• Faulty pressure switch. The switch itself can fail mechanically or electrically. Internal corrosion, stuck diaphragm, or burned contacts prevent closure.
• Thermal regulator bypass valve stuck open. This spring-loaded valve inside the heat exchanger diverts water around the burner. If it sticks open, the pressure differential across the switch drops below the trip point.
• Water chemistry issues. Low pH or high calcium scale fouls the pressure switch port over time. Scale buildup prevents the diaphragm from moving freely.

Step-by-Step Fix

1. Check flow at the pump. Look at the pump strainer lid. Is it full of water? A half-empty lid means you have a suction leak. Inspect the pump lid O-ring for cracks and the drain plug for leaks. Turn off power before handling electrical parts.

2. Inspect the filter pressure gauge. If the gauge reads 10 PSI or more above your clean filter pressure, backwash or clean the filter. A clogged filter is the most common cause of low flow.

3. Verify all valves are open. Check the valve position between the filter outlet and the heater inlet. A partially closed valve creates enough restriction to drop pressure below the switch threshold.

4. Confirm minimum flow rate. MasterTemp needs 40 GPM. MiniMax needs 30 GPM. Calculate your flow rate by reading the pressure drop across the heater or timing how long it takes to fill a 5-gallon bucket at a return line.

5. Test the pressure switch with a multimeter. Disconnect the two wires from the pressure switch. Set your multimeter to continuity or resistance mode. With the pump running, you should measure continuity (near zero ohms). With the pump off, the switch should be open (infinite resistance). If the readings are reversed or stuck in one position, replace the switch.

6. Check the touchpad diagnostic LEDs. On MasterTemp heaters, press the POOL/SPA button and then press ON. Watch the LED sequence on the control board. Three flashes followed by a pause means pressure switch fault. Five flashes means high limit switch. The LED pattern helps you confirm the error source.

7. Test the thermal regulator. Remove the regulator bypass valve from the top of the heat exchanger. Warm it in your hand. A functioning valve begins to open around 105 degrees F. If it rattles freely when cold or feels stuck, replace it. A stuck-open valve lets too much water bypass the switch port.

8. Inspect the switch port for scale. Remove the pressure switch from its port. Look inside with a flashlight. White crusty buildup means calcium scale. Clean the port with a small brush and white vinegar. Rinse thoroughly before reinstalling.

9. Reset the heater. After fixing the cause, press the POOL/SPA button and then press ON. The heater runs through a self-check. If the error clears, you fixed it. If ERR PS returns immediately, the switch or control board needs replacement.

Parts That May Need Replacement

Technician Tips

The pressure switch on MasterTemp heaters is normally open. The switch closes when it senses sufficient pressure. This means the switch is never closed in a static system. You must verify continuity with the pump running.

Suction-side air leaks are the most overlooked cause of ERR PS. A single loose thread on a pump lid can introduce enough air to drop the pressure differential. Listen for a hissing sound near the pump suction. Feel for vibration or rattling in the pump lid.

Scale fouls the switch port faster in areas with hard water. If you replace pressure switches every season, test your water chemistry. Keep pH between 7.4 and 7.6. Keep total alkalinity between 80 and 120 ppm.

Never run the heater with the pressure switch bypassed or jumpered. The switch is a safety device. Bypassing it means the heater can fire with no water flow, which destroys the heat exchanger in seconds and creates a scalding hazard.

Need Replacement Parts?

Shop Pentair MasterTemp Pressure Switch Parts on Amazon

When to Call a Professional

Call a licensed pool technician if you have confirmed the pressure switch and thermal regulator are good but the error persists. A control board failure requires a multimeter and schematic reading. Most homeowners should not replace control boards without experience.

Call a professional if the heat exchanger shows signs of internal scaling or blockage. Flushing a scaled heat exchanger requires acid washing. Improper acid washing can damage the copper tubing and void the warranty.

Call a professional if gas components must be removed to access the pressure switch. Relighting the pilot and verifying gas pressure require specialized training.

See Also

• Pentair Pool Heater ERR IGN, ERR AGS, and ERR HLS Guide
• Pentair Pool Heater Error Code Complete List
• Pool Heater Low Flow Diagnosis Guide
• Pentair MasterTemp Control Board Replacement Guide

Related Articles

• Pentair Pool Heater ERR IGN, ERR AGS, and ERR HLS Guide
• Pentair Pool Heater Error Code Complete List
• Pool Heater Low Flow Diagnosis Guide
• Pentair MasterTemp Control Board Replacement Guide