Pentair MasterTemp Error Codes: Complete Troubleshooting Guide

Some MasterTemp problems are caused by simple circulation issues, such as a dirty filter or closed valve. Other faults involve gas, combustion, wiring, or internal heater components and should be diagnosed by a qualified pool-heater technician.

This guide explains the most common Pentair MasterTemp error codes, what they generally mean, and what to check before scheduling service.

Pentair MasterTemp Error Codes at a Glance

Pentair’s MasterTemp platform uses multiple safety switches and sensors to stop heater operation when unsafe water-flow, airflow, temperature or ignition conditions are detected. The exact display wording can vary by heater age and control-board version.

ERR PS: Water-Pressure Switch Open

The ERR PS code means the heater is not detecting sufficient water pressure or circulation.

The pressure switch must close before the heater is allowed to ignite. This protects the heat exchanger from firing without adequate water flow.

Common causes

• Pool pump is off or running too slowly
• Dirty filter
• Full pump basket or skimmer basket
• Closed or partially closed valve
• Low pool-water level
• Air trapped in the plumbing
• Clogged impeller
• Incorrectly adjusted or failed pressure switch
• Heater installed above or below pool level without proper switch adjustment

What to check

1. Confirm the circulation pump is running.
2. Increase the pump speed temporarily.
3. Clean the pump and skimmer baskets.
4. Check the filter pressure and clean or backwash the filter if needed.
5. Verify all plumbing valves are correctly positioned.
6. Look for air entering the pump basket.

Do not bypass the pressure switch. If circulation appears normal and the code remains, have the pressure switch and wiring tested by a qualified technician.

ERR HLS: High-Limit Switch Open

The ERR HLS code means the heater’s high-limit safety circuit has detected excessive internal water temperature.

The HLS protects the heater from damage when water inside the heat exchanger becomes too hot. Pentair identifies the high-limit switch as part of the MasterTemp electrical safety system.

Common causes

• Insufficient water flow
• Dirty filter
• Low pump speed
• Closed valve
• Scaled heat exchanger
• Sticking internal bypass valve
• Thermal-regulator problem
• Failed high-limit switch

What to check

Start with the same circulation checks used for ERR PS. A heater may have enough flow to close the pressure switch but still have insufficient flow to carry heat away properly.

Repeated HLS faults should not be ignored. Continued overheating can damage the heat exchanger, manifold and other internal components.

ERR AFS: Airflow Switch Open

The ERR AFS code indicates that the combustion-air safety switch did not detect the expected airflow.

The MasterTemp is an induced-draft gas heater. Its blower must establish proper airflow before ignition can safely occur. Pentair describes the MasterTemp as an induced-draft heater using direct ignition rather than a standing pilot.

Common causes

• Blower is not running
• Blower is running too slowly
• Blocked air intake
• Restricted exhaust vent
• Debris inside the heater
• Damaged airflow tubing
• Faulty airflow switch
• Loose wiring connection
• Incorrect vent installation

What to check

• Listen for the blower during the ignition sequence.
• Inspect accessible intake and exhaust openings for debris.
• Make sure nothing is covering the heater or blocking ventilation.
• Check for visible damage from rodents, insects or moisture.

Do not operate a gas heater with a blocked vent or suspected combustion-air problem. Exhaust and combustion testing should be performed by a qualified technician.

ERR IGN: Ignition Failure

The ERR IGN code means the heater attempted to light but did not successfully establish or prove a flame.

Common causes

• Gas shutoff valve is closed
• Propane tank is empty or low
• Gas pressure is incorrect
• Gas line is undersized
• Air is trapped in a recently serviced gas line
• Hot-surface igniter is damaged
• Ignition-control module problem
• Gas valve failure
• Burner or orifice obstruction
• Wiring or grounding problem

Safe homeowner checks

• Confirm the external gas valve is open.
• Confirm other gas appliances are operating normally.
• For propane systems, verify the tank has fuel.
• Turn the heater off and allow it to complete a reset before trying again.

Do not repeatedly restart a heater that smells like gas. Turn the heater off, close the manual gas valve and contact the gas supplier or a qualified heater technician. Pentair warns that improper heater installation or service can cause fire, explosion, injury or death.

ERR AGS: Automatic Gas-Shutoff Switch Open

The ERR AGS code means the automatic gas-shutoff safety switch has opened because the heater experienced an excessive internal temperature condition.

This fault generally deserves more immediate attention than a basic flow warning.

Common causes

• Severely restricted water flow
• Scaled heat exchanger
• Failed or sticking internal bypass
• Thermal-regulator failure
• Improperly positioned valves
• Failed AGS switch
• Wiring problem

The AGS switch is a genuine part of the MasterTemp heater’s electrical safety system.

Avoid repeatedly resetting an AGS code without finding the cause. A technician should inspect the heater’s water system, bypass, thermal regulator, heat exchanger and safety circuit.

ERR SFS: Stack-Flue Sensor Fault

The stack-flue sensor monitors exhaust temperature. An ERR SFS condition can indicate excessive stack temperature, an open safety circuit or a sensor-related failure, depending on the control-board version.

Common causes

• Scaled or restricted heat exchanger
• Soot accumulation
• Improper gas pressure
• Combustion-air restriction
• Burner problem
• Failed stack-flue sensor
• Damaged sensor wiring
• Poor electrical connection

An unusually high exhaust temperature may indicate that heat is not transferring properly from the combustion gases into the pool water. This can occur when the heat exchanger is scaled or water flow is restricted.

Combustion-related testing should be handled by a qualified heater technician.

E01: Open Water-Temperature Sensor

The E01 code generally indicates an open circuit in the water-temperature sensor, also called the thermistor.

Common causes

• Thermistor disconnected
• Broken sensor wire
• Corroded connector
• Failed thermistor
• Control-board connection problem

The thermistor reports water temperature to the heater’s control system. If the circuit is open, the heater cannot reliably regulate the pool or spa temperature.

E02 or Code 126: Shorted Water-Temperature Sensor

An E02 or 126 code generally indicates that the water-temperature sensor circuit is shorted.

Common causes

• Failed thermistor
• Pinched wiring
• Moisture in a connector
• Damaged wire insulation
• Control-board problem

The water-temperature sensor and wiring should be tested before replacing the main control board.

E05: Open Stack-Flue Sensor

The E05 code generally indicates an open circuit in the stack-flue sensor.

Common causes

• Stack-flue sensor unplugged
• Broken sensor wire
• Failed sensor
• Corroded connector
• Loose control-board connection

Because this sensor monitors exhaust temperature, do not bypass it.

E06: Shorted Stack-Flue Sensor

The E06 code generally indicates a shorted stack-flue sensor circuit.

Common causes

• Failed stack-flue sensor
• Pinched or melted wiring
• Water intrusion
• Shorted connector
• Control-board issue

E01, E02/126, E05 and E06 are commonly associated with open or shorted temperature-sensor circuits.

Why Is the Service Heater Light On Without a Code?

Older MasterTemp control panels may illuminate the Service Heater light without clearly showing a full error description on the outside display.

A technician may need to remove the heater panel and inspect the diagnostic lights on the control board. Depending on the model, the internal indicators can identify faults involving:

• PS — pressure switch
• HLS — high-limit switch
• AFS — airflow switch
• AGS — automatic gas-shutoff switch
• SFS — stack-flue sensor

Heater panels should only be removed after electrical power and gas have been safely shut off.

How to Reset a Pentair MasterTemp Heater

A basic reset may clear a temporary fault, but it will not repair the cause of a recurring error.

1. Press the heater-off control.
2. Wait approximately 30 seconds.
3. Restart the pool pump and verify strong circulation.
4. Turn the heater back on.
5. Watch the heater through the complete startup sequence.

If the code returns, avoid continuously resetting the heater. Record the exact code, heater model number and symptoms for the service technician.

MasterTemp Heater Starts and Then Shuts Off

A MasterTemp that lights but shuts down shortly afterward may have:

• Low or unstable water flow
• Dirty filter
• Incorrect gas pressure
• Flame-sensing problem
• Overheating heat exchanger
• Failing thermal regulator
• Internal bypass problem
• Stack-flue temperature problem
• Automation-command issue

Note whether the heater shuts down immediately, after several seconds or after running for several minutes. That timing can help identify which stage of operation is failing.

When You Can Troubleshoot It Yourself

Homeowners can safely check basic external conditions such as:

• Pool-water level
• Pump operation
• Pump speed
• Dirty baskets
• Dirty filter
• Valve positions
• External gas-valve position
• Blocked external air openings
• Visible automation settings

When to Call a Pool-Heater Technician

Contact a qualified professional when the issue involves:

• Gas smell
• Ignition failure that continues after confirming gas supply
• AGS or SFS codes
• Soot or scorch marks
• Melted wiring
• Repeated overheating
• Gas-pressure measurement
• Combustion analysis
• Internal electrical testing
• Safety-switch replacement
• Heat-exchanger scaling or leakage
• Control-board diagnosis

Pentair states that MasterTemp installation and service should be performed by qualified personnel, particularly where gas, electrical and combustion components are involved.

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Frequently Asked Questions

What does ERR PS mean on a Pentair MasterTemp?

ERR PS means the water-pressure switch is open. The most common cause is insufficient circulation through the heater.

What does ERR IGN mean?

ERR IGN means the heater attempted to ignite but did not successfully establish or detect a flame.

What does E05 mean on a Pentair MasterTemp?

E05 generally means the stack-flue sensor circuit is open. The sensor, wiring and connectors should be tested.

Why does my MasterTemp keep showing HLS?

A recurring HLS code commonly points to low water flow, scale, a thermal-regulator problem or an internal bypass problem.

Can a dirty pool filter cause a MasterTemp error code?

Yes. A dirty filter can reduce water flow enough to trigger PS, HLS, AGS or other overheating-related problems.

Can I bypass a MasterTemp safety switch?

No. Safety switches should never be bypassed. They are designed to prevent overheating, combustion problems, equipment damage and unsafe heater operation.

Will replacing the control board fix every error code?

No. Many error codes are caused by water flow, sensors, wiring, gas supply or mechanical heater components. The underlying problem should be diagnosed before replacing the control board.