Pentair Pool Heater ERR IGN, ERR AGS, and ERR HLS — Ignition, Gas Shutoff, and High Limit Guide

Error Code: Pentair ERR IGN, ERR AGS, and ERR HLS

What it means: These three Pentair error codes cover different failure modes on MasterTemp and MiniMax pool heaters. ERR IGN means the heater tried to light the burner but detected no flame. ERR AGS means the automatic gas shutoff valve closed due to an unsafe condition. ERR HLS means the high limit switch tripped because water temperature exceeded the safe threshold. Each code has distinct causes and reset procedures. In some cases one code can cascade into another.

Common Causes

ERR IGN (Ignition Failure)

• Gas supply off — Propane tank empty, natural gas valve closed, or gas pressure regulator malfunction.
• Spark electrode issue — Electrode cracked, gap too wide or too narrow (should be 1/8 inch or 3mm), or high voltage lead damaged.
• Flame sensor dirty — Carbon or oxide buildup on the flame rod prevents detection of the rectified flame current.
• Gas valve solenoid failure — Solenoid does not open when control board sends 24VAC. Coil resistance out of range.
• Control board failure — Board fails to generate spark or signal the gas valve.

ERR AGS (Automatic Gas Shutoff)

• High inlet gas pressure — Pressure exceeds the gas valve rated capacity, causing the internal safety to close.
• Internal gas valve failure — Valve mechanism stuck or seal compromised.
• Gas pressure regulator malfunction — Failed regulator sends incorrect pressure to the valve.
• Multiple failed ignition attempts — ERR IGN occurring repeatedly can trigger ERR AGS as a secondary safety.

ERR HLS (High Limit Switch)

• Low water flow — Dirty filter, closed valve, blocked skimmer, or pump not fully primed.
• Stuck bypass valve — Internal thermal regulator bypass stuck in the open position. Water bypasses the heat exchanger, causing uneven heating and local hot spots.
• Heat exchanger scaling — Calcium buildup restricts internal water flow through the heat exchanger tubes.
• Bad high limit switch — Switch fails closed (welded contacts) or opens at too low a temperature. Switch is normally closed and opens at its rated temperature (typically 135 to 150F).

Step-by-Step Fix

FOR ERR IGN (Ignition Failure)

1. Check the gas supply. Confirm the gas valve is fully open. For propane systems, check the tank level gauge. For natural gas, verify the meter is active and the shutoff valve is in line with the pipe.

2. Inspect the spark electrode. Remove the spark electrode assembly from the burner tray. Check for cracks in the ceramic insulator. Measure the spark gap. It must be 1/8 inch or 3mm. If the gap is wrong, bend the electrode tip carefully. Replace the electrode if the ceramic is cracked.

3. Clean the flame sensor. The flame sensor is a metal rod mounted near the burner. Remove it and clean the surface with fine emery cloth or 220-grit sandpaper. Do not use steel wool. Steel wool leaves debris that creates a partial short. Reinstall the sensor and retry ignition.

4. Test the flame sensor current. Put a microamp meter in series with the flame sensor wire. With the burner running, you should see 2 to 6 microamps DC. Below 1.5 microamps will cause intermittent ignition failure. Replace the sensor if cleaning does not restore current.

5. Test the gas valve solenoid. With the heater calling for heat, measure voltage across the gas valve solenoid terminals. You should see 24VAC. If voltage is present but the valve does not open, measure coil resistance. Typical values are 20 to 50 ohms. An open circuit means the solenoid is failed.

6. Reset the control board. Power cycle the heater at the breaker. Wait 60 seconds, then restore power. If the board has a red diagnostic LED, count the flash pattern. That pattern gives additional diagnostic codes beyond the display.

FOR ERR AGS (Automatic Gas Shutoff)

1. Do not repeatedly reset this code. ERR AGS means the internal gas valve detected an unsafe condition. Forcing repeated resets without diagnosis can cause unsafe gas accumulation.

2. Check gas inlet pressure. Use a manometer at the inlet pressure tap on the gas valve. For natural gas, inlet pressure should be 5 to 7 inches WC with the heater off and at least 5 inches WC with the heater on. For propane, inlet pressure should be 11 to 13 inches WC.

3. If inlet pressure is high, adjust or replace the gas pressure regulator. The regulator is typically on the gas line before the heater, not on the heater itself.

4. If inlet pressure is correct, the gas valve may need replacement. Internal valve failures cannot be repaired. Replace the entire valve assembly.

5. Manual reset. Some Pentair gas valves have a manual reset button on the valve body. Locate the red or black button and press it firmly. If the valve trips again immediately, do not reset it again without diagnosis.

FOR ERR HLS (High Limit Switch)

1. Check water flow first. High limit switches trip because the heat exchanger overheats. Low flow is the most common cause. Clean the filter, open all valves, prime the pump, and check the skimmer basket.

2. Test the high limit switch. With power off, disconnect the high limit switch wires. Set your multimeter to continuity mode. Place probes on the two switch terminals. The switch should show continuity (near zero ohms) at room temperature. If it shows open circuit at room temperature, the switch is failed open and needs replacement.

3. Check the thermal regulator bypass valve. The bypass valve is located in the plumbing between the inlet and outlet of the heat exchanger. If it is stuck open, hot water recirculates through the exchanger without going to the pool. This causes the HLS to trip because the exchanger temperature rises quickly while the pool water stays cool.

4. Inspect the heat exchanger for scaling. Remove the exchanger end caps or look through the service ports. White or tan deposits on the tube walls indicate calcium scaling. Use a commercial descaling solution designed for pool heaters. Follow the product instructions carefully. Acidic descaling solutions can damage the exchanger if left too long.

5. Reset the HLS. Once the water is flowing correctly and the heater has cooled (wait 10 minutes), press the red reset button on the high limit switch. The reset button is located on the switch body inside the front panel. On MasterTemp heaters, you can also press POOL/SPA then ON on the touchpad to reset.

Parts That May Need Replacement

Technician Tips

When you see ERR HLS, check the thermal regulator first. A stuck open bypass valve causes HLS trips that no amount of filter cleaning will fix. The bypass is the most overlooked component in Pentair high limit calls.

For ERR IGN, pay attention to the timing. A heater that lights then loses flame after 2 to 3 seconds has a flame sensor problem. A heater that never produces a spark has a control board or spark electrode problem. A heater that sparks but never lights has a gas supply problem.

ERR AGS is rare but serious. If you see it, run a full gas pressure test before doing anything else. High inlet pressure from a failed utility regulator can damage the gas valve. Call the gas utility to check their regulator before replacing the heater valve.

The MasterTemp diagnostic touchpad can show secondary information. After the error code appears, press the POOL/SPA button then ON. The display may show additional diagnostic information or code numbers depending on the firmware revision.

Need Replacement Parts?

Finding the right replacement parts for your Pentair heater is critical. Check current prices on Amazon. Prices and availability change frequently.

When to Call a Professional

If you have cleaned the flame sensor, verified the spark gap, confirmed gas supply pressure, and the ERR IGN code returns after every reset cycle, call a pool heater technician. The issue is likely a failed control board or gas valve that requires OEM-level diagnostics.

For ERR AGS, call a professional immediately. This error indicates a potential gas valve or pressure regulator failure. Gas safety components should not be serviced by untrained personnel. The gas utility may also need to inspect their supply regulator.

For ERR HLS, call a professional if the high limit switch trips repeatedly after you have cleaned the filter, confirmed pump flow, and reset the switch. A cracked heat exchanger or severely scaled exchanger will require heater disassembly.

Tell the tech which error code you are seeing, what you have already checked, and whether the heater has had prior leak repairs or gas line work.

See Also

• Pentair MasterTemp ERR PS — Pressure Switch Failure Guide
• Hayward Pool Heater IF Code — Ignition Failure Troubleshooting
• Pool Heater Ignition Failure — Cross-Brand Troubleshooting Guide

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• Hayward Pool Heater IF Code — Ignition Failure Troubleshooting
• Pool Heater Ignition Failure — Cross-Brand Troubleshooting Guide
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