Pentair MasterTemp ERR IGN: Ignition Control Module Failure

What ERR IGN Actually Means

The MasterTemp uses a hot surface igniter (HSI) instead of a standing pilot or spark ignition. During a normal firing sequence, the control board confirms air flow (AFS switch closes), then energizes the HSI element for a warm-up period. Once the HSI reaches ignition temperature, the gas valve opens and the ignition control module looks for flame current through the flame sensor. If flame is not detected within the trial-for-ignition window, the module shuts the gas valve and reports ERR IGN.

This is a safety lockout. Unburned gas in the combustion chamber is a serious hazard. The control will not retry automatically after ERR IGN. You must manually clear the error by pressing HEATER OFF on the membrane pad. After multiple failed attempts, a full power cycle (turning the heater off at the breaker and back on) may be required.

ERR IGN can result from problems anywhere in the ignition chain: the HSI element, gas supply, gas valve, ignition control module, flame sensor, or wiring between these components.

Step-by-Step Troubleshooting

Owner-Level Checks

Confirm gas supply

1. Verify the gas shutoff valve upstream of the heater is fully open.
2. If the heater is on propane, check the tank level. An empty or nearly empty tank will not supply adequate pressure.
3. Check if other gas appliances in the area are working. If nothing else fires either, the problem is upstream of the heater.

Listen and watch the startup sequence

1. When you call for heat, listen for the blower to start, then look through the sight glass for the HSI to glow orange.
2. If the HSI glows and you hear gas release but no ignition, the igniter may be too weak or the gas pressure may be wrong.
3. If the HSI does not glow at all, the igniter element or its power circuit has failed.

Tech-Level Checks

Inspect the HSI igniter

1. Power off the heater. Remove the burner access panel and locate the HSI element near the burner tray.
2. Look for visible cracks, chips, or white discoloration on the silicon carbide or silicon nitride element. Any physical damage means replacement.
3. Measure resistance across the HSI terminals with a multimeter. An open circuit or extremely high resistance means the element is burnt out. Refer to the igniter manufacturer's specs for the expected resistance range.

Check HSI voltage during startup

1. Restore power and initiate a heat call. Measure voltage at the HSI connector during the warm-up period.
2. You should see approximately 120VAC at the igniter. If voltage is present but the HSI does not glow, replace the igniter.
3. If no voltage reaches the HSI, suspect the ignition control module or the wiring harness.

Test the flame sensor

1. The flame sensor is a small rod that sits in the flame path. It detects flame by measuring current through the flame to ground.
2. Clean the flame sensor with fine emery cloth or steel wool. Carbon buildup insulates the rod and prevents flame detection even when flame is present.
3. If you have a microamp meter, measure flame current in series. Low or zero current with flame present confirms a dirty or failed sensor.

Check gas pressure

1. Connect a manometer to the gas valve test port. Check incoming pressure and compare to the rating plate. The MasterTemp requires minimum 4" WC inlet pressure for both Natural Gas and Propane, with a maximum of 14" WC.
2. The MasterTemp uses an unconventional negative-pressure gas valve. Manifold pressure should read -0.2 ± 0.1" WC. All readings must be taken while the heater is operating.
3. If inlet pressure is low, the gas line may be undersized, the regulator may be failing, or there is a restriction upstream.

Evaluate the ignition control module

1. If the HSI works, gas pressure is correct, the flame sensor is clean, and you still get ERR IGN, the ignition control module itself may have failed.
2. Check all wiring connections to the module for corrosion or loose pins.
3. Replace the module if all other components test good.

Common Parts That Fix This Problem

• Hot surface igniter (HSI) element
• Flame sensor rod
• Ignition control module
• Gas valve (if it fails to open or has erratic operation)
• 12-pin wiring harness (if connections are corroded)

Model-Specific Notes

• All MasterTemp models use HSI ignition. There is no standing pilot on any model in the MasterTemp line.
• The manual's troubleshooting flow chart "Heater Will Not Fire - B" covers the blower, gas flow, HSI igniter, flame current, gas valve, and ignition control module sequence. Follow it step by step.
• Natural Gas and Propane models use different gas orifices and regulator settings. Verify the heater matches the gas type being supplied. A NG heater on LP (or vice versa) will not ignite reliably.
• On the 12-pin plug connector, the red wire carries 240V and the black wire carries 120V. Verify correct line voltage at this connector as part of the "Heater Will Not Fire - A" flow chart.

How to Prevent ERR IGN From Coming Back

• Replace the HSI igniter proactively if it shows hairline cracks or has been in service for several years. They are wear items.
• Clean the flame sensor once per season during routine heater maintenance.
• Verify gas pressure at startup each season, especially after any gas line work in the area.
• Keep the burner tray and combustion chamber clean so flame can reach the sensor reliably.
• Protect electrical connections from moisture and corrosion, especially on outdoor installations.