The Sta-Rite Max-E-Therm is a high-efficiency pool heater with a digitally controlled ignition system. When E05 appears on its LED display, the heater has attempted to establish a burner flame and failed. The unit is in safety lockout. Understanding the Max-E-Therm's specific ignition sequence — which differs slightly from its cousin, the Pentair MasterTemp — is the key to a fast diagnosis.
On a call for heat, the Max-E-Therm control board (sometimes called the IID, Integrated Ignition Device) runs this sequence:
Each step is a potential failure point. Systematic diagnosis starts at step 1 and works forward.
Max-E-Therm tip: The IID board has a small diagnostic LED that flashes codes to indicate which step in the sequence failed. Count the flashes carefully — 2 flashes indicates igniter failure, 3 indicates flame sensor, 4 indicates gas valve. This narrows diagnosis immediately.
The HSI glows orange-white to ignite the gas. A cracked or end-of-life igniter won't reach temperature. Check by visual inspection (any crack = replace) and resistance measurement (should read approximately 50–100 ohms at room temperature for a silicon carbide HSI). Max-E-Therm OEM igniter: Sta-Rite part 42001-0052S or equivalent.
The flame rod produces a small rectified current (1.5–5 microamps) when in contact with the ionized gas flame. A film of oxidation on the rod increases resistance and drops the signal below the board's detection threshold. Clean the rod with 400-grit emery cloth — not steel wool which leaves particles. The rod should come clean with a few passes. If it's deeply pitted or eroded, replace it.
Use a manometer to measure supply pressure at the gas valve inlet. Minimum for natural gas: 4" WC (some models need 5" WC — check the rating plate). Minimum for propane: 11" WC. Low pressure is common when: the meter regulator is aging and undersized, when multiple gas appliances run simultaneously, or with long propane tank runs on cold days (propane vapor pressure drops as tank empties in cold weather).
This is a Max-E-Therm specific note that applies to any heater sitting unused for a season: mud dauber wasps, spiders, and yellow jackets frequently nest inside the burner tubes and gas orifice openings. Even a partial nest can prevent gas from reaching the igniter area. Remove the access panel, inspect the burner assembly carefully, and clear any nests before first-of-season operation.
The gas valve requires 24V AC to open. Test voltage at the valve terminals during ignition trial. If voltage is present and the valve doesn't open (no audible click, no gas smell), the valve has failed. Max-E-Therm uses a combination gas valve that is model-specific — always order by full model number.
After ruling out all hardware, the IID board itself may be failing. This is uncommon. Before condemning the board, verify every output voltage with a multimeter during a heat call. IID boards are expensive ($150–300) — confirm the diagnosis thoroughly before ordering.
| Code | Meaning | First Check |
|---|---|---|
| E05 | Ignition Failure | Igniter, flame sensor, gas supply |
| E01 | High Limit Fault | Flow rate, filter |
| E02 | Stack Hi-Limit Fault | Flue obstruction, scaling |
| E03 | Pressure Switch Open | Blower, pressure switch hose |
| E04 | Water Temperature Sensor | Inlet NTC sensor and wiring |
Warning: If you smell gas strongly near the heater during or after failed ignition attempts, shut off the gas supply valve immediately and ventilate the area before any further work. Do not operate electrical switches near a gas smell.
Look up Max-E-Therm error codes and IID diagnostic LED patterns in SplashLens — available offline when you're standing at the equipment pad.
SplashLens covers Max-E-Therm, MasterTemp, and all Pentair heater error codes. Free, no login, works without cell service.
Open SplashLens Free →E05 on the Sta-Rite Max-E-Therm is an ignition fault — the control board attempted to light the burner but did not detect a flame signal within the ignition trial period. The heater locks out after 3 failed attempts.
Yes and no. The Max-E-Therm and MasterTemp share similar technology and are both made by Pentair. However, they are separate product lines with different model numbers, some different parts, and slightly different control boards.
Press and hold the Mode button for 3 seconds to clear the fault. If the heater is in hard lockout after multiple attempts, power-cycle at the breaker. Always fix the root cause before resetting.
The flame sensor on the Max-E-Therm is a thin metal rod (approximately 6 inches long) that extends into the burner flame area. It connects to the control board via a single insulated wire.
Yes. Insects (especially mud daubers and wasps) are known to nest inside gas valve orifices and burner tubes during off-season storage. Inspect and clear the gas manifold and orifices if the heater has sat unused for months.