Aqua-Hot AHE-250-D03 error code D4 LED NEVER ILLUMINATES
On the AHE-250 relay control board the indicator LEDs are D1 Heating Status (orange), D2 Electric Element Power (green), D3 Pump Power (blue), D4 Low-Temperature Cutoff Status (yellow), D5 Burner Status (green), D6 Interior Zone Heating (orange) -- there is NO 'flame-proof' D-LED. If D4 (Low-Temperature Cutoff Status) never illuminates, the low-temperature cutoff thermostat circuit is open/not signaling. Flame on the 250 is proven by the PHOTO-EYE (a separate component, not a D-LED); for a no-flame condition see 'BURNER FAILED TO IGNITE'.
What to check, and in what order, is in the app. The flow Aqua-Hot — Diesel Burner Won't Ignite walks this code step by step with the pass/fail measurements, wiring schematics and procedures that go with it, and it works offline in the bay.
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- Aqua-Hot 200-Series 250P/250D Service ManualAqua-Hot
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