Aqua-Hot error code LOW TEMP CUTOFF ACTIVE
Low-Temperature Cutoff STATUS active (D4 indicator). Per the 200-Series Service Manual the LTCO status thermostat deactivates interior heat when domestic hot water is being used (DHW priority) and activates the stir pump; the light is on when there is a demand for hot water OR the Aqua-Hot is not yet up to operating temperature. This is a STATUS indicator, not a low-temperature safety lockout.
What to check, and in what order, is in the app. The flow Aqua-Hot — Fluid Level Check & Refill Procedure 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
- Aqua-Hot Heating Systems Service Manuals — aquahot.com
- Aqua-Hot Tech Support 800-685-4298 (Fort Lupton, CO)
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