AquaCal Heat Pump Codes: FS, HP, LP & More Explained

This guide explains the fault codes on AquaCal heat pumps — HeatWave SuperQuiet, TropiCal, and related models — what each one means, and the safe checks to try before calling. We're the Pinellas County company licensed for the electrical side of these repairs (EC13011994, CPC1459998), with St. Pete-built AquaCal units all over our service area.

FLO — Low or No Water Flow

The heat pump isn't seeing enough water moving through it, so it shuts down to protect itself. Per AquaCal's SuperQuiet documentation, these units want roughly 30–70 GPM — so the usual causes are the filter pump being off or a variable-speed pump running too slow, a dirty filter or full baskets, or valves diverting water around the unit.

• Run the filter pump on high speed.
• Empty the skimmer and pump baskets; clean or backwash the filter.
• Verify the valves are sending water through the heat pump.

FS — Unit Calls for Heat but Won't Run

AquaCal's own troubleshooting guidance describes FS appearing when the fan doesn't start on a call for heat — shown after the compressor starts. Exactly which sensor FS names varies by control-board revision, but either way it's a no-run condition: the likely causes are a fan motor problem, a fan obstruction, or a switch/board fault.

• Look — don't reach: is the top fan spinning when the unit calls for heat?
• With the unit OFF, clear leaves and debris from the top grille.

HP — High Refrigerant Pressure

The high-pressure switch opened because refrigerant head pressure climbed too high. In heating mode this is almost always the water side failing to carry heat away — low water flow from a dirty filter or low pump speed, valves bypassing the unit, or an external bypass set outside the 30–70 GPM window.

• Do the same water-flow checks as FLO: pump on high, clean baskets, clean filter, correct valve positions.
• Check your filter pressure gauge — 7–10+ psi over its clean baseline means the filter is choking flow.

HP5 — High-Pressure Lockout

Five consecutive HP faults in one heating or cooling cycle — the unit has locked itself out because the underlying high-pressure cause was never fixed. This is the heat pump protecting its compressor.

• Power off at the breaker, restore full water flow (filter, baskets, valves), then power on once.
• If it locks out again, leave it off.

LP — Low Refrigerant Pressure

The low-pressure switch opened because refrigerant suction pressure dropped too low. In heating mode that means the air side isn't feeding enough heat into the unit: the fan isn't running, airflow is blocked by shrubs, fences, or debris on the coil, the coil has iced over on a cold night — or the unit is genuinely low on refrigerant from a leak.

• Clear at least 24 inches of open space around the unit.
• With the power OFF, gently rinse leaves off the coil with a garden hose.
• Look for ice on the coil — if it's iced, leave the unit off and let it thaw.

LP5 — Low-Pressure Lockout

Five consecutive LP faults in one cycle. When a low-pressure lockout keeps returning after airflow is cleared, the underlying cause is often an actual refrigerant leak — which no amount of resetting will fix.

• Clear the airflow (space around the unit, clean coil, no ice), then power cycle once.
• If it locks out again, leave it off.

dPo / dPc — Defrost Sensor Open or Shorted

The defrost sensor — the thermistor that tells the board when to run a defrost cycle — is reading open (dPo) or shorted (dPc). That usually means a failed thermistor or chafed, corroded sensor wiring, something Pinellas salt air accelerates.

• Power-cycle the unit once at the breaker.

PO / PC — Water Temperature Sensor Open or Shorted

Same failure pattern as dPo/dPc, but on the water-side temperature sensor: PO is an open reading, PC a shorted one. A failed thermistor or damaged wiring is the usual cause.

• Power-cycle the unit once at the breaker.

CEr — Communication Error

The display and the control board have stopped talking to each other — typically a loose, corroded, or damaged communication cable, or less often a failed display or board.

• Power-cycle the unit once at the breaker.

CSE — Control System Error

An internal controls fault — often the aftermath of a power glitch, sometimes a genuinely failed board. A clean restart is worth one try.

• Power off at the breaker, wait 1–2 minutes, then restart.
• If the code returns, leave it off.

OtA — Incoming Water Over 110°F

The unit locked out because incoming water measured above 110°F. Real-world causes: a gas heater plumbed upstream is overshooting, a very hot return line, or a sensor error.

• If you also have a gas heater, check whether it's set (or stuck) far hotter than intended.
• Power-cycle the heat pump once.

"Defrost" on the Display — Not a Fault

On a cold night (typically below ~50°F air temperature), the unit pauses heating and runs a defrost cycle — the fan and compressor behavior changes, and that's normal. Just wait it out.

• No action needed. If it seems to defrost constantly in mild weather, note it — that pattern suggests low refrigerant, which is a professional diagnosis.

Why Homeowners Across Pinellas Call Us for AquaCal Heat Pumps

• Licensed electrical contractor (EC13011994): fan motors, sensors, comm cables, and control boards — most AquaCal codes that aren't flow problems end in electrical repair, and components inside can hold a charge even with power off.
• Refrigerant-circuit discipline: HP/LP lockouts often trace to the sealed refrigerant circuit — EPA-certified territory where DIY attempts destroy compressors. We diagnose it properly instead of reset-spamming it.
• Licensed pool contractor (CPC1459998): the #1 trigger for FLO and HP codes is the pool system itself — filter, pump speed, valves — and we service that whole loop on the same truck.