Short answer: when a pool heat pump runs but the water barely warms, the cause is usually one of four: low water flow (a dirty filter, a closed valve or a pump that is off), a dirty evaporator coil that cannot take heat from the air, a dirty or scaled titanium exchanger, or low refrigerant. The first two you can check yourself in ten minutes; the last two need a technician. Never open the unit with the power on. A heat pump that is simply too small for the pool or has no cover can also look “broken” when it is only working as designed. We install heat pumps from €2,000 and repair them, and you get the repair price in writing before we start.
First, is it really not heating?
A heat pump heats slowly by design: it moves heat from the air into the water instead of creating it. Before looking for a fault, check three things that explain most complaints:
- The size. A simple rule used by suppliers such as AutoSolar is to divide the pool volume in m³ by 4 without a cover, or by 5 with a thermal cover, to get the power in kW. An 8×4 m pool of about 45 m³ needs roughly 9 to 11 kW. A smaller unit runs for hours and never reaches the temperature.
- The cover. Most heat is lost from the surface at night. Without a cover the pump is heating the sky; Repsol notes a cover reduces heat loss and evaporation, so the heat pump works less.
- The air temperature. The unit loses efficiency when the air falls below about 10 °C, which on the Costa Blanca happens on some winter nights.
If all three are fine and the water still does not warm, look at the symptoms below.
Symptoms and what they usually mean
| What you notice | Most likely cause | Who fixes it |
|---|---|---|
| Fan and compressor run, water warms very slowly or not at all | Low water flow, dirty evaporator, dirty titanium exchanger or low refrigerant | You can check flow and the coil; the rest is a technician |
| Unit does not start, flow or “no water” fault on the display | Filtration pump is off, a valve is closed, or the filter is clogged | You: run the checks below |
| Frost on the fins on a cold, humid night | Normal: the unit defrosts itself | Call only if ice stays on all day |
| Water under the unit | Condensation is normal, because the unit condenses moisture from the air; pool water at the connections is a leaking union | Technician, if it is pool water |
| Error code on the display | Depends on the model | Note the code, read the manual, then call |
| Low pressure on the refrigerant gauge | A refrigerant leak | Technician: topping up without finding the leak means the fault returns |
This is a guide to the usual causes, not a diagnosis. Heat pump manuals typically say the same about safety: switch off the power, do not open the unit, and leave repairs to a technician with original parts.
What you can check yourself (power off)
- The filtration pump is running and the filter is clean. The heat pump only heats while water flows through it, so a clogged sand filter is the first suspect. Habitissimo recommends backwashing at least once a week.
- Valves. The valves to and from the heat pump must be open.
- Mode and set temperature. Some units have heat, cool and automatic modes; check it is on heating and that the target is higher than the current water temperature.
- Air flow. Clear leaves, grass and plants from around the unit and look at the fins from the outside. A blocked coil cannot take heat from the air.
- The breaker. Check it has not tripped.
Repair or replace?
We do not publish a repair price, because refrigerant work, a new exchanger and a cleaned coil are very different jobs. What you can compare: a new heat pump from us costs from €2,000 installed, and Habitissimo gives about €1,700 for the unit alone for a pool of 30 to 55 m³. For a young unit with a small fault, repair is nearly always right; for an old unit with a refrigerant leak and a worn compressor, ask for both figures. Both are given in writing before anything starts.
Running cost matters too. Repsol puts the extra consumption of a pool heat pump at 240 to 1,200 kWh a month, about €40 to €200, with a coefficient of performance between 4 and 7. A unit that is short of refrigerant or has a dirty exchanger works harder for less heat, and the difference shows up on the electricity bill, so a fault left unfixed is not free.
How to keep it working
- Keep the filter clean and the water balanced, since scale and dirt are what clog the exchanger.
- Use a thermal cover at night.
- Have the unit checked once a year before you start heating in spring. Autumn and winter are our quiet months, the cheapest time to book. See our pool maintenance service and pool heating systems.
- Sizing and running costs for a new unit are in heat pump for a pool on the Costa Blanca: price and running cost.
Questions we get asked
Why does my heat pump run all day but the pool stays cold?
Either it is too small for the pool or has no cover, or water flow, the coil, the exchanger or the refrigerant is the problem. Check the filter and the coil first.
Is the frost on the unit a fault?
Not by itself. On cold, humid nights frost forms on the evaporator and the unit defrosts itself. If the ice stays all day, call.
Can I add refrigerant myself?
No. It needs the right gas, gauges and certification, and if the pressure is low there is a leak that has to be found first.
Heat pump not heating? Call +34 634 928 081 or send us the address. The visit is free, and you get the cause and the price in writing. We answer in English, Spanish, Polish and Russian, Monday to Friday, 08:00 to 17:00.
