Heat pump hot water not hot enough
Check the steps below first — if you're not confident, get it fixed safely today.
Post a job — we'll find you an engineer →⚠️ Domestic hot water must reach at least 60°C periodically to prevent Legionella bacteria growth. Never permanently disable the cylinder Legionella protection cycle.
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Most likely cause & what to check
Heat pumps are less efficient at heating water to the 60°C that a gas boiler easily achieves. Most ASHP systems heat the hot water cylinder to 50–55°C via the heat pump, with a periodic boost to 60°C using the cylinder's immersion heater element. If your hot water feels cool, this is usually a settings issue.
Check the target temperature on your cylinder thermostat or heat pump controller — it should be set to at least 50°C for daily use. Some controllers default to 45°C for efficiency, which many people find too cool for comfortable showering.
Check when the hot water cycle runs. Most ASHP systems heat water once per day (often at night or in the morning). If multiple people shower in succession, the cylinder may be depleted before it reheats. Ensure the cylinder is large enough — for a family of 4, a 250-litre cylinder is the minimum for an ASHP system.
Enable or check the Legionella protection cycle. This should run the immersion heater to bring the cylinder to 60°C at least once per week. If this has been disabled (for efficiency), the water will be safer but may feel cooler day-to-day as the target temp is often kept lower without it.
If the heat pump is running the hot water cycle but not reaching target temperature, check the hot water heat exchanger coil inside the cylinder — on an ASHP system this should be a large coil near the bottom of the cylinder (a dedicated ASHP cylinder). An undersized coil forces the heat pump to run inefficiently.
If the immersion heater is the backup for the Legionella cycle, check it is working. Immersion heaters fail over time (mineral scale on the element). Test by manually triggering the Legionella cycle and monitoring whether the cylinder reaches 60°C. If not, the immersion element may need replacement (£40–£100 part, straightforward for an electrician).
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