Air source heat pump not heating water: causes and fixes

If your heat pump is keeping the house warm but your hot water has gone cold, the fault is usually in how the system switches between heating and hot water, not the heat pump itself. Here are the usual suspects we find on call-outs across Edinburgh and East Lothian.

Check the basics first

Confirm the cylinder thermostat is set correctly and any hot water schedule or boost is actually on. A surprising number of no-hot-water calls come down to a timer or holiday mode left switched off after a power cut.

Diverter valve and cylinder

Most systems use a diverter valve to send heat to the cylinder. If it sticks, the heat pump heats radiators but not water. A failed immersion backup or a faulty cylinder sensor can cause the same symptom.

Controls, refrigerant and when to call us

Controls faults and low refrigerant can both stop hot water production. These need an engineer with the right tools. We diagnose the exact cause and give you a fixed price before any work.