Heat Pump First Winter Expectations UK 2026

1. Outdoor unit runs 16-22 hours/day in cold weather. Heat pumps deliver heat continuously at low output (vs gas boiler bursts). Long run-times are correct + efficient. Run-time only becomes a concern if indoor temperature isn't reaching target despite the heat pump running.
2. Periodic defrost cycles + visible water dripping. Every 30-90 minutes in damp +2-5°C weather, the heat pump briefly reverse-cycles to clear frost off the outdoor unit. Water drips from the unit during + after defrost - normal + by design.
3. Bills 5-15% higher than installer estimate. Real-world SCOP is typically 85-95% of installer's calculation due to commissioning variations + property-specific factors. Within ±15% of estimate is normal.
4. Occasional auxiliary electric heater activation. During cold snaps (below -5°C) the backup electric heater may briefly fire to assist. 1-5 days/year of aux activation is normal; daily reliance is not.
5. Slightly cooler indoor temperatures in cold weather (1-2°C below target). Acceptable thermal-comfort lag during cold snaps as the property's thermal mass equilibrates. Sustained 3+°C below target indicates a real problem.

1. Indoor temperature consistently 3+°C below target for multiple days. Either undersized heat pump, weather compensation curve wrong, or hydronic system fault. Genuine installer issue.
2. Fault codes displayed on the controller (E04, E12, similar). Manufacturer-specific codes indicate sensor or hardware faults. Call installer or check manufacturer app for fault meaning + recommended action.
3. Very loud or persistent compressor noise. Heat pumps make a quiet whoosh + occasional defrost-cycle sounds. Loud knocking, grinding, or rapid clicking = something wrong. Don't ignore.
4. Bills 30%+ above installer estimate. If your January bill is double the estimate, something's wrong - undersized unit, weather comp disabled, aux heater stuck on, or measurement error. Investigate.
5. Hot water frequently insufficient. If you're running out of hot water during normal household usage, the cylinder coil sizing is wrong OR the heat pump's hot-water reheat priority isn't configured correctly. Installer issue.

Week 1-4 after commissioning: hands off the controller settings. Let the property's thermal mass + the heat pump's weather compensation find their natural operating points. Specifically:

• Don't adjust the weather compensation curve. Installer defaults are reasonable + your observations need a full month's data to identify whether they need tuning.
• Don't tweak temperature setpoints daily. Pick a target temperature (typically 19-21°C) + leave it; the heat pump optimises around a stable target far better than a moving one.
• Don't compare bills to gas-boiler-era bills. The first month may include partial-month effects + transition costs that aren't representative. Wait for the full month's electricity bill.
• Do note unusual events: any fault codes, persistent cold rooms, hot water shortages, very loud noise. Photograph or screenshot if possible.

Week 5-8: start active monitoring without changing settings yet:

• Daily room temperature log: 2 main rooms, morning + evening + bedtime, with outdoor temperature.
• Weekly electricity meter readings: note total + estimate the heat pump portion.
• Manufacturer app data: if your heat pump app exposes SCOP, run-time, fault history - check weekly + screenshot.
• Comfort observations: any rooms running too cool or too warm at specific times.

By end of month 2 you'll have ~30 data points + clear patterns. Use this to drive month-3 tuning decisions.

Week 9-12: act on what you've learned:

• If everything's working well: no action needed beyond annual service scheduling. Heat pump has bedded in.
• If specific rooms run too cool / too warm: adjust the weather compensation curve per our weather compensation guide. Small changes (±0.1 slope, ±1°C offset) make meaningful differences.
• If short-cycling is observed: apply fixes from our short-cycling guide - typically weather-comp adjustments + controller anti-cycle settings.
• If 'not normal' symptoms persist: call installer with your 2-month log. Specific data (room temps + bill spikes + fault codes) gets you faster + better diagnosis than 'something feels wrong'.