Why controls matter more than with a boiler
A gas boiler can heat a cold house quickly by burning gas hard and sending very hot water round. A heat pump can also run harder, but every degree of extra flow temperature costs efficiency. So the habits that suit a boiler, heating hard for an hour in the morning and an hour in the evening, push a heat pump into its least efficient way of working. The controls are there to keep it in its efficient range: a low flow temperature, running steadily.
Weather compensation
Weather compensation uses an outdoor temperature sensor to set the flow temperature. On a freezing day it sends warmer water; on a mild day, cooler water. The relationship between the two is called the heating curve. Most of the UK heating season is mild rather than freezing, so a well-set curve keeps the flow temperature low most of the time, which is where the efficiency comes from.
Setting the curve is part of commissioning. If the house is too warm on mild days, the curve can come down; if it struggles on cold days, it can go up at that end. Small adjustments in the first winter are normal.
Schedules and setbacks
Many heat pump owners leave the heating on through the day at a steady temperature, perhaps with a slightly lower setting overnight. Turning the system off for long periods lets the building cool, and getting it back to temperature needs a high flow temperature for a while, which is inefficient. A setback, a lower target rather than off, is often the better compromise. How much setback suits a home depends on how quickly it loses heat.
Room thermostats and zones
A heat pump can be controlled by room temperature as well as weather compensation. What it should avoid is an on-off thermostat that repeatedly stops and starts the compressor. Many systems run best with most radiators left open, so water flows freely, rather than with lots of separately switched zones. Thermostatic radiator valves can still trim individual rooms, such as a bedroom kept cooler.
What poor controls cost
Field trials show how wide the spread is between similar heat pumps in similar homes. The Electrification of Heat trial's interim median for air source systems was 2.80, with installations either side of it; flow temperature and control settings are among the reasons. In money, the step from an efficiency of 2.5 to 3.0 changes the price of a kWh of heat from 10.53p to 8.77p at the price cap for 1 October to 31 December 2026.
Tariffs and smart controls
Some electricity tariffs charge less at certain times. Smart controls can shift some heating, or heating the hot water cylinder, into cheaper periods, using the building and the cylinder as a store. That can lower the bill even if it slightly lowers efficiency. The tariffs guide covers the trade-off.
A short checklist after installation
- Ask the installer to show you the heating curve and how to adjust it.
- Agree a schedule: steady, with gentle setbacks, rather than on-off.
- Check when the hot water cylinder heats and when the hygiene cycle runs.
- Note the backup heater settings, and ask what would make it run.
- After a few weeks of cold weather, review comfort and adjust the curve.
Holidays and long absences
For a long absence in winter, most systems have a frost-protection or holiday mode that keeps the home at a low temperature and stops the hot water heating, rather than switching everything off. That protects pipes and makes the return to normal temperature gentler. Check how your controls handle hot water on the day you come back, as the cylinder may need a few hours to reheat.