When should I change air conditioning settings before calling an engineer?

The system feels wrong.
You consider calling for help.
A small check could save the visit.

Many call outs happen when nothing has failed. Settings cause the problem. Knowing what to check first avoids wasted time and unnecessary cost.

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Why settings cause most call outs

Air conditioning systems follow instructions precisely.

Mode selection
Temperature demand
Fan speed
Timers

If one is wrong, the result feels wrong. The system still runs. The room does not improve.

Most winter issues resolve in minutes once settings are corrected.

Start with the operating mode

Mode controls intent.

If the system is in cooling, auto, or fan only mode, heating will not work as expected. Always confirm heating mode shows clearly on the controller.

Look for
The word HEAT
A sun symbol

If you do not see either, change the mode first.

Confirm there is real heating demand

Heating only starts when demand exists.

If the set temperature is close to the room temperature, the system may run gently or not at all. Increase the temperature slightly and wait.

Do not keep changing it.
Make one change and observe.

Allow time before judging results

Heating does not start instantly.

Many systems delay warm airflow to protect internal components. Air may feel neutral or cool for a few minutes. This is normal behaviour.

Wait at least 10 to 15 minutes after changing settings before assuming a problem.

Check fan speed and airflow direction

Fan speed affects comfort.

Low fan speed spreads heat slowly.
Medium fan speed balances warmth better.

Airflow direction matters too. If warm air blows straight up or away from the room, heating feels weak.

Adjust fan speed and airflow before calling for help.

Turn off auto mode for testing

Auto mode complicates diagnosis.

It reacts to short temperature changes and can reduce heating without warning. For testing, switch to heating mode only.

This removes guesswork and shows whether heating can work steadily.

Check for active timers

Timers override manual settings.

They can turn heating off overnight or reduce output during the day. If the system changes behaviour at regular times, a timer is likely active.

Look for a clock symbol on the controller and disable timers you do not need.

Look for signs of normal winter behaviour

Some behaviours look like faults but are not.

Short pauses in airflow
Temporary cool air during defrost
Outdoor unit steaming in cold weather

These are normal winter behaviours for air source systems.

Do not call an engineer for these alone.

Check the obvious room factors

Room conditions matter.

Windows or doors open
Large heat loss from glazing
High ceilings
Open plan layouts

These slow heating and make systems feel ineffective even when working.

Common setting mistakes worth fixing first

These appear repeatedly during winter visits.

Cooling mode left on
Auto mode active
Fan only mode selected
Fan speed too low
Timers still enabled
Multiple controllers set differently

Fixing these resolves most issues.

When changing settings is not enough

Call for support when settings are correct and the problem persists.

Signs include
Heating mode active for over 20 minutes with no warmth
Error codes on the display
No airflow at all
Outdoor unit not running
System shutting down repeatedly

These point to faults rather than usage.

What information helps an engineer

Before calling, note these details.

Model number
Controller type
Mode shown on display
Set temperature
Outdoor temperature
How long the issue has occurred

This speeds up diagnosis and avoids repeat visits.

Related guidance

Further residential air conditioning guidance is available at
https://www.climateworks.co.uk/residential-air-conditioning

References

UK Government guidance on heat pump operation
https://www.gov.uk/guidance/heat-pumps-how-they-work

Building Regulations Approved Document L
https://www.gov.uk/government/publications/conservation-of-fuel-and-power-approved-document-l

ClimateWorks residential service records from installations across Hampshire, Berkshire, Surrey, and Oxfordshire between 2022 and 2025

Author

Dr Julian Carter
Technical and Compliance Director
ClimateWorks

Dr Julian Carter has over 20 years of experience in building services engineering, air conditioning system design, and regulatory compliance. He advises on residential and commercial projects across the UK, covering system selection, installation standards, commissioning, and real world performance.

As Technical and Compliance Director at ClimateWorks, he oversees technical governance, installer training, fault diagnosis, and customer education. His work focuses on reducing user related issues, improving system reliability, and ensuring air conditioning systems perform consistently throughout their service life.

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