Why is my air conditioning fan running but not warming the room?

You hear the fan.
Air is moving.
The room stays cold.

This situation causes a lot of confusion. Many people assume the system is heating because it is running. In reality, the fan can operate without heat for several reasons. Most are linked to settings or normal system behaviour rather than faults.

Why the fan can run without heat

The fan and the heating function are separate.

The fan moves air.
Heating adds warmth to that air.

If heating is not active, the fan can still run and circulate room temperature air. This often makes the space feel colder.

Fan only mode is a common cause

Many systems include a fan only mode.

In this mode
The fan runs
No heating or cooling occurs
Air feels neutral or cool

Fan only mode is easy to select by mistake, especially when cycling through modes quickly.

If the controller shows a fan symbol without HEAT or a sun symbol, heating is not active.

Heating mode may be selected but delayed

Even in heating mode, warm air does not appear instantly.

When heating starts, the system may
Pause airflow
Run the fan slowly
Delay warm air delivery

This protects internal components while the system warms up.

This delay usually lasts a few minutes.

Defrost cycles can stop heat temporarily

In winter, outdoor units can collect frost.

During a defrost cycle
Indoor heating pauses
The fan may continue running
Air may feel cool

This is normal behaviour. Once defrost completes, heating resumes automatically.

Auto mode can remove heat without warning

If auto mode is active, the system may decide not to heat.

Small temperature increases near the sensor can cause the system to reduce heating or switch behaviour. The fan continues to run, but warmth disappears.

For winter use, heating mode provides more reliable results.

Fan speed can exaggerate the cold feeling

High fan speed moves air quickly.

Fast moving air across skin increases heat loss from your body. Even warm air can feel cool when it moves quickly.

Medium fan speed often balances comfort and heat delivery better during winter.

Why standing near the unit feels worse

Airflow near the unit does not represent room temperature.

Standing directly under the unit makes air feel cooler due to movement, not temperature. This leads many users to believe heating is not working when the room is actually warming slowly.

Judge comfort from the centre of the room.

Common user settings that cause this issue

These appear frequently during winter support visits.

Fan only mode selected
Auto mode left active
Heating mode recently selected
Low fan speed slowing heat spread
Timers switching heating off
Multiple controllers set differently

Checking these often resolves the problem quickly.

When the fan running does point to a problem

If the fan runs for over 15 minutes in heating mode with no warmth at all, the issue may not be a setting.

Possible causes include
Low outdoor temperatures limiting output
Sensor faults
Restricted airflow
Installation issues

These require assessment.

When to seek professional support

Contact a specialist if
Heating mode is confirmed with no warmth after 15 minutes
The outdoor unit does not run
Error codes appear
The system cycles on and off

Before calling, note the mode shown, fan speed, outdoor temperature, and how long the issue has been happening.

This helps speed up diagnosis.

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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