Air conditioner not heating: what could be causing it?

You turn on your air conditioner, select a comfortable temperature and wait for the room to warm up. But it stays cold. Is your air conditioner not blowing warm air, producing very little airflow or stopping during heating? Naturally, you will want to know why. Below, you can find out what to check yourself and when it is best to call an engineer. This guide focuses mainly on split air conditioners: systems with an indoor unit and an outdoor unit.

First, check whether your air conditioner can heat

Not every air conditioner has a heating function. If your appliance has never provided heating, check the manual to see whether your model can do so. The remote control must also be compatible with your air conditioner. A heating button on a different or universal remote control does not automatically mean that your appliance supports this function. If your air conditioner has heated properly before, you can move on to checking its settings and maintenance.

Set the air conditioner to the correct mode and temperature

Check that the air conditioner is actually set to HEAT or Heating. Simply increasing the set temperature is not enough if your appliance is still in another operating mode. To test it, select a temperature a few degrees higher than the current room temperature. If the desired temperature has already been reached or nearly reached, the air conditioner may reduce the airflow or stop temporarily. This does not necessarily mean there is a fault. Consider not only whether you can feel air coming out, but also whether the room still needs heating.

Give the air conditioner time to warm up

An air conditioner does not blow warm air immediately after you switch it on. When heating mode starts, the indoor fan may remain still for a few minutes. This prevents the appliance from blowing cold air into the room before the system has warmed up sufficiently. Give the air conditioner time and avoid constantly changing the settings. The length of this start-up phase varies by model. Check the manual to find out what is normal for your appliance.

Heating stops temporarily during defrosting

Does your air conditioner heat at first, but then stop blowing warm air for a while? The automatic defrost function may be active. In cold, damp weather, frost can form on the outdoor unit's heat exchanger. The air conditioner removes this ice automatically, temporarily interrupting heating to do so. The indoor fan may stop, and water vapour may be visible around the outdoor unit. Let the defrost cycle run its course. Heating should resume once it has finished. The message displayed and the time this takes depend on your model and the conditions.

Clean dirty air conditioner filters

If your air conditioner is not heating sufficiently, check the air filters. Dirty filters can restrict airflow. Switch off the appliance, wait for the fan to stop and disconnect it from the power supply in accordance with the manual before you begin. Only remove filters intended for user maintenance. Depending on the filter, you can carefully vacuum away dust or wash it. Important! Not every filter can be cleaned with water. Allow a washable filter to dry completely before putting it back. Follow your manufacturer's instructions; these take priority over general cleaning advice.

Keep the indoor and outdoor units clear

Check whether curtains, furniture or other items are blocking the air inlet or outlet of the indoor unit. Also check that there is enough clear space around the outdoor unit. Leaves or other obstructions can restrict airflow there. Switch off the system and disconnect it from the power supply before removing a blockage. Only deal with anything you can safely reach without opening the appliance. Leave any work that requires grilles to be removed or access to the inside of the unit to an engineer.

Check the operating modes if you have multiple indoor units

If you have multiple indoor units connected to one outdoor unit, check the settings in the other rooms too. With a typical multi-split air conditioner, you cannot cool one room and heat another at the same time. Although you can select a different temperature for each room, the active indoor units must operate in the same mode. Set the units you want to use for heating to heating mode, and consult the manual if a unit does not respond as expected.

The air conditioner blows warm air, but the room stays cold

If warm air is coming from the air conditioner but the room is not reaching the desired temperature, check the airflow, the direction of the outlet louvres and whether any windows or doors are open. The weather can also play a role: when the outdoor temperature is low, the available heating capacity may decrease. This is different from an air conditioner that does not heat at all. If the room remains too cold even though the settings and airflow are correct, have the system assessed to see whether it can provide enough heat under those conditions.

When should you call an air conditioning engineer?

If your air conditioner still does not work properly after these checks, or an error message keeps appearing, note down the message and contact your installer. A fault could, for example, be related to a sensor, the fan motor or the refrigerant circuit. The absence of warm air alone does not tell you which air conditioner part is faulty. Do not replace parts based on guesswork. If you smell burning or an electrical safety device repeatedly trips, stop using the appliance and switch off the power supply if it is safe to do so. 

Always search for air conditioner parts using the model number

If you know that you need a replacement part, search using your air conditioner's full model number. This can be found on the rating plate and is not the same as the serial number. Searching by brand alone or by the shape of the old part is not a reliable basis for ordering. Check the product information to see whether your model is listed and whether the part is genuine or a compatible alternative. This will help you buy the right air conditioner spare parts rather than guessing which filter or remote control will fit.

Maintain and repair before replacing

A heating problem is a good reason to investigate what is wrong first, rather than buying a completely new appliance straight away. Appropriate maintenance or a targeted repair can help you avoid unnecessary replacement. This can save money and reduce the use of new raw materials and the amount of waste. However, consider the whole picture: for an old or inefficient appliance, energy consumption and repair costs also matter. The manufacturer's manual and instructional videos can help with maintenance you are permitted to carry out yourself.

Find compatible air conditioner parts at Fiyo

At Fiyo, you can find air conditioner parts and accessories, such as filters, remote controls and maintenance products. The range includes products for various brands, including DeLonghi, AEG, LG and Whirlpool. Which parts are available and compatible depends on your model. Need help? Our customer service team will be happy to help you find what you need and is available by email, chat and WhatsApp from Monday to Friday. Have the brand and full model number to hand. This will help you order the right air conditioner part for repairing or maintaining your appliance.