The short answer
Keep the space around it clear so air flows freely, brush off leaves and snow with the system switched off, and leave cleaning the coil and anything inside the casing to an engineer. Otherwise it needs little beyond its regular service.
The outdoor unit is built to stand in rain, wind, frost and sun for years. What it copes with badly is being starved of air. It works by drawing large volumes of air across its coil, and anything that blocks that flow makes it work harder and can make it stop on its safety controls.
Keep the space around it clear
On most home units, air is drawn in through the coil at the back and side and blown out through the fan grille at the front. The manual sets minimum clearances around the unit, and the installer should have positioned it to allow for them.
- Keep bins, bikes, garden furniture and stored items away from it, and don't use it as a shelf.
- Trim back hedges, shrubs and climbers so they can't grow into the coil or the grille.
- Don't let grass cuttings, leaves or snow pile up against it.
- Keep children and pets from climbing on it or poking things through the grille.
Think before putting up a fence panel, screen or enclosure close to it. It can restrict the airflow, send the unit's own exhaust air back into it, and change how much noise reaches your neighbours, because the noise calculation takes account of nearby walls and barriers. Ask your installer first, and see noise rules and your neighbours. In England, for a unit fitted under permitted development, the size limit of 1.5 cubic metres includes any housing around it. Scotland, Wales and Northern Ireland have their own rules.
Covers
Don't wrap the unit in a full cover while there's any chance it will run. It needs air on every side, and a unit used for heating has to breathe and defrost all winter.
If you want to keep falling leaves or snow off the top, ask the installer about a top guard that leaves the sides and front open and keeps to the manufacturer's clearances.
Cleaning it safely
Switch the system off with the remote before you start, and never reach into the grille: the fan can start without warning.
- Lift leaves, litter and cobwebs off the outside of the coil and grille, or brush them away gently with a soft brush, working along the fins rather than across them and without pressing on them. The fins are thin and can be sharp.
- Wipe the casing with a damp cloth if it's dirty.
- Don't use a pressure washer, a strong hose jet or a stiff brush. The fins bend flat easily, and flattened fins block the airflow.
- Don't remove the casing or any panel.
A proper clean of the coil and fan is part of a service.
In winter
When the system heats in cold, damp weather, frost forms on the outdoor coil and the unit clears it by running a defrost. A whoosh, clouds of steam and a short pause in heating while it does so are all normal.
- Water drips from the unit in heating mode, especially during a defrost. In a freeze it can turn to ice on a path or patio underneath, so grit the spot, and tell the installer if the water drains where people walk.
- Keep snow and ice from building up under the unit, where they can block the drain holes in its base.
- Brush snow off the top and away from the sides without scraping the coil.
- Don't chip ice off the unit or pour hot water over it. Ice that stays after a defrost needs an engineer, as explained in ice on the pipes or outdoor unit.
Some manuals ask for the power to be switched back on at the isolator several hours before the system is used after a long break, to protect the compressor. Check yours before turning a system off at the isolator for months at a time.
Checks through the year
| When | What to look for |
|---|---|
| Spring | Plants growing close, nests, winter debris |
| Summer | Nothing stored in front of the fan |
| Autumn | Leaves on the coil and around the base |
| Winter | Snow around it, ice beneath it |
| Any time | Loose brackets, damaged pipe insulation, new rattles |
The insulation on outdoor pipework can be damaged by sunlight, birds and animals. If you can see bare pipe, or the pipe covers have come loose, have them repaired.
A unit that looks tilted, moves when you touch it or sits on rusting brackets needs checking by an engineer. So does a new rattle or hum that isn't explained by something touching the casing.
Related guides
- What the indoor and outdoor units doThe indoor unit pulls room air through a filter and across a coil that cools or warms it. The outdoor unit holds the compressor that pumps the refrigerant, plus a second coil and fan that release heat outside when cooling and collect it when heating.
- Why the outdoor unit defrosts in cold weatherIn heating mode the outdoor coil runs colder than outdoor air, so in damp weather near or below freezing, moisture freezes onto it. Every so often the system briefly reverses to send heat to the outdoor unit and melt the ice, which is normal.
- Ice on the pipes or outdoor unitA thin layer of frost on the outdoor unit while it heats in cold, damp weather is normal and clears when it defrosts. Ice that stays or keeps building, or that appears while cooling or on the pipes, points to a fault.
- Wall brackets and ground standsWall brackets fix the outdoor unit to a sound wall and keep the ground clear, while ground stands hold it on a firm, level base. Both should raise it clear of water, snow and debris and sit it on anti-vibration mounts.