The short answer
Commissioning is the set of tests that prove a new system is sealed, safe and working as designed. Handover is when the engineer shows you how to use and look after it and gives you the records and certificates to keep.
On this page
Commissioning is where a good installation proves itself. It's also the part most easily skipped, because a system can seem to work perfectly on the day even when a step has been rushed. The records you receive are your evidence that the work was done properly.
What commissioning checks
Some checks happen before the refrigerant is released into the pipes, and others once the system is running. The order they fit into the day is described in what happens on installation day.
| Check | What it shows |
|---|---|
| Pressure test with nitrogen | The pipework and joints don't leak |
| Vacuum and hold test | Air and moisture are out, and it stays sealed |
| Refrigerant charge | The right amount, including any added |
| Leak check after the charge | Joints are sound with refrigerant in them |
| Electrical tests | The circuit is safe and correctly protected |
| Test run in cooling and heating | The system cools, heats and responds properly |
| Drain test | Water runs away freely |
The test run
With everything connected, the engineer runs the system in cooling and heating. Typical checks include:
- the air leaving the indoor unit is suitably colder or warmer than the air going in
- the outdoor unit starts, runs smoothly and switches between modes
- neither unit makes unusual noise or vibration
- no error codes show on the unit or the controls
- the louvres, fan speeds, remote control and any app respond properly
- water poured into the drip tray drains away
Some engineers also compare the system's pressures and temperatures with the manufacturer's figures. Valve caps on the outdoor unit should be refitted and tightened, and the hole through the wall sealed inside and out.
The handover
Before the engineer leaves, you should be shown how to:
- switch the system on and off, set the temperature and choose a mode
- use the timers, sleep or quiet settings and any app
- adjust the fan speed and the direction of the airflow
- remove, clean and refit the filters
- find the isolator switch, if one is fitted
A good handover also explains what's normal, so it doesn't worry you later:
- In heating mode the outdoor unit pauses now and then to defrost, and may give off a cloud of steam.
- Water dripping from the outdoor unit in heating mode is expected.
- Soft clicks and a faint sound of flowing refrigerant when the system starts or stops are normal.
- When heating starts, the indoor fan may wait a few minutes until the coil is warm, so it doesn't blow cold air.
For more on the controls, see the modes explained. Filter cleaning is covered step by step in how to clean the filters.
Records you should get
| Document | What it shows |
|---|---|
| Commissioning record | Test results, refrigerant type and amount |
| Electrical Installation Certificate | How the new circuit was installed and tested |
| Building regulations certificate | The electrical work complies (England and Wales) |
| Noise calculation | The outdoor unit meets MCS 020(a) |
| Manuals and warranty details | How to use it and what's covered |
A useful commissioning record also lists the model and serial numbers of both units, the date, the engineer's name and the installing company's F-gas certificate number. The system itself should carry a label showing the type and amount of refrigerant it contains.
If you applied for planning permission or a Lawful Development Certificate, keep that too. Store everything together: it helps with warranty claims, future servicing and selling your home.
Looking after it from day one
Manufacturers typically recommend regular servicing, often yearly, and some warranties depend on it. Some also need the warranty registering within a set time of installation, so check whether the installer does that or you need to. What a visit involves is set out in what a service involves.
Filters usually need cleaning every few weeks while the system is in regular use.
Before the engineers leave, look over the work. Pipe covers should be fitted and secure, the hole sealed, and the work areas left clean. Point out anything you're unsure about while they're still there to deal with it.
Related guides
- What happens on installation dayInstallers fix the indoor and outdoor units, link them with insulated pipes through a hole in the wall, test the pipework for leaks and clear it of air, then connect the power, run the system and show you how to use it.
- What a service involvesA service is a clean and check of the whole system, indoors and out, plus tests of how it runs and a look for leaks and wear. Manufacturers typically recommend one regularly, often once a year.
- The modes explained: cool, heat, dry, fan and autoCool lowers the temperature and takes out some moisture, heat warms the room, dry mainly removes moisture with gentle cooling, fan only moves air, and auto chooses between cooling and heating for you.
- How to clean the filtersSwitch the unit off, lift the front panel and take out the mesh filters, then vacuum or rinse them in lukewarm water and let them dry fully before refitting. In regular use, this usually needs doing every few weeks.