F-Gas Leak Checks: Intervals & Logbook Rules (UK)
How often must air-conditioning systems be leak-checked under GB F-Gas rules? The CO₂e thresholds, check intervals, logbook requirements and who can do them.
Last updated 15 July 2026
F-Gas leak checking is one of the clearest legal duties on an air-conditioning installer, and it's easy to get the interval wrong because it depends on the refrigerant charge expressed as CO₂ equivalent, not simply the weight in kilograms. This guide sets out the GB thresholds, how to work out which band a system falls in, and what you must record.
How the interval is decided
The mandatory leak-check frequency is set by the system's charge in tonnes of CO₂ equivalent (CO₂e). The higher the CO₂e, the more often it must be checked:
| System charge (CO₂e) | Minimum leak-check interval | With automatic leak detection |
|---|---|---|
| Below 5 tonnes | No mandatory check | — |
| 5 to 50 tonnes | Every 12 months | Every 24 months |
| 50 to 500 tonnes | Every 6 months | Every 12 months |
| 500 tonnes or more | Every 3 months | Every 6 months |
Systems of 500 t CO₂e or more must also have a permanent automatic leak-detection system fitted. Where a leak has been found and repaired, the system must be re-checked within one month to confirm the repair held.
Working out the CO₂e
The formula is simply the refrigerant charge multiplied by its Global Warming Potential (GWP):
CO₂e (tonnes) = charge in kg × GWP ÷ 1,000.
So a system holding 8 kg of R410A (GWP 2,088) is 8 × 2,088 ÷ 1,000 = 16.7 t CO₂e — in the 5–50 t band, so a 12-monthly check. The same 8 kg of R32 (GWP 675) is only 5.4 t CO₂e, just over the threshold. This is why the industry move to lower-GWP refrigerants pushes many smaller systems below the 5 t mandatory-check line.
Records and logbooks
For every system that requires checks you must keep records including the quantity and type of refrigerant installed, any added or recovered, the results of leak checks and the identity of the engineer/company. These records must be retained for at least five years and made available to the regulator on request. A site logbook kept with the equipment is the usual way to satisfy this.
Practical takeaways for installers
- Calculate CO₂e at design stage — it tells you the ongoing service obligation before you even fit the system.
- Lower-GWP refrigerants can move a system below the 5 t threshold, reducing the customer's compliance burden.
- Automatic leak detection halves the check frequency where it's worth fitting.
- Keep the logbook complete — missing records are the most common compliance failure.
Vento calculates CO₂e for each system automatically from the refrigerant type and charge, keeps the F-Gas register, and prompts the next leak-check date — so the compliance side looks after itself.
This guide is general information for UK installers, not legal or regulatory advice. Always check the current regulations and manufacturer instructions for your specific job.
Frequently asked questions
How often does air conditioning need an F-Gas leak check?
Under the GB F-Gas rules the interval depends on the charge measured in tonnes of CO₂ equivalent (CO₂e): systems of 5 to 50 t CO₂e are checked at least every 12 months, 50 to 500 t CO₂e at least every 6 months, and 500 t CO₂e or more at least every 3 months. Fitting a permanent automatic leak-detection system doubles the allowed interval, and systems below 5 t CO₂e have no mandatory check.
What is a tonne of CO₂ equivalent (CO₂e)?
CO₂e is the refrigerant charge (in kg) multiplied by the refrigerant's Global Warming Potential (GWP), divided by 1,000. For example 3 kg of R32 (GWP 675) is 3 × 675 ÷ 1,000 = 2.03 t CO₂e — below the 5 t threshold, so no mandatory leak check.
Who can carry out an F-Gas leak check?
Leak checking and refrigerant work must be done by an F-Gas certified engineer, working for an F-Gas certified company where required. Records must be kept for at least five years.
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