The 50% rule
The standard benchmark used by commercial HVAC engineers for the repair-or-replace decision is straightforward: if the cost of repairing the fault exceeds 50% of the cost of replacing the unit with a new equivalent, replacement is usually the better investment.
The logic is simple. A repaired unit still has an aging compressor, aging electronics and aging pipework. A new unit comes with a full manufacturer warranty, modern efficiency ratings and a full expected lifespan. Spending £800 repairing a unit that would cost £1,500 to replace often makes sense. Spending £800 repairing a unit that would cost £1,200 to replace — on a 12-year-old system — rarely does.
- Unit is under 8 years old
- Repair cost is under 50% of replacement
- Only one fault — not a pattern of failures
- Compressor is not involved
- Unit has been regularly serviced
- Refrigerant type is still available
- Unit is over 10 years old
- Repair cost exceeds 50% of replacement
- Repeated faults in the past 12 months
- Compressor failure on an old unit
- Refrigerant type being phased out
- Running costs have risen significantly
Verdict by fault type
Not all faults are equal. A fan motor failure on a 4-year-old unit is a straightforward repair. A compressor failure on an 11-year-old unit is a different calculation entirely. Here is how our engineers approach the most common AC faults.
| Fault | Typical repair cost | Verdict | Notes |
|---|---|---|---|
| Capacitor failure | £80–£160 | Repair | Low-cost part, quick fix. Always repair regardless of unit age. |
| Fan motor replacement | £150–£280 | Repair | Standard repair on units under 12 years. Parts widely available. |
| PCB / control board | £180–£380 | Repair | Repair on units under 8 years. Assess on older units — proprietary boards can be expensive. |
| Refrigerant recharge | £150–£300 | Repair | Always fix the leak source first. Recharge alone without leak repair will fail again. |
| Sensor / thermostat | £90–£180 | Repair | Low cost, always worth repairing on any age unit. |
| Drainage / blockage | £60–£120 | Repair | Maintenance issue, not a system failure. Always repair. |
| Compressor failure — unit under 8 years | £500–£1,000 | Assess | Compare repair cost against replacement carefully. May be worth repairing if unit is young and otherwise sound. |
| Compressor failure — unit over 10 years | £500–£1,000+ | Replace | Compressor failure on an older unit usually means replacement is better value. Other components will follow. |
| Heat exchanger damage | £400–£800+ | Replace | High repair cost on a core component. Replacement is almost always better value. |
| Multiple concurrent faults | Varies | Replace | Multiple failures signal end-of-life. Fixing one will not prevent the next. |
Age and repair cost together
Unit age and repair cost must be considered together, not separately. A £300 repair on a 3-year-old unit is an obvious decision. The same £300 repair on a 13-year-old unit with a history of faults is less clear. This matrix covers the main combinations.
What replacement costs in London
Knowing the replacement cost is essential for applying the 50% rule. Bear Building Services provides a free site survey and a fixed-price quote before any work begins — but these are the typical ranges for the most common commercial AC systems in London.
Free site survey. Bear Building Services provides a no-obligation site assessment and fixed-price quote for both repair and replacement — so you can compare the actual figures before making a decision. Call 020 3002 6826 or request a callback.
The refrigerant phase-out factor
One consideration specific to older AC units is the phase-out of certain refrigerants under UK F-Gas Regulations. Units manufactured before 2015 often use R-22 or R-410A refrigerant — both of which are subject to ongoing phase-down under the UK's post-Brexit F-Gas framework.
If your unit uses a refrigerant that is becoming scarce or significantly more expensive, the cost calculation for repair changes. A refrigerant recharge that cost £150 two years ago may cost considerably more today — and will likely cost more again in future. This is a legitimate reason to accelerate a replacement decision on an older system.
Our engineers will identify your system's refrigerant type and advise on availability and cost trajectory as part of any assessment visit.
What an honest assessment looks like
Our engineers give the same advice regardless of which outcome is better for the size of the invoice. If repair is the right call, we say so and provide a fixed quote. If replacement is better value, we say that too — and provide a replacement quote alongside the repair quote so you can compare.
What our engineers will never do is recommend a high-cost repair on a unit that is near end-of-life just to generate a larger callout fee. The alternative — recommending unnecessary replacement to sell a new installation — is equally something we avoid.
The question our engineers ask is simple: if this were their own business equipment, what would they do? That is the answer they give.
Frequently asked questions
Should I repair or replace my commercial AC unit?
If the unit is under 8 years old and the repair cost is under 50% of replacement cost, repair is almost always better value. If the unit is over 10 years old, has had repeated faults, or the repair exceeds 50% of replacement cost, a new unit is usually the better long-term decision.
What is the 50% rule for AC repair vs replacement?
If the cost of repairing a fault exceeds 50% of the cost of replacing the unit with a new equivalent, replacement is usually the better investment. This accounts for the remaining useful life of the old unit versus the full lifespan and warranty of a new one.
How long does a commercial AC unit last?
A well-maintained commercial split system typically lasts 12–15 years. Units serviced annually last longer than those without maintenance. After 10 years, major component failures become more likely and replacement becomes increasingly cost-effective.
What faults are worth repairing on a commercial AC unit?
Capacitor faults, fan motor replacement, sensor and thermostat issues, PCB replacement on younger units, and refrigerant recharge after a minor leak are all typically worth repairing. Compressor failure on an older unit is usually the point at which replacement becomes more economical.
How much does commercial AC replacement cost in London?
A single split system replacement typically costs £1,200–£2,500 supplied and installed. Cassette units cost £1,800–£3,200. Multi-split systems vary significantly by configuration. Bear Building Services provides a free site survey and fixed-price quote before any work begins.
Is it worth repairing an AC unit that is over 10 years old?
For minor faults — a capacitor, sensor or drainage blockage — yes, even on older units. For major faults — compressor failure or heat exchanger damage — replacement is usually more economical on a unit over 10 years old, as further failures become increasingly likely.
Not sure whether to repair or replace?
Our engineers assess your unit, give you an honest verdict and provide both repair and replacement quotes so you can compare. No obligation.