Should I repair or replace an ageing ducted system?

The decision usually turns on which component failed rather than on the system's age, because the cost of the parts differs by an order of magnitude.

Generally worth repairing

• Fan motors, capacitors, control boards and sensors. All are discrete parts with a bounded cost.
• Thermostats and zone motors.
• Refrigerant leaks where the leak can be found and repaired. Note that topping a system up without finding the leak is not a repair, and venting refrigerant is a regulated matter.

Generally points to replacement

• A failed compressor on a refrigerated system. It is the single most expensive component and on an older unit the economics rarely work.
• A cracked heat exchanger on a gas unit. This is a carbon monoxide risk and is not a repair. The unit should be shut down until it is dealt with.
• A system using a refrigerant that is being phased down, where future servicing will get harder and dearer.

The part people forget

Ductwork has its own lifespan. Flexible duct crushed, disconnected or degraded in a roof space will undermine a brand new unit, and it is invisible from inside the house. If you are quoting a replacement, get the ductwork inspected and quoted at the same time. Discovering it afterwards is the most common way a replacement disappoints.