A panel in fault is a building that is partly unprotected, so the first question is not what the repair costs but what is unprotected in the meantime and what you are doing about it. The repair decision comes second, and on older systems it is often a decision about whether the system has any life left rather than about one faulty device.
First, cover the gap
Establish from the panel which zone or device is affected and therefore which part of the building is not being watched. Until it is fixed, that area needs another way of raising the alarm: additional inspections, a temporary detector, or in the worst case not using the area. This interim arrangement belongs in the log book, because it is the evidence that the fault was managed rather than tolerated.
Repairs that are usually worth it
A failed detector on a system with spare capacity and available spares. A standby battery at the end of its life. A damaged cable run. A device knocked off during building work. All of these are ordinary maintenance on a healthy system and the fix is bounded and predictable, which is what makes them worth doing rather than deferring.
When replacement is the honest answer
Three signs. Spares for the panel are no longer made, so every future fault becomes a search. The system is a category below what the building now needs, so repairing it perfectly still leaves you non compliant. Or the fault log shows recurring problems in several zones, which usually means cable or environment rather than devices. At that point the repair spend is buying time on an asset you will replace anyway.
The spur, and why it matters
The panel takes a dedicated supply, often called the fire alarm spur, from a labelled protective device that nobody should switch off during other work. A surprising number of reported panel faults are somebody turning that off during unrelated electrical or building work. If your panel keeps losing mains, the first place to look is the board, not the panel.
Questions people ask about fire alarm repair
Can I reset a fire alarm panel to clear a fault?
Resetting clears the display, not the cause. If the fault returns it was never fixed, and if it does not return you still do not know what it was. Faults need diagnosing and recording.
How quickly must a fire alarm fault be fixed?
There is no statutory deadline, but the duty to maintain the system in efficient working order means a fault left standing needs an interim arrangement and a plan. Record both.
Is it worth repairing an old panel?
Only if spares exist and the system still meets the category the building needs. Where either is untrue, repair spending is deferring a replacement rather than avoiding one.