Relays generally last around 200,000 cycles on average (roughly 18+ months depending on usage, firing temperature, and firing profile), but can fail long before or long after without any explanation.
Example
An 8-hour firing has 8 hours X 60 minutes X 60 seconds = 28,800 seconds. If your cycle time is set for 25 seconds then divide that by 25 = 1,152 relay cycles per firing. 200,000 divided by 1152 = 173 kiln firings.
