A two-unit cold standby production system with one repairman is consid
ered. After inspection of a failed unit the repairman chooses either a
slow or a fast repair rate to carry out the corresponding amount of w
ork. At system breakdown the repairman has an additional opportunity t
o switch to the fast rate. If there are no fixed costs associated with
system breakdowns, then the policy which minimizes long-run average c
osts is shown to be a two-dimensional control limit rule. If fixed cos
ts are incurred every time the system breaks down, then the optimal po
licy is not necessarily of control limit type. This is illustrated by
a counterexample. Furthermore, we present several performance measures
for this maintenance system controlled by a two-dimensional control l
imit rule.