BRUSSELS—Euro zone finance ministers will start a discussion on Monday on how to change the often-broken EU fiscal rules so that governments actually observe them, a euro zone official said. The European Union’s Stability and Growth Pact is meant to stop governments from borrowing too much in order to safeguard the value of the euro common currency. But the rules have often been disregarded, leading in part to the 2010 sovereign debt crisis, with little attempt made to enforce them by applying financial penalties. “The discussion is starting from the realisation that sanctions have not seen that much use. No use, to be precise,” the senior euro zone official said. To appease financial markets as the debt crisis peaked, euro zone countries agreed in 2011 to make financial sanctions for running excessive deficits and debt more automatic and less subject to political discretion. They also introduced the possibility of fines …