During the past 20 years, the fire protection of ancient churches in Sweden has been improved with the installation of fire detection, fire sprinkler and water mist systems. The project identified 52 churches with either traditional sprinkler or high-pressure water mist systems. The operating experiences of these systems were documented by interviews with the end users, fire protection inspectors, system installers and by study visits. Problems associated with the use of antifreeze for water mist systems were identified. Systems have experienced leakage, high system pressures during warm days and corresponding unintentional activations due to breakage of nozzles or nozzle glass bulbs. For both sprinkler and water mist systems designed as dry-pipe systems, unintentional activations have occurred during wintertime due to freezing. Testing of dry-pipe systems also revealed unacceptably long water delivery times and residual water in piping. Many of the smaller rural churches are using a high-pressure gas- (nitrogen) driven pump because the public grid is unreliable. Three suffocation incidents were documented when nitrogen was unintentionally released into the confined technical space. Two of the incidents can be described as profoundly serious. For traditional dry-pipe systems galvanized pipes are often used but cases of internal pipe corrosion and leakage from pipes were documented. The church facility managers have a key role in the daily supervision of these installations. But it requires effort, technical competence and not least a substantial deal of self-interest. For some churches, high staff turnover has contributed to a lack of competence and supervision and maintenance has been neglected. High frequency of fault alarms (operating alarms) was also perceived as a burden and is also costly. Overall, the occurrence of technical problems and excessive costs have contributed to the shutdown or even dismantling of water mist systems in ten documented cases.