An apartment complex with 42 flats in Leiden was evacuated in the early hours of Monday morning after a carbon monoxide scare.
The fire brigade sounded the alarm after the residents in one flat were taken ill after breathing in the highly toxic but odorless gas.
Checks in other apartments revealed that more boilers were producing too much carbon monoxide, leading officials to evacuate the entire complex of over 100 people. All were allowed back home around 4am.
The gas in 10 homes where the boilers were not working properly was cut off before the families were allowed to return. Five people were taken to hospital for checks.
According to broadcaster NOS, the property is owned by a housing corporation but tenants were responsible for their own gas boiler maintenance.
Every year dozens of people are hospitalised in the Netherlands because of gas faulty boilers.
A year ago, three children were taken to hospital with carbon monoxide poisoning after lighting a barbecue to try to warm their cold house when the gas and electricity were cut off.