Serious safety risk found in newest metro trains’ heating systems

A critical safety flaw in the heating systems of Helsinki’s newest metro trains has prompted urgent inspections and operational restrictions, Finnish public broadcaster Yle reports.

All 25 M300-series metro trains, manufactured by Spanish company CAF and introduced in 2016, are being examined after a malfunction caused overheating and smoke in a train at the Roihupelto depot in February. The fault, linked to auxiliary heating resistors, can trigger uncontrolled temperature rises, potentially leading to smoke or fire hazards.

Helsinki Regional Transport Authority (HSL) has ordered drivers to monitor cabin temperatures, ensuring they do not exceed 25°C. If temperatures rise, drivers must immediately contact maintenance staff. Trains may no longer be left unattended while powered on; if parked for extended periods, they must be fully shut down.

“There is no immediate fire risk, but unchecked overheating could produce smoke in the passenger area,” said Heidi Heikkilä, HSL’s rolling stock service manager. All faulty components have been replaced, and remaining parts from the same batch will be swapped as a precaution over the next two weeks.

Costs will be covered under the existing spare parts budget. The temporary operating restrictions are expected to lift by April 19, once all replacements are complete.

The M300 series, comprising 25 trains, was delivered in two batches—20 initially and five optional units later. The issue primarily affects the original fleet.