Matangi trains are ''more susceptible'' to frost because of ''sophisticated'' software meant to protect them from severe electrical fluctuations.
TranzMetro manager Scott Brooks said delayed services this morning were caused by frost and ice on overhead lines, triggering delays of up to 35 minutes on the Johnsonville line and up to 50 minutes on the Hutt line.
The Wellington region awoke to frost this morning and Mr Brooks said ice or severe frost on overheard lines could cause electrical arcs, which result in a power surge to the pantograph - the device on an electric train that collects current from overhead lines to power trains.
Matangi trains, which were introduced last year, were experiencing ''bedding in" issues and were ''more susceptible'' to surging than TranzMetro's Ganz Mavag and English Electric trains.
The Matangi had ''more sophisticated software which protects the train from severe fluctuations in power by temporarily blocking power to the unit with an electrical trip", he said.
The trip mechanism means the train's software system has to be reset.
''We have Matangi operating all services on the Johnsonville line and a number of services on the Hutt line, and the time it takes to reset the Matangi software meant delays this morning were longer than they would usually be on a cold day.''
Matangi engineers are looking into the issues caused by the icy conditions today, with ''a view to making some software adjustments".
''It's a matter of balancing the need to minimise service disruption with the need to prevent any damage caused by the icy overhead wires.''
He said the Ganz Mavag trains on the Upper Hutt and Kapiti lines could be ''slow to power up on cold mornings'' but delays would not normally be as long as they were this morning.
No further delays were expected today, Mr Brooks said.
Ngaio commuter Eric Consolo said a TranzMetro staff member laughed at him when he complained about the late trains.
Mr Consolo, who was on a delayed 6.39am train from Ngaio, asked about the delays and if preventive measures could be put in place to ensure trains ran on time.
''If you're travelling on the Johnsonville track you should not expect your service to be on time. There is always issues,'' the staff member allegedly said.
''She was making me feel dumb for expecting trains to be on time.''
TranzMetro's is investigating Mr Consolo's complaint.
- The Dominion Post
Who do you think won Key v Cunliffe's second debate?Related story: Leaders debate reveals more even contest