Trains used on a service between Hull and London are "not fit for purpose", an East Yorkshire MP has said.
Hull Trains is not running a direct service between Hull and London after a fire onboard a train caused disruption.
There has been extensive disruption to the timetable over the weekend after the fire at Grantham on Friday night.
Hull Trains said in a statement it was operating an emergency timetable after "a series of unrelated mechanical problems with our trains".
The timetable changes are due to last until Friday, the company said.
Emma Hardy, Labour MP for Hull West, said: "The trains are too old.
"I have some sympathy with Hull Trains but at the end of the day those trains are not fit for purpose."
Ms Hardy said the company had been "really successful for years" but was trying to run a profitable service with unreliable trains.
"They are patching up trains that are way past their sell-by-date," she added.
Louise Cheeseman, Hull Train's managing director, said the company's four trains were 18 years old and did 1,000 miles a day.
The trains were "getting a bit older and needed more TLC" and "unfortunately parts do fail on them", she added.
Hull Trains is to introduce a new fleet in 2019 but before then the company had to "focus on maintaining our trains", she said.
She said one train had a mechanical failure on Wednesday followed by Friday's fire when a train was halted at Grantham as smoke and flames were seen under a carriage.
Paul Rusling, who was on the train, said: "The lights went down and our crew went dashing off to the next coach, about five minutes later there is a kerfuffle and a shout 'Get out, get out" which chilled me a little because they were saying 'evacuate the train there's a fire'."
Currently dealing with a train on fire at #Grantham with @BTPNotts and @lincspolice. Fire crew are assessing the situation and luckily no injuries from passengers onboard. @FirstHTrains #ECML pic.twitter.com/1cRcOTptEd— BTP Cambridgeshire (@BTPCambs) October 5, 2018
Steve Montgomery, managing director of Hull Trains' parent company First Rail, said: "We're very sorry that our passengers on Hull Trains have experienced a reduced service following a series of unrelated mechanical problems."
He said additional engineering expertise was available and the company was "anticipating an improvement in service throughout the week, as our repaired trains come back into service".
Hull Trains told customers to check its website for journey details.
Figures from independent regulator the Office of Rail and Road show Hull Trains had the worst punctuality and cancellation record of all train operators over April to June.
A train also caught fire in May at Welwyn North.