Software bugs that are blighting journeys on the Elizabeth Line will continue to affect services until they can be ironed out, Transport for London has warned.

The line’s core section between Abbey Wood and Paddington was closed over Easter to upgrade the software used in its signalling system to allow more trains to run at peak times.

From May 21, the line’s final timetable will be introduced, which will include rush-hour trains every five minutes from Woolwich and Abbey Wood.

But in the meantime passengers have recently suffered numerous delays and cancellations, with the whole central section – which includes Woolwich and Abbey Wood – grinding to a halt for part of last Tuesday.

Bugs in the system – known internally as EL400 – have been found, a report to TfL’s Elizabeth Line committee, which will meet next week, states. Siemens, which supplied the system, is releasing a number of patches to fix the issues.

“The performance affecting regressions in ELR400 will impact reliability until resolved in future patch releases,” the report warns.

TfL has also admitted to reliability issues with the Elizabeth Line trains, but says “a further train software upgrade to support this is being rolled out and will be fully loaded onto the fleet ahead of the 21 May 2023 timetable change”.

Issues with the line west of Paddington, which is controlled by Network Rail, are also reported. “There have been a significant number of points failures, which are disrupting and take time to recover the service,” the report says. The issues “continue to be a concern”, committee members have been told.

When the Elizabeth Line first came to Woolwich and Abbey Wood in May 2022, the service used only the “central section”, between Paddington and Abbey Wood, which is owned by Transport for London and uses state-of-the-art technology.

Since then it has been joined up to Network Rail lines to the east and west of London – as well as Heathrow’s own line to the airport – and engineers have faced a huge challenge in making sure different signalling systems can talk to each other.

One key aspect of Easter’s software upgrade has worked – trains that terminate at Paddington can now drive themselves into a siding before reversing back into the correct platform while the driver walks through the train to switch cabs. This will enable more trains – 24 per hour between Paddington and Whitechapel – to run at peak times.

A long-running pay dispute could close the line on its first anniversary, with the TSSA and Prospect unions planning to walk out on May 24. The unions say that many of their staff earn only two thirds of the salary paid to their counterparts elsewhere in TfL.

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