Lift company Sigma Elevator is still banned from tendering for new projects, said HDB, as its performance has yet to meet the required standards.
The update comes nearly a year after the Housing Board said it had forbidden Sigma from bidding for new projects since October 2015.
This is so that the firm - a subsidiary of American company Otis Elevator Company belonging to the United Technologies group - can "focus on improving the installed lifts under their current contract".
Noting "some observed improvements in the performance of these lifts", the HDB spokesman told The Straits Times: "We are closely monitoring the progress of the improvement works, and will review their status after they have fully met our lift performance and service standards."
There are around 3,500 lifts built by Sigma out of about 24,000 lifts in HDB estates here. In 2013, HDB awarded a tender to the company to install 469 lifts in new flats. But the company, unable to meet deadlines, was not allowed to tender for new projects in 2015.
Last year, HDB noticed a higher-than-usual breakdown rate in the lifts installed by Sigma in their first year of operation. An investigation found that the doors and sensors were more prone to misalignment, possibly due to knocks from rough usage because of renovation and home-moving activities.
This occurred mainly in lifts in their first year of operation, in newly completed flats under the 2013 tender. The company said it has worked closely with town councils and HDB to rectify the issues.
But there have been recurring problems with Sigma lifts that are not part of the 2013 tender as well. In five public estates tracked by ST - Punggol Arcadia, Edgefield Walk, Waterway Cascadia, Natura Loft and McNair Towers - Sigma lifts still break down repeatedly and are out of service for long periods.
Three of these - Punggol Arcadia, Edgefield Walk and Natura Loft - are about five to seven years old, and lifts there are not supplied under HDB's lift term contracts, but via each development's contractor.
In August, the Ministry of National Development revealed national lift breakdown figures for 2013/2014 and 2015/2016 in public housing estates, showing improvement. On average, there were 20 lift breakdowns per 1,000 lifts a month in 2015 and last year, down from around 30 in 2013 and 2014.
But not all residents have seen improvements.
At Punggol Arcadia, one resident, who started compiling an Excel document of "Lift Reports" from June, recorded a surge of nearly 50 lift incidents in September alone, up from 15 in the previous month. The last reported incident, said the resident, was on Nov 8. But his data did not say if each incident was a breakdown or a case of the lift being put out of service due to maintenance.
At Bishan's Natura Loft, the breakdown of high-speed Sigma lifts in the Design, Build and Sell Scheme estate's three 40-storey blocks has continued to inconvenience residents. On Aug 5, nine people were trapped in a Natura Loft lift for over an hour when it stopped between two levels. A Sigma technician arrived late as he was stuck in traffic, ST understands.
When oral exams for the Primary School Leaving Examination were held later in August, a Sigma technician was put on standby at the blocks to assuage parents' worries.