The project came about following an order from the Vatican in the 1980s which stated that Roman Catholic places of worship should be reordered to be more like the way they were originally built.
Leaders at the religious site at Bellmont are also taking the opportunity to invest in new equipment, such as high tech low energy lighting that can be controlled via an electronic tablet.
Richard Keddie, the Cathedral's development officer, said: "We are having major works done to upgrade lighting and heating. This phase is expected to take until May this year to complete."
A preliminary phase of this work at the cathedral, which was designed by famous architect Edward Welby Pugin are taking place before work starts in earnest.
It is currently closed during weekdays to allow the work to be carried out. But it opens at the weekend for Mass on Saturdays and Sundays. cathedral authorities have apologised for any inconvenience caused.
Mr Keddie said the cathedral's popular Orchard cafe is remaining open throughout the period for all the social and charity groups that meet there.
He said the overall aim of the project is to take back the cathedral both visually and decoratively to the way it was built. That means removing whitewashing. In the process some of the cathedral's historic architecture has been revealed one more to the public gaze.
The work being carried out on the lighting and heating systems have been designed to reduce energy costs.
"It will be high tech, using a tablet to control it, making the system more energy efficient and sustainable," said Mr Keddie. ""It will also future-proof the cathedral."
Previous work on restoring the cathedral revealed a spectacular gothic tiled floor created by the famous architect Edward Welby Pugin. The tiles, from the late Victorian period and turn of the century, were buried beneath a suspended wooden floor.
At the time Mr Keddie said: “The project is about rediscovering beauty. The reordering has been spearheaded by a dedicated team here at the cathedral, who, under the guidance of Bishop Mark Davies, has worked with various heritage and church bodies to deliver a sustainable and future-proofing project.
“Being a once in a lifetime opportunity, the cathedral, a place of immense historical and religious importance, will certainly add value to our local and regional communities as well as offering enhanced pastoral outreach.”
A wrought iron cross has also been restored, repainted and returned to the cathedral’s roof, while the bell has also been restored, repaired and cleaned.