It happened between 7.30pm and 8pm on Sunday, 21 March, when suspects entered Bairstows Mechanical Services in Dewsbury Road, Hunslet.
Three vehicles and thousands of pounds of stainless steel fittings were reported stolen.
Police have since recovered one of the vehicles – a Renault Trafic van. However, a Citroen Relay and Ford Transit van have not yet been found.
Officers are keen to speak to anyone who may have seen these vehicles being driven after 8pm on the 21 March, as well as anyone who may have more information about the fittings, which are prefabricated for waste to energy pipelines and would require a test certificate by anybody who purchased them.
Anyone with information which may assist this investigation is asked to contact Leeds District CID on 101