An enforcement notice has been served on an incinerator by the Environment Agency (EA) after it found equipment not working on the site.
The EA discovered that equipment used to monitor total organic compound emissions from the Queen Street site in Leeds had not been working for three months.
White Rose Environmental who operate the incinerator had not picked up the fault in the equipment.
But measuring total organic compounds can be used as an indicator of whether the incinerator is working properly, although elevated emission levels would not cause any damage over the short to medium term according to the EA.
EA inspector George Marshall said: "It is a matter of principle that all equipment monitoring processes should be working at all times and wholly unacceptable that it took a routine inspection of ours to pick this problem up.
"We expect operators to take their responsibilities seriously and will be checking that the work we have specified is carried out by the end of June."