The smelter has been hit by an "unplanned stoppage".
The situation involving its new $660 million system has been described by former smelter worker and Independent Frome MP Geoff Brock as "teething problems".
The stoppage took place on May 28. Production is expected to resume at the end of this month.
Nyrstar said the blast furnace was shut down in May to allow the Top Submerged Lance Furnace or TSL to re-establish an adequate stock of product TSL slag feed for the furnace after an extended planned shutdown of the TSL in April.
"The blast furnace restart was unexpectedly delayed by a steam eruption in the refinery and a failed blast furnace water jacket. On June 5, a failure of the TSL main process gas duct, between the waste heat boiler and evaporative gas cooler, required another shutdown of the TSL for remedial work."
This requires a partial dig-out of the continuous drossing furnace, essential for treatment of all lead output from the blast furnace, as it has now solidified. The company's profit will suffer.