The owner of the Rugeley coal-fired power station has added another £25 million to the estimated cost of outages at the Staffordshire site.
International Power said the two units at the site were likely to be out of service until late September and early October respectively.
It has already estimated the financial impact of the extended outage at one of the units at £45 million. It added the second unit was likely to result in a financial hit of £25 million, but said the estimates were made before any recovery under Rugeley's insurance policy.
The site, which provides enough power for half a million homes, went offline for planned work in the first half of 2008, but on recommissioning one unit suffered a failure of a new component. The installation of flue gas desulphurisation equipment - part of efforts to ensure Rugeley complies with EU rules on sulphur emissions - will also be delayed from the third quarter of the year to early 2009 as a result.
Last week, IP said the second unit at Rugeley suffered a trip during recommissioning.
IP said: "Investigations to date indicate that both units at Rugeley have been impacted by a similar technical issue relating to the introduction of new equipment designed to improve the performance of the plant."
There are around 180 people employed at the site.