A fire broke out at the boiler house at Grantham Hospital last night (Sunday).
Six fire engines and a hydraulic platform were called to the scene in Manthorpe Road at around 7pm.
The flames were put out and the operation has been scaled down.
Fire services reported the blaze has caused fire, heat and smoke damage to the first floor workshop and there is fire damage to pipes and insulation on the ground, first, second, third and fourth floors.
There was also light fire damage to contents on the second floor.
The cause of the fire is believed to be an electrical fault on the first floor.
The hospital is currently accessing the damage and will release a statement today.
A spokesman for United Lincolnshire Hospitals NHS Trust, which runs the hospital, said: “There was no imminent danger to patients, staff or visitors at any time throughout the fire situation. During the fire parts of the site did not have cold water, but cold water was restored to the site by 11pm.
“The boiler is unfortunately now non-functional and therefore large parts of the site are without hot water.
“We are bringing portable boilers to the site and expect a normal hot water supply to resume from Wednesday at the latest. However, we have hot water to other parts of the hospital and are making arrangements for washing and bathing our in-patients.
“Apart from some disruption to some of today’s theatre cases we do not expect any further problems with all services working as normal from tomorrow (Tuesday).”