Methods and apparatus are provided for detection of leaks in boilers (10) containing a temperature control liquid (12) which is supplemented with feedwater and removed as blowdown. The methods include measuring rates associated with the feedwater supplementation and blowdown (18), adding a tracer to the temperature control liquid, determining the change in rate of the feedwater supplementation, determining the mass of the temperature control liquid, deriving the change in concentration of the chemical tracer in the temperature control liquid, calculating the unaccounted for water rate and comparing this rate with zero to determine if a leak condition is present.