A method for detecting a leak in a boiler having an automatic liquid level control mechanism in which a temperature control liquid in the boiler is supplemented with feedwater and is removed as blowdown comprising the steps of: a) measuring a rate of addition of a chemical tracer to said temperature control liquid in the boiler; b) measuring a rate that said blowdown is removed from the boiler, characterised in that the method further comprises: c) measuring a concentration of chemical tracer in said temperature control liquid in the boiler; d) measuring a rate of feedwater supplementation to the temperature control liquid in the boiler; e) determining the change in rate of said feedwater supplementation to the temperature control liquid in the boiler by taking the derivative of said feedwater supplementation with respect to time; f) determining the mass of said temperature control liquid in the boiler; g) determining the change of concentration of said chemical tracer in said temperature control liquid in the boiler by taking the derivative of said chemical tracer concentration with respect to time; h) determining the unaccounted for water rates using the following formula: LK = a * ChFd Ch - BD - b * d FW dt - M * d ln Ch dt Where: LK = unaccounted for water rate; a = a boiler dependent variable; b = a boiler dependent variable; t = time; ChFd = rate of addition of a chemical tracer to said temperature control liquid in the boiler; Ch = concentration of chemical tracer in said temperature control liquid in the boiler; BD = rate that said blowdown is removed from the boiler; FW = rate of feedwater supplementation to the temperature control liquid in the boiler; and M = mass of said temperature control liquid in the boiler; i) comparing said unaccounted for water rate with zero; and j) indicating a leak condition if said unaccounted for water rate is significantly greater than zero; wherein said rates are determined as weight per time unit. a) measuring a rate of addition of a chemical tracer to said temperature control liquid in the boiler; b) measuring a rate that said blowdown is removed from the boiler, characterised in that the method further comprises: c) measuring a concentration of chemical tracer in said temperature control liquid in the boiler; d) measuring a rate of feedwater supplementation to the temperature control liquid in the boiler; e) determining the change in rate of said feedwater supplementation to the temperature control liquid in the boiler by taking the derivative of said feedwater supplementation with respect to time; f) determining the mass of said temperature control liquid in the boiler; g) determining the change of concentration of said chemical tracer in said temperature control liquid in the boiler by taking the derivative of said chemical tracer concentration with respect to time; h) determining the unaccounted for water rates using the following formula: LK = a * ChFd Ch - BD - b * d FW dt - M * d ln Ch dt Where: LK = unaccounted for water rate; a = a boiler dependent variable; b = a boiler dependent variable; t = time; ChFd = rate of addition of a chemical tracer to said temperature control liquid in the boiler; Ch = concentration of chemical tracer in said temperature control liquid in the boiler; BD = rate that said blowdown is removed from the boiler; FW = rate of feedwater supplementation to the temperature control liquid in the boiler; and M = mass of said temperature control liquid in the boiler; LK = unaccounted for water rate; a = a boiler dependent variable; b = a boiler dependent variable; t = time; ChFd = rate of addition of a chemical tracer to said temperature control liquid in the boiler; Ch = concentration of chemical tracer in said temperature control liquid in the boiler; BD = rate that said blowdown is removed from the boiler; FW = rate of feedwater supplementation to the temperature control liquid in the boiler; and M = mass of said temperature control liquid in the boiler; i) comparing said unaccounted for water rate with zero; and j) indicating a leak condition if said unaccounted for water rate is significantly greater than zero; wherein said rates are determined as weight per time unit.