Methods and apparatus are provided for detection of leaks in boilers (14) containing temperature control liquid which is supplemented with feedwater (36) and removed as blowdown (26), main steam and sootblower steam. In a preferred embodiment, the boiler has an automatic liquid level control mechanism. The methods include measuring rates associated with feedwater supplementation and removal rates, correcting the offsets between the supplementation and removal rates, determining the unaccounted for water rate, and comparing the unaccounted for water rate with zero to determine if a leak condition is present.