As described in typical safety guidelines, which condition triggers a low water cutoff?

• A. The circulator is a variable speed model
• B. The boiler input is less than 400,000 Btuh and the circulating system is below the lowest safe permissible water level
• C. The water is treated with demineralization
• D. The boiler input is greater than 600,000 Btuh

Answer: (D)