CSLB C-20 HVAC ContractorHeating SystemsMedium
A commercial hydronic boiler system experiences a sudden loss of water due to a leaking pipe fitting. Which safety device is designed to shut down the burner before the boiler operates with insufficient water level?
- AAir separator
- BPressure relief valve
- CAquastat high limit
- DLow water cutoff
Show answer & explanationAnswer & explanation
Correct answer: D. Low water cutoff
A low water cutoff (LWCO) senses water level in the boiler and automatically shuts off the burner if the level drops below a safe point, preventing dry-firing and heat exchanger damage or failure. This is a critical safety control required on most hydronic boilers by code.
Why the other options are wrong
- A. An air separator removes trapped air from the system but does not sense water level.
- B. A pressure relief valve protects against overpressure, not low water conditions.
- C. An aquastat controls water temperature setpoints, not water level.
Low Water Cutoff (LWCO)
A safety control on a hydronic boiler that senses water level and shuts off the burner if water drops below a safe operating level, preventing dry-fire damage.
- Required by code on most hot water and steam boilers
- Can be float-type or electronic probe-type
- Should be tested periodically per manufacturer instructions
Memory trick: No water, no fire — cutoff saves the boiler.