What is the maximum control voltage for a boiler?

• A. 120
• B. 180
• C. 150
• D. 240

Answer: (C)

Control voltage is the voltage that the boiler’s control devices (thermostats, gas valve relays, ignition modules) must tolerate. The controls are designed to operate safely only up to a certain voltage, because higher voltages increase the risk of insulation damage and arcing inside the control box. In typical boiler control hardware, the upper limit for control voltage is around 150 volts. Among common values, 150 volts represents that maximum capability, while voltages like 120 V are common but not the ceiling, and much higher voltages (180 or 240 V) would require different, specially rated equipment. So, the maximum control voltage for a boiler is 150 volts.