The coil is the electrical part that creates the magnetic field to move the solenoid valve mechanism. When a valve does not open, it is incorrect to immediately assume it is mechanically jammed. Often the cause lies in the supply voltage, the coil itself, or the control circuit.
How to identify the nominal voltage
The voltage is indicated on the nameplate or on the coil itself. It can be 24 V AC, 24 V DC, 110 V AC, 230 V AC or another value. We also check if a frequency of 50/60 Hz is indicated and if there is a special rectifier or electronic module.
What happens if lower voltage is applied
If the voltage is lower than the specified value, the magnetic field may not be sufficient to fully attract the armature. The valve may not open, may open slowly, or may produce a hum and vibration.
What happens if higher voltage is applied
Overvoltage can increase the current and the temperature of the coil, significantly reducing its service life. In case of a serious deviation, there is a risk of immediate destruction of the insulation.
Voltage measurement during the command
Proper measurement is not done only when the burner is on standby. The voltage must be checked when the automation system issues an actual opening command. This reveals if there is a voltage drop in relays, contacts, terminals, or wiring.
Coil testing without arbitrary powering
With the installation isolated according to the manufacturer's procedure, the technician can check the electrical continuity of the coil and compare the measurement with technical data. Very high resistance may indicate an open circuit, while an unusually low value may indicate insulation failure or a short circuit. Interpretation depends on the coil type, and there is no universal value for all valves.
Humming or intense vibration
In an AC coil, intense humming may occur when the moving core is not fully attracted, when there is dirt/wear in the mechanism, or when the voltage is low. Prolonged operation in this state can cause the temperature to rise significantly.
When the coil is hot but not necessarily faulty
Many continuous-duty coils heat up noticeably during normal operation. The temperature must be evaluated according to the manufacturer's limits and not just by touch. A burning smell, discoloration, melted plastic, or frequent fuse tripping are clearly more concerning signs.
The correct diagnostic sequence
We first confirm that the automation is requesting an opening, then we measure the actual voltage at the coil, and then we evaluate the coil and the valve mechanism. This avoids unnecessary replacement of a component when the problem lies in a preceding safety contact or the power supply.
Attention: Do not power a gas solenoid valve directly to bypass the burner's safety sequence.
