Why Do Solenoid Valves Get Hot? Causes, Problems & Solutions
Solenoid valves are widely used to control the flow of liquids and gases in industrial, commercial, and domestic systems. One of the most common questions is why solenoid valve coils become warm – or even hot – during operation.
In many cases this is completely normal, as electrical energy passing through the coil naturally generates heat. However, excessive temperatures can indicate electrical issues, unsuitable operating conditions, incorrect voltage, or mechanical valve problems.
Understanding why solenoid valves get hot helps improve reliability, reduce energy consumption, extend coil life, and prevent unnecessary failures.
How a Solenoid Valve Works
A solenoid valve uses an electrical coil to generate a magnetic field. When energised, the magnetic force lifts or lowers an internal plunger which opens or closes the valve.
As current flows through the copper winding inside the coil, electrical resistance creates heat. This heat is a normal part of solenoid valve operation.
The longer the coil remains energised, the more heat can build up.
Why Solenoid Valve Coils Generate Heat
Electrical Resistance Heating
Solenoid coils contain tightly wound copper wire encapsulated within insulation materials. As electrical current flows through the winding, resistance converts electrical energy into heat.
This effect is similar to a traditional filament light bulb or electric heater element.
Typical causes of normal coil heating include:
→ Continuous energisation
→ High ambient temperatures
→ AC magnetic losses
→ Restricted ventilation
→ Enclosed control cabinets
AC Solenoid Coil Inrush Current
Many AC solenoid coils draw a higher “inrush current” when first energised.
This higher current is required to move the plunger into position. Once fully energised, current consumption reduces to a lower holding current.
If the plunger cannot fully travel due to dirt, limescale, debris, wear, or incorrect pressure conditions, the coil may continue drawing excessive current and become unusually hot.
Continuous Duty Cycle Operation
Continuous duty coils are designed to remain energised for long periods. Even so, they will often feel hot to the touch during normal operation.
Intermittent duty coils are not designed for constant energisation and may overheat rapidly if used incorrectly.
Common Problems Caused by Hot Solenoid Coils
Reduced Coil Life
Excessive heat accelerates insulation ageing and internal winding degradation.
Possible symptoms include:
→ Premature coil failure
→ Reduced magnetic performance
→ Intermittent operation
→ Burnt insulation smell
→ Internal short circuits
Increased Heat Inside Panels & Enclosures
Multiple continuously energised coils inside cabinets or machinery can significantly raise internal temperatures.
This may affect:
→ PLC systems
→ Sensors
→ Power supplies
→ Electronic controls
→ Wiring insulation
Limescale Build-Up In Hard Water Areas
High coil temperatures can increase limescale formation in water valves, especially in hard water regions.
This can lead to:
→ Reduced flow
→ Internal sticking
→ Valve failure
→ Increased maintenance
This is especially common on:
→ WRAS approved valves
→ Coffee machines
→ Steam systems
→ Hot water systems
→ RO and filtration equipment
Higher Energy Consumption
Traditional continuously energised coils consume full holding power continuously, even after the valve has operated.
This results in:
→ Unnecessary energy usage
→ Excess heat generation
→ Higher running costs
How Hot Is Normal For a Solenoid Coil?
Most solenoid coils commonly operate between 50°C and 90°C depending on:
→ Coil design
→ Voltage type
→ Ambient temperature
→ Duty cycle
→ Ventilation conditions
A coil surface temperature that feels too hot to touch briefly may still be operating within manufacturer design limits.
Some insulation classes permit temperatures exceeding 100°C.
However, investigation is recommended if:
→ The coil smells burnt
→ Plastic housings discolour
→ The valve buzzes excessively
→ The coil trips protection devices
→ Operation becomes intermittent
Factors That Increase Solenoid Coil Temperature
Incorrect Voltage Supply
Incorrect voltage is one of the most common causes of overheating.
Examples include:
→ 50Hz coil operated on 60Hz supply
→ Over-voltage conditions
→ Under-voltage causing increased current draw
→ Incorrect AC/DC supply type
Poor Ventilation
Restricted airflow prevents heat dissipation.
This is common in:
→ Compact machinery
→ Enclosed cabinets
→ Outdoor weatherproof boxes
→ High ambient temperature areas
Mechanical Valve Problems
If the valve plunger cannot move correctly, the coil may remain under excessive load.
Common causes include:
→ Dirt or debris
→ Scale build-up
→ Worn components
→ Incorrect pressure differential
→ Damaged seals
Solution – PWM Energy Saving DIN 43650A Connector (24vDC)
PWM (Pulse Width Modulation) energy saving connectors significantly reduce solenoid coil temperatures after valve actuation.
After initial energisation, the PWM unit automatically reduces holding power while maintaining reliable valve operation.
Benefits include:
→ Dramatically reduced coil temperatures
→ Lower energy consumption
→ Reduced power costs
→ Extended coil lifespan
→ Reduced limescale formation
→ Lower enclosure temperatures
→ Improved reliability in confined spaces
These systems are especially beneficial for continuously energised valves and hard water applications.
Real-World Coil Temperature Reduction
During testing, standard continuously energised coils reached temperatures approaching +90°C after extended operation.
Using PWM energy-saving connectors reduced coil temperatures up to dramatically while maintaining reliable operation.
Typical results included:
| Connector Setting | Coil Temperature After 30 Minutes | Result |
|---|---|---|
| PWM DIN Connector – 80% Reduction | 24.3°C | Very low temperature rise |
| PWM DIN Connector – 65% Reduction | 31.4°C | Low operating temperature |
| PWM DIN Connector – 50% Reduction | 40.0°C | Controlled heat build-up |
| PWM DIN Connector – 35% Reduction | 51.2°C | Reduced coil temperature |
| Standard DIN Connector | 84.6°C | High coil temperature |
Results vary depending on coil design, ambient conditions, and valve type.
Typical Applications
PWM energy saving connectors are commonly used on:
→ WRAS approved water valves
→ Industrial process systems
→ Coffee machines
→ RO filtration systems
→ Steam equipment
→ Compressed air systems
→ Irrigation controls
→ Vending machines
→ Control panels & enclosures
Tips To Reduce Solenoid Coil Heating
→ Verify correct voltage and frequency
→ Ensure adequate ventilation
→ Avoid enclosed unventilated spaces
→ Maintain clean valve internals
→ Use correctly sized valves
→ Check pressure differential requirements
→ Consider PWM energy-saving connectors
→ Use low power or latching valves where appropriate
Frequently Asked Questions
Is it normal for a solenoid valve to get hot?
Yes. Most solenoid coils generate heat during normal operation due to electrical resistance within the winding.
Why do AC solenoid coils run hotter?
AC coils often generate additional heat due to inrush current and magnetic losses during operation.
Can excessive heat damage a solenoid valve?
Yes. Excessive heat can shorten coil lifespan, damage insulation, increase limescale formation, and reduce reliability.
How can I reduce solenoid coil temperature?
Using PWM energy saving connectors, improving ventilation, checking voltage supply, and maintaining the valve properly can significantly reduce temperatures.
Do PWM connectors save energy?
Yes. PWM connectors reduce holding power consumption after actuation, lowering both energy usage and heat generation.
PWM 20% Duty Cycle , does it need a cooling off period?
It mentions duty cycle. In a lot of applications, the coil will be powered on for long periods, maybe even 24hrs. We will be using the NASS 113-030-0028 24vDC Power 4 13/30 coil 15Watt IP65 final temp rise 95K. Possible or would the connector need a cooling period?.
As long as the ambient temperature does not rise too high, the product will be usable. On lower duty cycle the product has more time to "cool down," so a 20% duty is the best choice.
In my opinion, our product is usable, but the external temperature limits specified in the data sheets must not be exceeded.
By this, I mean the temperature around the product; that is, if it is installed somewhere, the devices in its vicinity must not cause the temperature to rise above the maximum temperature specified in the data sheet.
Summary
Solenoid valve coils become hot because electrical current flowing through the winding naturally generates heat. In many applications this is normal and expected.
However, excessive temperatures may indicate incorrect voltage, mechanical valve issues, unsuitable duty cycle operation, or restricted ventilation.
Modern PWM energy saving connectors provide an effective solution by reducing both power consumption and coil temperature while maintaining reliable valve operation.
When to Take Action
Some warmth is completely normal, but you should investigate if:
The coil surface is too hot to touch for more than a few seconds.
The plastic housing shows signs of melting, cracking, or discolouration.
This is picture of a burnt out solenoid coil 240v 50Hz coil.
AC (Alternating Current) solenoids have an inrush and holding current.
In this instance the INRUSH 17.6VA, HOLD 15.9VA (VA = Volts Amperes), so 230v with 17.6VA = 0.0765 amp.
The inrush current is higher than the holding current when it is lifting or moving an internal plunger.
When the plunger reaches the fully energised position the coil reduces power consumption to the holding current.
But, if the valve has debris preventing the plunger reaching its fully energised position the coil will continue to draw the increase inrush current - thus over heating.
The valve fails to operate reliably (sticking, buzzing, or weak opening).
In these cases, switch off the power and check electrical ratings, coil type, and valve condition.
View Heat Reducing DIN Connectors