1. Introduction
This manual provides essential information for the proper installation, operation, and maintenance of your Marley Engineered Products Baseboard Heater Thermostat Temperature Control Knob. Please read these instructions carefully before use to ensure safe and efficient operation.
2. Product Overview
The Marley Engineered Products Temperature Control Knob is a replacement part designed for various baseboard heaters. It features a durable plastic construction with ribbed sides for improved grip and clear markings for temperature settings.
- Material: Plastic
- Outer Diameter: 2 inches
- Temperature Settings: Off, Lo, Med, Hi


3. Compatibility
This control knob is compatible with the following Marley Engineered Products baseboard heaters and accessory kits:
- Heater Series: 1800, 1900, 2500, 2600, C1800, and C2500 Series Model C baseboard heaters.
- Accessory Kits: TA1AW, TA2AW, TA1ANW, TA2ANW, TA1AWC, TA2AWC, TA1AWCA, TA2AWCA, TA1ANWCA, TA2ANWCA.
- Fahrenheat Models: FTA1A, and FTA2A baseboard heater accessory kits.
Note: This knob is designed for units with the knob mounted on the left front or right front of the heater. It will not fit units with the knob mounted on the ends.
4. Setup and Installation
Replacing your baseboard heater thermostat knob is a straightforward process. Ensure the heater's power supply is disconnected before proceeding with any installation or replacement.
- Power Disconnection: Turn off the power to the baseboard heater at the circuit breaker.
- Remove Old Knob: Gently pull the old knob directly off the thermostat shaft. It should slide off with moderate force.
- Align New Knob: Align the D-shaped opening on the back of the new control knob with the D-shaped shaft of the thermostat.
- Install New Knob: Push the new knob firmly onto the shaft until it is securely seated. Ensure it turns smoothly through all settings (Off, Lo, Med, Hi).
- Restore Power: Restore power to the baseboard heater at the circuit breaker.

Installation Video Guide
5. Operating Instructions
The control knob allows you to adjust the temperature output of your baseboard heater. Rotate the knob to select your desired heat setting:
- OFF: Turns the heater completely off.
- LO (Low): Provides a low heat output.
- MED (Medium): Provides a medium heat output.
- HI (High): Provides the maximum heat output.
Adjust the knob gradually to find the comfort level that suits your needs. The ribbed sides of the knob are designed for easy grip and smooth rotation.
6. Maintenance
The thermostat control knob requires minimal maintenance. To ensure its longevity and proper function:
- Cleaning: Wipe the knob with a soft, dry cloth to remove dust or dirt. Avoid using abrasive cleaners or solvents, as these can damage the plastic or fade the markings.
- Inspection: Periodically check the knob for any signs of wear, cracks, or damage. If the knob becomes loose or difficult to turn, inspect the thermostat shaft for issues.
7. Troubleshooting
If you encounter issues with your thermostat control knob, consider the following:
- Knob Does Not Turn Smoothly: Ensure the knob is correctly aligned and fully seated on the thermostat shaft. If resistance persists, check the thermostat mechanism for obstructions or damage (with power disconnected).
- Temperature Not Changing: If adjusting the knob does not affect the heater's output, the issue may lie with the thermostat unit itself rather than the knob. Consult a qualified electrician or the heater's manual for thermostat troubleshooting.
- Knob Falls Off: If the knob repeatedly falls off, the D-shaped opening may be worn, or the thermostat shaft may be damaged. A replacement knob may be necessary, or the thermostat shaft might need inspection.
8. Specifications
| Feature | Detail |
|---|---|
| Brand Name | Marley Engineered Products |
| Model Number | 42521-032-08 |
| Part Number | HU-XI-201 |
| UPC | 728433962565 |
| Material Type | Plastic |
| Item Weight | 8.98 g |
| Item Diameter | 2 Inches |
| Included Components | 1 Knob |
9. Warranty and Support
For specific warranty information or technical support regarding your Marley Engineered Products Baseboard Heater Thermostat Temperature Control Knob, please refer to the documentation provided with your baseboard heater or contact Marley Engineered Products directly through their official website or customer service channels.