💧 142400 McDonnell & Miller #63 Low Water Cut-Off
For Steam or Hot Water Applications
The McDonnell & Miller 142400 (Model #63) Low Water Cut-Off is a mechanical float-type control designed to protect steam and hot water boilers from low water conditions. Engineered for reliability and long service life, this heavy-duty unit automatically shuts off the burner when water levels drop below a safe operating point — preventing costly damage and ensuring safe, efficient boiler operation.
✅ Key Features
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✅ For Steam & Hot Water Boilers – Ideal for residential, commercial, and industrial systems.
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✅ Automatic Reset – Restores operation once safe water level returns.
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✅ Float-Style Design – Proven mechanical reliability, no electronic sensing required.
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✅ Includes No. 2 Switch – Provides dependable pilot-duty control.
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✅ Heavy-Duty Construction – Built for continuous operation under demanding boiler conditions.
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✅ Optional Manual Reset Available – Enhances safety when required by local codes.
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✅ Compatible with TC-4 Testable Control – For hot water system use.
📊 Specifications
| Specification | Detail |
|---|
| Manufacturer |
McDonnell & Miller |
| Part Number |
142400 |
| Model |
63 |
| Type |
Mechanical Float Low Water Cut-Off |
| Application |
Steam & Hot Water Boilers |
| Reset Type |
Automatic |
| Switch Type |
No. 2 Switch |
| Maximum Pressure |
50 PSI (3.5 kg/cm²) |
| Electrical Ratings (AFL) |
10.2 A @ 120 VAC / 5.1 A @ 240 VAC |
| Electrical Ratings (ALR) |
61.2 A @ 120 VAC / 30.6 A @ 240 VAC |
| Pilot Duty |
125 VA |
| Frequency |
60 Hz |
| Mounting Type |
Boiler Side Mount |
| Optional Accessory |
TC-4 Testable Control (for hot water systems) |
⚠️ Common Symptoms When Replacement Is Needed
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Boiler cycles erratically or fails to fire
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Low water safety trips frequently without cause
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Visible corrosion or stuck float mechanism
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Electrical switch failure or burnt contacts
❓ FAQ
Q: Can this unit be used on both steam and hot water systems?
A: Yes — the #63 is designed for both applications and can be used with the TC-4 testable control on hot water systems.
Q: Does it include the switch assembly?
A: Yes, it comes with the No. 2 switch pre-installed.
Q: What is the difference between automatic and manual reset?
A: This model features an automatic reset, but a manual reset version is available for applications that require manual verification after low-water shutdown.
Q: What’s the maximum operating pressure?
A: The #63 is rated for 50 PSI (3.5 kg/cm²).
🛒 Shopping Tips
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Always verify your boiler’s operating pressure and voltage before ordering.
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For hot water systems, pair with McDonnell & Miller TC-4.
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Replace low water cut-offs during major boiler service or when performance issues occur.
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Use only genuine McDonnell & Miller parts for safety compliance and warranty protection.
