McDonnell & Miller Low Water Cutoff Parts and Service
McDonnell & Miller controls and parts on the shelf at our Oceanside, California, shop. McKenna technicians troubleshoot, replace, and test them across California.
Code-built boilers and vessels
Code repairs and alterations
Factory-authorized Tech Center
Factory-authorized Burner Tech Center
Fifth generation, family-owned
Before you call
Low water cutoff tripped? Leave the burner off.
Don’t add feedwater to a hot boiler that ran low, and don’t keep resetting the cutoff. Call (323) 987-1816 before anyone tries to restart it.
QUICK ANSWER
McKenna Boiler Works, Inc. keeps McDonnell & Miller low water cutoff controls and replacement parts on the shelf at its shop in Oceanside, California. Parts can be picked up, shipped, or installed. McKenna technicians troubleshoot, replace, set up, and test these controls on McKenna boilers and other manufacturers’ boilers, serving Los Angeles and all of California. Where ASME CSD-1 applies, the controls are tested to it. Call (323) 987-1816 or email info@mckennaboiler.com with the series and model number to confirm the exact part.
How it works
What a low water cutoff does and why it fails.
A low water cutoff shuts off the burner when boiler water drops to the lowest safe level. Firing a boiler with low water overheats the tubes and furnace and can cause a pressure vessel failure.
McDonnell & Miller float controls use a float to sense level. The float sits in a chamber piped to the boiler, or directly in a boiler tapping. Many also start and stop the feed pump and sound a low water alarm. The 751P and 752P sense level electronically with a probe.
Most failures start in the chamber. Sediment and sludge in the float chamber and equalizing piping slow or hold the float, so the switch reads the wrong level. Skipped blowdowns make it worse, and switches wear with age.
A trip is often the control doing its job. Before anyone resets it, find out why the water dropped: the feed pump, the feed valve, the condensate return, or a leak.
Parts and service
What McKenna stocks and does.
- McDonnell & Miller replacement controls and parts on the shelf in Oceanside
- Replacement head mechanisms where the float chamber and piping are sound
- Troubleshooting of low water trips, feed pump problems, and nuisance alarms
- Float chambers and equalizing piping opened, inspected, and cleaned of sediment
- Controls set to the boiler manufacturer's lowest safe water level
- Testing of feed pump control, burner cutoff, alarm, and manual reset
- Primary and secondary cutoffs checked against ASME CSD-1 where it applies
- Pickup, shipping, or installation by McKenna technicians
Read these off the control before you call
Series and model
On the control body or its nameplate, for example 150S, 93, 67, or 751P. The letters matter: on Series 63, the M models are manual reset.
Part number
On the nameplate or the carton. A photo of the label is the fastest way to match it.
Reset type
Automatic or manual reset. A manual reset control has a button that must be pressed before the burner can fire again.
Pressure rating
The control’s maximum pressure, from the label.
Electrical
Voltage and switch ratings on the label.
Job on the boiler
Primary or secondary cutoff, and whether it also runs the feed pump or the alarm.
Mounting
A chamber with equalizing piping, or a control set directly in a boiler tapping, and the pipe sizes.
Boiler nameplate
Boiler make, model, serial number, and operating pressure.
McDonnell & Miller series McKenna works on
Ratings are McDonnell & Miller’s published figures. McDonnell & Miller is a Xylem brand. McKenna is an independent boiler company, not an authorized McDonnell & Miller distributor or service center.
Series 63
Mechanical float cutoff for steam and hot water boilers, to 50 psi. Manual reset model: 63-M.
Series 67 and 767
Float cutoff for steam boilers, to 20 psi. The 767 threads into a 2-1/2 in. boiler tapping.
Series 93, 193, 94, 194
Float controls, to 150 psi (93 and 193) and 250 psi (94 and 194). Replacement head mechanisms are available.
Series 150S and 157S
Float cutoff and pump controller for steam boilers, to 150 psi. Controls the feed pump, the burner, and a low water alarm.
Series 751P and 752P
Electronic probe cutoff. Primary or secondary on hot water boilers; secondary on steam boilers to 15 psi (manual reset models).
On the shelf
McDonnell & Miller replacement controls and parts. Call to confirm the exact part number.
Service area
Pickup at 2601 Industry Street, Oceanside, California, or shipped. Technicians serve Los Angeles and all of California.
How a job runs
How a low water cutoff job runs.
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