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Guide to Heating System Low Water Cutoff Safety Switches - LWCOs
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Here we discuss Low Water Cutoff Controls: Guide to LWCOs on hot water heating systems and we provide a low water cutoff switch Troubleshooting & Repair Guide. Readers will also find that this website answers most questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

A Guide to Inspecting and Flushing Low Water Cutoff Valves on Steam Heating Boilers

Low Water Cutoff - LWCO's on heating boilers: this steam heating boiler safety device contains a sensor, installed on many modern residential hydronic heating boilers and on virtually all steam boilers, is also installed on all commercial boilers of both types. The low water cutoff is a device intended to to turn off electrical power to the oil burner should the water level or pressure in the system fall below a safe level.

Sediment and Low Water Cutoff Valves - Flushing Needed

In the photo at page top you can see that the owner has left a 5-gallon plastic bucket below the low water cutoff drain pipe. Since steam heating systems are constantly using water, losing some of it as water vapor venting at steam radiators, and regaining water as the automatic (or on some systems manual) water feeder replaces water in the system, these systems tend to produce sediment at the boiler.

If sediment collects in the low water cutoff valve it could prevent the valve's internal float from falling as water level in the steam boiler drops, thus preventing the valve from safely shutting down the boiler should water level fall to an unsafe level. For this reason the low water cutoff valve needs to be flushed regularly, often once a week.

When we flush a low water cutoff valve we open and shut the valve several times, opening it briefly - just a few seconds, then closing it each time. This avoids a large surge of cold water entering (and possibly damaging) a hot steam boiler, and it also seems to help stir up and remove sediment from within the low water cutoff valve.

After flushing the LWCO valve several times, when we see that clear water is coming out, the job has been done. Usually the total volume of water flushed is 2-4 gallons.

Be careful, when a steam boiler has been running, water coming out of the low water cutoff flush valve is hot and can scald a bystander.

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• Weil McLain Model GV Gas Boiler/gas valve CPSC recall/repair
• Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
• National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
• The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
• Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
• The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
• Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
• "Residential Steam Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
• "Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
• "Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
• Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
• Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
• Installation Guide for Residential Hydronic Heating Systems
• Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
• The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)

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