Heating Boiler Short Cycling Repair

POST a QUESTION or COMMENT about diagnosing problems with residential hot water heating systems: the heating boiler

Heating boiler short cycling off and on troubleshooting and repair.

Page top illustration: if the boilers temperature sensing probe is not properly installed, a result can be improper temperature sensing and boiler short cycling.

This article series explains how to recognize & diagnose problems with residential heating boilers, including loss of heat, heating boiler noises, leaks, odors, or smoke, and high heating costs.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

- Daniel Friedman, Publisher/Editor/Author - See WHO ARE WE?

Heating Boiler Short Cycling Causes & Cures

Here we list the causes and cures for hot water heating boilers or steam boilers that are cycling on and off too frequently or at unexpected intervals.

For forced warm air heating sytems that are short cycling see FURNACE FAN CYCLES DURING HEAT

If you don't know whether your heat is provided by a furnace (hot air) or boiler (hot water)

see HEATING SYSTEM TYPES

...

What Causes a Heating Boiler to Cycle On and Off too Often?

Boiler keeps cycling on and off

Our InspectApedia reader Norm asked:

We have a Slant Fin boiler that keeps kicking on and off.

We have replaced the control panel. had the pumps checked.

We don't know what else to do. do you have any suggestions? - On 2019-10-25 by Norm

Causes & Cures for Heating Boiler Short Cycling On and Off

Watch the boiler temperature; is it turning off because it's reaching the cutoff temperature (set on the primary control aquastat) ?

If so then yeah maybe a circulator pump isn't pumping or the system is air bound as you suggest.

But the problem can certainly be elsewhere.

You don't give the fuel (oil or gas) but often the problem with a boiler whose burner is short-cycling on and off is one of those that we list just below.

Air bound heating zones?

If a hot water heating zone is air-bound or partly air-bound, on a call for heat the boiler may quickly reach the aquastat HI LIMIT while heat has not yet satisfied the room thermostat, leading to boiler short cycling.

Repair procedures are at AIR-BOUND HEATING SYSTEMS
Aquastat settings: if you set the DIFF to the maximum of 25-30 F that will reduce boiler short cycling.

Details are at AQUASTAT HI LO DIFF SETTINGS and at BEST DIFF SETTING and at AQUASTAT TROUBLESHOOTING

Aquastat temperature sensor: An aquastat that is not working properly because it's not sensing boiler temperature consistently

See AQUASTAT SENSOR PROBE HEAT CONDUCTING COMPOUND

Bad primary control or flame sensor on oil fired boilers discussed at

RESET SWITCH, CAD CELL RELAY and at

STACK RELAY SWITCH
Boiler oversized: if the boiler is over-sized for the building's needs, a result is likely to be short on-cycles or more-frequent on-off cycles and less efficient, more costly boiler operation.

Combustion air deficiency

Watch out: this is an unsafe condition

See COMBUSTION AIR REQUIREMENTS
Chimney that's blocked

Watch out: this is an unsafe condition

Inspection tips that can help spot a chimney or flue at risk of being blocked are

at CHIMNEY INSPECTION INDOORS
Circulator Pump defects, circulator runs intermittently

See CIRCULATOR PUMP RUNS INTERMITTENTLY
Electric Boiler Short Cycling - improper control or delay settings
Gas burner short cycling and other furner and flame problems are explained

at GAS BURNER FLAME & NOISE DEFECTS
Oil burner short cycling:

are at OIL BURNER SHORT CYCLING

also see

Oil Burner Adjustment or Nozzle - boiler over-fired: Poorly-adjusted burner or improper oil burner nozzle that is firing at too high a rate (too high a GPH nozzle)

See OIL BURNER NOZZLE GUIDE
Steam boiler excessive water level or condensate return delay problems can cause boiler overfilling and lead to steam boiler sort cycling.

Repair details are at STEAM BOILER FLOODING / SURGING REPAIR
Thermostat Heat Anticipator Settings: while it would be unusual for a room thermostat to itself cause boiler short cycling, you can fine tune the boiler on-off cycle if your thermostat has a heat anticipator.

Details are at HEAT ANTICIPATOR OPERATION and at HEAT ANTICIPATOR vs SHORT CYCLING HEATER FAQ
Thermostat wires that are loose or shorted can also cause irregular burner operation.

See THERMOSTAT DIAGNOSTIC GUIDE
Zone Valve not Opening: on a call for heat the boiler may quickly reach the aquastat HI LIMIT while heat has not yet satisfied the room thermostat, leading to boiler short cycling.

See ZONE VALVES, HEATING

If your concern is for a heating furnace (forced warm air) short cycling, see FURNACE FAN CYCLES DURING HEAT

...

Research on Heating Boiler Short Cycling Causes & Cures

Argo AI-B ELECTRIC BOILERS for FORCED HOT WATER, IO MANUAL [PDF] (2004) Argo Technology, Inc., Berlin CT 06037, USA - Division of ECR International, PO Box 4729, Utica NY USA 13504-4729 Website: www.ecrinternational.com

Excerpt:

Adjustable time delays:

The parallel wired time delays allow optimumcontrol of the heating elements being energized. Certain electric boiler applications including elevated outside temperatures, small heating zones, radiant heat installations, and flow rates usually require maximum time energizing heating elements.

By increasing delay time in above cited applications, short cycling and excessive wear and tear on boiler components may be minimized, resulting in greater operating efficiencies and boiler reliability. - p. 8.
ATH Cast Iron Condensing Boilers Models KN-2 and KN-4 INSTALLATION & OPERATION MANUAL [PDF] KN-2/4-CM2-0714 42-9452 - Advanced Thermal Hydronics Co., (Mestek Co.) In United States: 260 North Elm St. • Westfield, Ma 01085 • (413) 564-5515 • Fax (413) 568-9613 In Canada: 7555 Tranmere Drive • Mississauga, Ont. L5s 1l4 • (905) 670-5888 • Fax (905) 670-5782

Include an adjustable "limit band" explained below, allowing the firing rate to be adjusted to avoid boiler short cycling.

Smith Boiler Co., SMITH 8 SERIES STEAM or HOT WATER BOILER-BURNER UNIT Installation& Operating Instructions [PDF] (2013), Smith Cast Iron Boilers, Westcast, Inc., 260 North Elm Street, Westfield, MA 01085 USA (413) 562-9631, FAX: (413) 562-3799 Website: www.smithboiler.com

Smith Cast Iron Boilers, 7555 Tranmere Drive, Mississauga Ontario L5S 1L4 Canada, Tel: 905 672-2883

Excerpt: The most commonly available reverse acting aquastat is a Honeywell L4006B. The aquastat should be mounted in an immersion well directly installed in the boiler.

The use of heat conductive grease, Honeywell part #972545, in the immersion well is strongly recommended for fast and accurate temperature response. Set this adjustable aquastat to make at no less than 130°F.

While this method can cause the circulator to cycle more frequently, setting the aquastat’s differential to the maximum 25-30°F will minimize short cycling.
McDonnell & Miller's HEATING BOILER BASIC OPERATION [PDF] McDonnell & Miller, retrieved 2019/11/06 original source: controlcomponents.com.au/Open-File/557/Boiler%20control%20basics.pdf

Excerpt: If the automatic water feeder adds water to the boiler (to maintain a safe minimum operating level), and then the condensate pump returns its water to the boiler, the boiler will most likely wind up with too much water. This excess water limits the boiler’s steam making space.

Without enough room to break free of the water, the steam can carry water up into the system piping. That leads to higher fuel bills, uneven heating, water hammer, scale formation in the boiler and burner short cycling.
LAARS Endurance EBP EDP EDN BOILER IO MANUAL [PDF] Document 1187D (2009) Laars Heating Systems Co. (A Subsidiary of Bradford White), 20 Industrial Way, Rochester, NH 03867 • 603.335.6300 • Fax 603.335.3355 1355 Kuehner Drive, Simi Valley, CA 93063 • 800.900.9276 • Fax 800.559.1583 (Sales, Service) 1869 Sismet Road, Mississauga, Ontario, Canada L4W 1W8 • 905.238.0100 • Fax 905.238.0105

Excerpts:

EDP/EDN boilers installed in radiant (in floor) systems and other low mass boilers should be provided with a buffer/blender tank to assure a controlled supply temperature, and to prevent short cycling. - P. 16

11.2 Short Cycling Possible causes

a. Reduced system flow - EDP

b. Thermostatic union (EDP) or anti-condensing valve not opening (EBP).

c. T-T wires cross connected (jumped) – improper installation - EBP or EDP/EDN

d. Leakage of flue products into the combustion air stream – Direct Vent Installations only, see Section 9.2.3, Resolving Lockouts. - P. 36

...

Continue reading at BOILER OPERATING PROBLEMS - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see BOILER OPERATING PROBLEM FAQs questions & answers about our list of boiler operating problems that help troubleshoot hot water or steam heat

Or see these

Suggested citation for this web page

SHORT CYCLING HEATING BOILER - on and off too frequently, at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING BOILERS

Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia

Ask a Question or Search InspectApedia

Share this article:

Questions & answers or comments about diagnosing problems with residential hot water heating systems: the heating boiler

Search the InspectApedia website

Need to make a private comment? Email editor@inspectApedia.com. We welcome email with your website content critique, corrections, suggestions or questions. Email is monitored daily but our workload may prevent an immediate reply. For immediate results, we hope you'll first try asking your question using the search box just above.

Citations & Reviewers

In addition to any citations in the article above, a full list is available on request.

R.E. Prescott Company, a producer of other REPCO™ residential and industrial products as well as a provider of design-build engineering services is at 10 Railroad Avenue, Exeter, NH 03833. Tel: 603-722-04321 or 888-786-7482. Trish O'Keefe from Prescott informed us (10/7/2009) that their company had nothing to do with the failed Repco heating boilers discussed at InspectAPedia.com.

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
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 #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.)
In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested

CONTINUE READING or RECOMMENDED ARTICLES.

Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: info@carsondunlop.com. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.

Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The HOME REFERENCE BOOK - the Encyclopedia of Homes and to use illustrations from The ILLUSTRATED HOME .

Carson Dunlop Associates provides extensive home inspection education and report writing material. In gratitude we provide links to tsome Carson Dunlop Associates products and services.

	HOME	ABOUT	ASK a QUESTION	CONTACT	CONTENT USE POLICY	DESCRIPTION	POLICIES	PRINT	PRIVACY
	© 2026 - 1985 Publisher InspectApedia.com - Daniel Friedman

InspectAPedia^®

FREE Encyclopedia of Building & Environmental Construction, Diagnosis, Maintenance & Repair

The accuracy & trustworthiness of every article or Q&A is researched by human experts. See WHO ARE WE?

Question? Just ask us!

Heating Boiler Short Cycling Repair

Heating Boiler Short Cycling Causes & Cures