If your heating system won't turn on at all, first check the following things in this order:
Is the thermostat working at all - is it on?
Check that the thermostat has power: if your thermostat is a programmable model or has an LCD or electronic display and the display is blank (red arrow in our photos) then the thermostat has no power - its main power source is off and its backup batteries are dead..
On an older analog dial type thermostat you can't determine if the thermostat is working just by looking.
But turning the thermostat UP well above room temperature should turn the heating system on. Thermostats are usually powered by a low-voltage system wired from a transformer near or right on the heater.
If the thermostat has no power, check that its wires are connected, intact and that power is turned on at the heating system since power off there will often also turn off the transformer that powers the thermostat. Then
see LOW VOLTAGE TRANSFORMER TEST
Check that the Heating Thermostat is set to "HEAT (on)". If a room thermostat is in the OFF position or is set to a temperature that does not call for heating (or cooling) then the heating or cooling system is just not going to run.
For the room thermostat shown at above left, push the clear plastic switch to the right towards HEAT as far as it will go.
Check that the Heating Thermostat FAN switch is set to AUTO if the switch is present on your thermostat.
If your thermostat has a FAN control switch but your building only has hot water or steam heat, most likely this switch does absolutely nothing.
For forced warm air heating systems, AUTO will let the fan turn on and off when the heating furnace runs while ON forces the fan to stay on constantly.
See FAN AUTO ON THERMOSTAT SWITCH for details about what turns the blower fan on and off on forced warm air heating systems or on air conditioning systems.
Separately, a FAN LIMIT SWITCH, we describe how this additional control, located on the heating furnace itself, should turn the forced warm air heating blower on or off. Don't bother with that switch yet.
Check that the thermostat is not in "HOLD" or "Standby" mode.
If the set temperature is down lower than room temperature and the thermostat is in HOLD or STAND-BY mode (a feature present on most electronic thermostats) the device will not turn on heat until room temperature is below that HOLD number
until you return the thermo sat to normal or RUN mode.
In our photo my pencil is pointing to the "Hold" button and the red arrow shows that the display is telling me the thermostat is in HOLD mode.
Press the "Run" button (below my pencil point) to go back to normal operating mode for this thermostat - that is to get out of "HOLD" mode.
Check that that the set temperature is at least 5 degrees above the room temperature. Later you can set the temperature lower if needed. of how to set all types of room thermostats are
at THERMOSTATS, HEATING / COOLING.
Watch out: on some heating or cooling thermostats like the one shown at left, the device is so simple that the meaning of the temperature shown in the display may confuse you.
Left untouched and in HEAT mode, and controlling just a hot water heating boiler in this installation, the 67 degrees shown on the thermostat is the present room temperature.
So we cannot tell the SET temperature of this thermostat just by walking up and taking a look. So we don't know if the thermostat should be calling for heat or not, nor if it has been SET above the present room temperature.
Luckily and without even reading the instructions (a last resort for many of us) it's easy enough to figure out what's going on.,
The heating boiler was not running - I'd already checked that, and I'd also noticed that the radiators in the building were tepid or cool.
Just pressing either the "down" button (blue arrow pointing down in the photo above) or the "up" button (red arrow pointing up in both photos) will change the display to show me the present SET temperature.
Notice that the SET temperature is all the way down to 56 degrees? This thermostat has been told "don't turn on the heat until temperature in this room drops below 54F! No wonder the heat was not running. The room was already much warmer than that.
What if the thermostat doesn't turn on the heating (or cooling) system?
Now if I press the "up" button repeatedly until the SET temperature is well above 67F then the heat should turn on. It did.
If the thermostat does not cause the heating (or cooling) system to run when it should, there could be any of a number of problems (as we outline here) but among them you may need to check the thermostat itself or its wiring - starting
at THERMOSTATS, HEATING / COOLING.
Watch out: to avoid embarrassment, don't forget to check electrical power switches including service switches that someone may have set OFF. For example
see ELECTRICAL POWER SWITCH FOR HEAT
Check that the heating system is now running. If it is not, Check that electrical power to the heating system is turned on and for oil or LP gas check that there is fuel in the tank.
Just take a walk over to your boiler or furnace room and listen - you should hear the equipment running, and for oil or gas fired equipment the metal "stack pipe" (properly, the flue vent connector between the heater and the chimney) will be hot.
If none of these steps fixes the no-heat problem, depending on what kind of heat you have, see the explanation of no-heat troubleshooting in the articles listed below.
If you are confident that the no-heat problem is not due to electrical power having been turned off and not due to a thermostat not properly set, then you'll want to choose a no-heat diagnostic procedure depending on the type of heating system your building uses - listed just below.
Continue reading at one of the articles listed just below depending on the type of heating systerm your buildnig uses, or select a topic from the More Reading links or topic ARTICLE INDEX shown below.
No Heat from a Forced Hot Water Heating Boiler or Steam Heating Boiler
See NO HEAT - BOILER
Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
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 "The Nest Learning Thermostat", Nest Thermostat, 900 Hansen Way
Palo Alto, CA 94304, Tel: 855-4MY-NEST, Email: email@example.com, website http://www.nest.com/, retrieved 1/24/2013.
 Honeywell Controls, the company wants you to use their contact form at this web page: http://www51.honeywell.com/honeywell/contact-support/contact-us.html
Honeywell Consumer Products,
39 Old Ridgebury Road Danbury, CT 06810-5110 - (203) 830-7800
World Headquarters, Honeywell International Inc.,
101 Columbia Road,
Morristown, NJ 07962,
Phone: (973) 455-2000,
Fax: (973) 455-4807 1-800-328-5111
 White Rodgers Thermostats and HVAC controls,
Homeowner information: http://www.emersonclimate.com/en-US/brands/white_rodgers/Pages/wr-homeowner-info.aspx
Contractor information: http://www.emersonclimate.com/en-US/brands/white_rodgers/wr_contractor_info/Pages/white-rodgers-contractor-info.aspx
White Rodgers Product Catalog (don't misspell the company's name as White Rogers Thermostats) -
http://www.emersonclimate.com/Documents/thermostats.pdf - Thermostat Catalog
 Domestic Central Heating Wiring Systems and Controls, 2d Ed., Raymond Ward, Newnes, ISBN-10: 0750664363, ISBN-13: 978-0750664363, Quoting from Amazon.com:
This unique A-Z guide to central heating wiring systems provides a comprehensive reference manual for hundreds of items of heating and control equipment, making it an indispensable handbook for electricians and installers across the country. The book provides comprehensive coverage of wiring and technical specifications, and now includes increased coverage of combination boilers, recently developed control features and SEDBUK (Seasonal Efficiency of Domestic Boilers in the UK) boilers ratings, where known.
In addition to providing concise details of nearly 500 different boilers fuelled by electric, gas, oil and solid fuel, and over 400 programmers and time switches, this invaluable resource also features numerous easy-to-understand wiring diagrams with notes on all definitive systems. Brief component descriptions are provided, along with updated contact and website details for most major manufacturers.
 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 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.)
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.)
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. She wrote:
Our company manufactures & distributes residential water treatment equipment, including our Repco line of conditioners. We have a plumbing & heating supply dept as well. We are mistaken for the Repco Boiler company on a regular basis, most frequently in Oct. and Nov.
Any information you could give me on the other Repco company would be appreciated. We've assumed it is no longer in business, and we'd like to know that for sure. Many callers want to know where to get replacement parts and I would be glad to direct them if I knew...plus there's always a chance they might be interested in a Crown Boiler instead.
Thanks to Bottini Fuel service manager Ron Thomas for discussing aquastat functions, low limit controls, oil burner short cycling causes, and boiler maintenance, reliability, and service contracts 4/13/2010. Bottini Fuel is a residential and commercial heating oil distributor and oil heat service company in Wappingers Falls, NY and with offices in other New York locations. Bottini Fuel, 2785 W Main St,
Wappingers Falls NY, 12590-1576
(845) 297-5580 more contact information for Bottini Fuel
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.
"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,
Roger Hankey is principal of Hankey and Brown home inspectors, Eden Prairie, MN. Mr. Hankey is a past chairman of the ASHI Standards Committee. Mr. Hankey has served in other ASHI professional and leadership roles. Contact Roger Hankey at: 952 829-0044 - firstname.lastname@example.org. Mr. Hankey is a frequent contributor to InspectAPedia.com.
Arlene Puentes, an ASHI member and a licensed home inspector in Kingston, NY, and has served on ASHI national committees as well as HVASHI Chapter President. Ms. Puentes can be contacted at email@example.com
Wikipedia provided background information about some topics discussed at this website provided this citation is also found in the same article along with a " retrieved on" date. NOTE: because Wikipedia entries are fluid and can be amended in real time, we cite the retrieval date of Wikipedia citations and we do not assert that the information found there is necessarily authoritative.
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The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
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