Heating system electrical shutoff switch (C) Daniel FriedmanGuide to Heating & Cooling Electrical Power Switches

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Electrical power switches & emergency off switches for heating equipment:

This article describes the usual location and function of electrical switches that control power to all types of heating equipment.

We explain the purpose and use of heating system emergency "off" switches, where they are located, how they are used, and wiring requirements.

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A Guide to Finding & Using Electrical Power Switches to Turn On or Off Heaters for Furnaces & Boilers, Heat Pumps or Electric Furnaces or Air Conditioners

Oil burner shutoff fuse switch (C) Daniiel Friedman

If your building has lost heat, checking that the heating equipment is actually turned "on" at all of these switches is a first step in diagnosing the problem. This article series answers most questions about central heating system troubleshooting, inspection, diagnosis, and repairs.

We describe how to inspect, troubleshoot and repair heating and air conditioning systems to inform home owners, buyers, and home inspectors of common heating system defects.

Electrical power switches on heating and cooling systems: where will the power switches be located, how do we know if we have turned on power to the heating or cooling system?

Our page top photo shows a typical emergency off switch for a heating system. Our photo at left shows a fuse box that is used to accomplish the same purpose, though this older switch is more likely to be found near the entry to a basement where heating equipment is located.

Electrical switches that turn off electric power that operates any type of heating system: furnace, boiler, steam boiler, heat pump, electric heat, are required for both safety and for service.

An emergency off switch for the building heating system should be found outside of the basement or other boiler or furnace room location and accessible so that an occupant can, in an emergency, turn off heat without having to enter a possibly smoky or dangerous area.

A second electrical "off" service switch should be found on or very close to the heating equipment itself. This second service switch is used by the heating service technician.

A third electrical switch or fuse turns off power to the heating equipment service at the building electrical panel. If a circuit breaker has tripped or a fuse has blown on the heating equipment's electrical circuit, you may be able to restore heat at the electrical panel.

But for safety reasons it is important to determine why the fuse blew or the circuit breaker tripped. If you replace a fuse or re-set a circuit breaker and the fuse blows or circuit breaker trips again, do not restore electrical power to that circuit - call a service technician to diagnose and repair the problem.

Questions & Answers about the emergency off switch on heating equipment

Question: My mom turns the boiler “service” red switch on and off all the time

My mom turns the boiler “service” red switch on and off all the time and I am worried that it is a danger. She has oil heat that primes a burner and I’m afraid that she is turning it off when the system is still on and demanding heat (programmed thermostat in other apt. units)and that this will create fumes, or some kind of buildup or off gassing.

There is no need for her to do this. She is elderly and is not thinking rationally. Can you advise please? Thank you in advance, Her daughter, K.E.

Reply: What sort of problems may be caused by frequent turning of the oil heat switch "on" and "off"?

Heat off switch (C) D Friedman

A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem or in this case that might indicate whether frequent "on-off" switching of the oil heater emergency off switch has caused an operating problem such as sooting-up of the combustion chamber or oil burner nozzle.

That said, here are some things to consider about using the emergency off switch on an oil fired heating system or oil fired water heater:

Infrequent (once a day or less often) turning on or off of an oil fired heating appliance (heating boiler or water heater, for example) at the service switch like the one you describe would not cause damage to the equipment though, of course, if someone leaves heat off in freezing weather a freeze-up in the building could lead to very costly damage.

Just turning off the oil burner, provided the system has reached full operating temperature, would not be expected to cause a problematic level of fumes or smells in the building.

Watch out: But frequent "on-off" switching of an oil fired appliance when it is in use (calling for heat or calling for hot water) could lead to a more subtle operating problem: it takes about five minutes for an oil fired heating appliance to reach full operating temperature.

Up until that time the system is not running as cleanly as it does at full temperature, it's a bit more smoky/sooty. So if someone keeps turning the system on and off frequently such that it does not sufficiently often reach full operating temperature, the result could be sooting and ultimately a clogged oil burner nozzle, leading to improper operation, inefficient operation, or even in the most extreme case, loss of heat.

Why don't you ask your mom why she's been turning the system on and off to see if you can find another way to ease her concerns.

Reader Comment: advice about oil burner emergency switches & their wiring

2 Feb 2015 NHFireBear said:

NFPA 31 for oil burners requires the "emergency switch" to interrupt the BURNER SUPPLY CIRCUIT, not the appliance power circuit. It is NOT the same as the "service switch" on the unit itself. The switch must be located outside of the room where the burner is installed.

There is no mention of cellar stairs, however, many fire chiefs and inspectors require the "emergency boiler switch" to be located on the upstairs side of the door to a cellar where an oil burner is installed. That way, not only does it allow you to shut off the burner without opening the door, it also signals the firefighters WHICH DOOR goes to the basement.

In a companion article at FIRE SAFETY CONTROLS NHFireBear also elaborated:

The "emergency" oil burner shutoff switch must be wired into the "burner supply circuit", according to NFPA 31. It is different from the "service switch" on the unit, which must be at or near the unit.

As mentioned in the FIRE SAFETY CONTROLS article [and in the article above on this page], the identified "emergency" switch must be located outside the boiler room and generally outside the door to the cellar steps, if the boiler is in the basement.

That way the switch can be turned off without opening the door, and the presence of the switch serves as a marker for which door is the one to the basement.

Many installers simply run the appliance power feed through the "emergency" switch, which means it ALSO turns off any sidewall vents, circulators, fans, thermostats, and other devices powered through the appliance controls -- not just the burner.

The NFPA is presently evaluating whether such an installation is safe, let alone proper, under the existing Code.


Thanks NHFireBear - we've added your note here and at FIRE SAFETY CONTROLS.

Really? Indeed it's an interesting point that if we shut off a blower fan on a furnace while the heat exchanger is still quite hot, the result could be a cracked (and thence unsafe) heat exchanger. On the other hand, if there is a building fire, particularly orignating in the furnace or boiler room, we hardly want to keep a furnace blower fan running.


How to Identify, Reset, or Adjust Heating or Air Conditioning System Controls and Switches

If you are looking for the main reset button on heating equipment you'll want to see COOLING & HEATING CONTROL & SWITCH INDEX - master index to all controls for cooling or heating equipment reset buttons, switches, controls, or see the suggested articles below:

The articles at this website describe the basic components of a home heating system, how to find the rated heating capacity of an heating system by examining various data tags and components, how to recognize common heating system operating or safety defects, and how to save money on home heating costs. We include product safety recall and other heating system hazards.


Continue reading at BOILER CONTROLS & SWITCHES or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see COOLING & HEATING CONTROL & SWITCH INDEX - index to all controls

Suggested citation for this web page

ELECTRICAL POWER SWITCH FOR HEAT at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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