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#153539 01/08/04 09:02 PM
Joined: Jun 2003
Posts: 1,143
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Seems like an electric version of a 'thermocouple' - a heat/expanding aire pressure sensor to guarantee flame presence for a pilot fired gas burner. My dad changed over from oil fired to gas when we moved into our old house, and I remember having to swap them out every few years.

Nowdays, many control modules (Pilot? Why would I need to fly my boiler?) incorporate a "flame proof" (sensor), to ensure that there is, in fact, a burning flame, and not just a big cloud of gas vapors in your furnace/boiler. If the flame proof fails, it d/c's the power to the gas valve (solenoid), and shuts down the flow of gas. Usually, the chain of activity follows like this:

Thermostat calls for heat.
Pre-light gas flow (25% of "regular" flow for 5-10 secs)
Ignition fire (piezo for 5-10 secs)
Flame proof test-
Flame yes? then open valve rest of way.
Flame no? shut valve. Retry after 60-90 secs.
If burning, continue until thermostat is happy.

I assume that your Firematic operates in the same fashion.

I got to know the control module intimately due to a failure of mine one cold winter a few years back (!*#%^$( solid state (*&^#&!!!).

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#153540 01/09/04 04:08 AM
Joined: Jan 2003
Posts: 4,391
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iwire Offline OP
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Doug No the firematic makes sure there is no flame. [Linked Image]

It goes above the burner on the celling or sometimes right on the front of the boiler or furnace.

It is a single pole switch that opens when heated.

It is more like a high temp cut out, it kills all power to the boiler controls.

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts
#153541 01/09/04 05:02 PM
Joined: Dec 2003
Posts: 751
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Member
The High-limit pictured in this thread is not required by any code. NFPA 13, standard of installation for oil burners, recommends the installation of this device. I always install one anyway, though.


Earl
#153542 01/10/04 10:18 AM
Joined: Jun 2003
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Aaaah... sorry, missed that one.

I can understand a requirement for oil furnace (given poss. of spilled fuel), but for a NG/LP application?

Any gaseous fuel burning outside the furnace should burn off quickly. (Of course, if it's a broken pipe, shutting off the furnace won't really help much I suppose)

#153543 04/19/04 09:04 PM
Joined: Feb 2002
Posts: 840
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Member
Like Bob, I work in the states he mentioned (MA, RI)

I too don't understand why this would be required for a gas furnace, as the gas valve allready has a safety device built in. These devices aren't required above gas-fired water heaters or other gas fired appliances, so why would a furnace need one?

I have always installed them due to tradition but I won't anymore if I can find the applicable code references.

Also, the safety switch often installed at the top of the basement stairs or just outside the boiler room is another one that confuses me.

The firomatic requirement for an oil burner makes sense though, and is always done around here.

Peter


Peter
#153544 04/19/04 10:50 PM
Joined: Aug 2003
Posts: 1,374
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Moderator
Like I said before, I really don't know anything about these because it is a non-issue in my area. Here is something from the NFPA 54 (National Fuel Gas Code) handbook, however. (Bold added by me)

Quote
The following commentary was taken from the NFGC NFPA-54-2002 Handbook:

"The National Electrical Code requires a separate electrical circuit and over current protection for central heating equipment, as well as a means for disconnecting the power source at or within sight from the appliance. This separate circuit also can include circulating water pumps, valves, humidifiers, electronic air cleaners, and other accessories normally associated with the equipment. Certain appliances and installations also are permitted to be connected with a flexible cord that has a grounding-type attachment plug. The grounding-type attachment plug also serves as a disconnecting means for future service & maintenance. In subsection 8.6.4, note the phrase "a permanently live electrical circuit --that is, one that is not controlled by a light switch." This requirement thus prohibits "emergency shutoff" switches. In areas where oil is a common source of heating fuel, wall switches with red cover plates marked "Oil Burner Emergency Switch" are installed in buildings heated by fuel oil, as required by NFPA-31, Standard for the Installation of Oil-Burning Equipment, to stop the flow of oil to the burner. When converting an oil furnace or boiler to gas, the emergency switch must be removed. Emergency switches must not be installed when installing a new gas boiler. The emergency shutoff switch provides safety for oil-fired heating equipment, because failure of the boiler or furnace to shut off can prevent the oil pump from shutting off, thereby filling the equipment and surrounding area with oil. An oil pool fire is possibile. With gas-fuelded equipment, the emergency shutoff valve required in subsection 6.9.3 provides equivalent safety.


Ryan Jackson,
Salt Lake City
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