I can not find the furnace in our home. Is it in the attic??? or crawl space??? i have a newer home in Phoenix

Hi Jan:
Really interesting............
A puzzle I've never encountered before.
I'm a retired Contractor and Building and Plumbing Inspector so can offer an answer based on experience.
- In hot weather, attics get REALLY hot.
- An attic is an unusual location for a hot water tank.
- A thermostat senses the temperature of the water in the tank and determines when it needs to be heated.
- I would be suspicious that in your installation, the temperature in your attic is higher than the "high limit" for your water heater.
To phrase it another way, since the attic temperature is really high, and the tank thermostat is in the attic, it "thinks" that the water is already at the required temperature.
The only real "fix" that I could suggest would be to locate the hot water tank in the moderated temperature area of the dwelling.
Hope this helps.
I would appreciate your letting me know by comment to this post if that is the problem.
Cheers, and thanks for the puzzle.

pilot lit on gas furnace, but the burners won't light (Home ...

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Oct 26, 2013 - i have a gas furnace with a lit pilot, but the burners won't light. ... if the thermocouple does not sense the heat of the pilot it prevents the gas controller fromturning on the burners. ... clamped onto the outgoing hot water pipe, if huydronic system) that is telling the furnace it is too hot, whether or not that is true.

Some thermostats allow you to change the differential value - that is how far below the heating (or above the cooling) set point before calling for heat (or cooling in the case of air conditioning). The built in 1 degree differential setting provides the most even temperature in the space at the expense of more frequent furnace firing and stopping. Many people prefer this mode as opposed to allowing wider swings in temperature for less frequent furnace firing and stopping. If you wish to change this setting, you'll need to replace the thermostat as it is not user adjustable in this model.

For clarity, a Furnace produces HOT AIR for heat while a boiler produces HOT WATER for heat. Just remember...boil = water. You said your "furnace" does not produce hot water for a shower and because furnaces do not product hot water unless they have some model that do???? Usually people with a furnace have a seperate hot water heater. People with boilers though can produce hot water for use as both their sinks/showers hot water and their heat (by heating water that goes through baseboards) in their house. I don't believe any furnaces produce hot water most of the time a furnace just produces hot air for heating. So figure out what you first have.
Having said that, I'll assume you have a boiler like I do and my Weil McClean(sp?) stopped working a while back and wasn't turning on to "boil" any water. I took apart the burner and there is a light sensing photo resistor as part of the controls. If this phto resistor goes bad, the boiler will not start. The resister is cheap, I think it was $8 but you have to know what you're doing to change it. So you may be better to call someone who can work on such equipment.
Boiler's themselves are not overly complex. Home heating oil is the same diesel fuel that you can buy in a gas station only the government has "oil" companies put a RED die in home heating fuel which is usually cheaper then Diesel fuel because diesel fuel is taxed to death. The reason they do that is so that if you try putting RED tinted home heating fuel in your truck and you get pulled over (because you're a trucker with and 18 wheeler and they typically do inspections of these trucks) you will be a huge fine if they see you're running home heating fuel and NOT paying your taxed by purchasing Diesel fuel. A little bit of background so you know the fuel you are dealing with here. So it's dieslel fuel without the tax you run in your boiler. Gasoline on the other hand is VERY explosive as you know, but diesel fuel (if you're ever tried to light it) takes some coaxing to get lit. When it's cold out, diesel fuel is very hard to light and that's why trucks use glow plugs. You don't need those in your home though.
But because diesel fuel/home heating oil is hard to light, it's sprayed as a msit into your boiler, so that it can light more easily.
But because it is a fuel, you should know what you're doing when messing with it. FInd out what you have, and then have someone work on the issue if you haven't already. I'm guessing you have had it fixed by now?

Probably bad news if steel tank is leaking.

1) Copy following link for do-it-yourself troubleshoot walk-thru:
http://waterheatertimer.org/Leaking-water-heater.html

2) Drain tank and set in a drip pan with drain line to outdoors.
http://waterheatertimer.org/images/Water-heater-drip-pan-2.jpg
http://waterheatertimer.org/Water-heater-will-not-drain.html

3) If tank ruptures, it will flood home

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

You have tank-type gas water heater:
Open following link to watch thermocouple replacement.
Make sure new thermocouple sits into pilot flame. Instructions for relighting water heater are usually printed on side of tank.
http://www.youtube.com/watch?v=v0aBPsNg6vo

Gas water heaters need working thermocouple, adequate incoming fresh combustion air with no trace amounts of chemical, open vent to outside that drafts poison combustion product upward, clean burner tubes and combustion parts, correct gas pressure with no air in line, working gas control valve thermostat, no lockout condition such as tripped ECO caused by runaway heating and dirty combustion parts, and no lockout condition such as exposure to flammable vapors.
Open following links for troubleshoot resources:
http://waterheatertimer.org/How-to-install-gas-water-heater.html#troubleshoot

http://waterheatertimer.org/pdf/Pilot-light-will-not-stay-lit.pdf
http://waterheatertimer.org/pdf/Attic-Ventilation-and-Pilot-Outage-in-Gas%20Water-Heaters.pdf

http://waterheatertimer.org/images/Water-heater-in-attic-800.jpg
http://waterheatertimer.org/images/Test-water-heater-vent-1400.jpg

Plumber is right.
Problem is not amount of air in attic. Problem is how hot the air is.
Oxygen molecules separate apart in very hot air and pilot light goes out since there is not enough oxygen density to support combustion.
http://waterheatertimer.org/images/Water-heater-in-attic-800.jpg
http://waterheatertimer.org/pdf/Attic-Ventilation-and-Pilot-Outage-in-Gas%20Water-Heaters.pdf

More ventilation is needed.
Plumber is not ventilating expert, and not responsible for attic ventilation that builder failed to install. Plumber should do a survey of location before installation to make sure gasoline vapors are not stored nearby, but summer attic ventilation is gray area until more general-public folks become aware of problem. Hotter summers temperatures will spread that information.

Hire local home center to install roof vents AND soffit vents.
Note: You also need soffit vents.
Remember a vent on the roof is like sucking air out of a coke bottle. The roof vent is no good unless air can also enter the attic from another vent located in the soffit.

Another solution is electric water heater for very hot locations.
Or install solar-assisted water heater.
http://www.hotwater.com/products/residential/cirrex_solar.html

General causes for pilot going out: downward draft of air from outdoors, back-venting of furnace into water heater vent, bad thermocouple, or burner parts need cleaning, or bad gas control valve, or air in gas line.
Water heater in attic: hot attic conditions stop natural flow of vent gas upward.
Open following link for troubleshoot resources and cleaning illustrations and instructions:
http://waterheatertimer.org/How-to-install-gas-water-heater.html#troubleshoot
http://waterheatertimer.org/pdf/Pilot-light-will-not-stay-lit.pdf
Check venting by lighting a match under the vent hood and see if smoke drafts immediately upward.

If it bother you open a wind a little bit for fresh air till morning. It is telling you to change the battery. Why is it in the attic? It should be on the floor you are sleeping on for best protection.

You are talking about a gas fired system I assume. So no, it's not a big deal. Code now states that you need to vent the gas furnace from the attic or a crawl space and not from the living space. They change this code back and forth all the time. It's nothing to worry about if you do not plan to sell the home.