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#418184 - 11/30/07 09:17 PM Gas Furnace Pilot Issue
bubbadersh Offline
Super Handyman

Registered: 08/15/02
Posts: 2278
Loc: Southern California
I called the gas company in to do a routine safety inspection over the summer. One of the things the technician did was inspecting the furnace. At that time, he removed the cover over the burners and checked whatever he checks. I was watching and it seemed to me the pilot flame was much larger than what I expected to see. The tech said it was probably just he way it was back when the furnace was manufactured. I would very much appreciate your opinion. I took some pictures and movies (see below).

The unit is a forced air natural gas furnace (with standing Pilot) and with an A/C Evaporator on top. The house was built around 1966 and as far as I know this may be the original furnace and A/C unit. The information below is from the labels on the unit.

Gaffers & Sattler Corporation
Forced Air Furnace Model number: 125 FEF


Evaporator Model number: 50/60 TV H5


The Standing Pilot Valve Body says “Thermac Controls Company of America Gas Valve” 25V; 0.4A; 60cyc; NEC Class-2; ˝ PSI; G-LP; Part No. T-254




The furnace seems to be operating the same as it has for years. The thermostat controls and temperature regulation seems correct. The squirrel fan blower goes on and off at the expected times and sounds ok. All the connections I checked are not loose.

The pilot assembly in the picture below has three leads from the pilot valve body. I'm familiar with what the thermocouple in the middle does. I don't know why there seems to be a second gas line. Can you give me a quick tutorial on how the pilot works?



The lead on the left comes from a connection on the pilot valve body labeled “Pilot” with a screw next to it labeled “Pilot Adj.”. The lead in the middle comes from a connection on the pilot valve body and looks like a temperature thermocouple. The lead on the right comes from a connection on the pilot valve body labeled “Bleed” with a screw next to it labeled “Reg Adj.”.







Pictures of the pilot light flame:




And some movies:

1) Standing Pilot flame (99 sec video):


2) Burner flame (24 sec video):


3) Burner flame with cover on and blower running (21 sec video):


Waddaya think?

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#418185 - 12/01/07 09:31 AM Re: Gas Furnace Pilot Issue [Re: bubbadersh]
HeatPro Offline
Carpal Tunnel

Registered: 07/30/04
Posts: 28022
Loc: South New Jersey
You'll find a similar line to the 'bleed' on many commercial large gas regulators. As the seals aren't always 100% gas tight inside the case, a place for some gas to 'bleed' by the seals is sent to a safer place, on these older units, near the pilot to be burned off.

The pilot is allowed to burn too high, so the flame is impinging on the surface above to make a smoky fire. The pilot might be adjusted down under the cap next to the pilot where it is marked 'adj' with a small screwdriver.

The flame in the furnace is irregular in size from one burner to the other and there shouldn't be that large orange flame above it. A pressure adjustment can regulate that.

Seems either the tech hadn't a clue as to how to use a gas manometer, nor what a flame should look like, no cleaning experience, - or he was ordered just to inspect and try to sell a new one.

I am highly amused by the label that says the rise on the furnace is for 70 to 105F, which could mean return air of 70F could be heated to 175F to fry the dog or melt the plastic curtains next to the register. They are usually 50F rise today.
_________________________
Friends tell people how to live past 60.

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#418186 - 12/01/07 01:47 PM Re: Gas Furnace Pilot Issue [Re: HeatPro]
bubbadersh Offline
Super Handyman

Registered: 08/15/02
Posts: 2278
Loc: Southern California
Thank you for the feedback Harold. It sounds like I need to get some maintenance for this furnace.

The standing pilot flame needs to be adjusted downward. Would this be the screw labeled "PILOT ADJ."? Should I also clean the gas tube? I can see from the flame that there is gas coming out of the BLEED tube. Do you see that as a problem?

The burners need to be cleaned and the gas pressure adjusted downward. Would this be the screw labeled "REG ADJ"?

Do you know which way you turn the adjuster screw to lower the flame? I assume it has normal screw threads with in being clockwise and out being counterclockwise.

If it turns out the Thermac gas valve body is not working properly can I get it rebuilt or replaced easily? Can you tell from the information I've provided what the replacement unit would need to be?

Sorry about the barrage of questions but I'm trying to get a handle on this.

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#418187 - 12/01/07 03:55 PM Re: Gas Furnace Pilot Issue [Re: bubbadersh]
HeatPro Offline
Carpal Tunnel

Registered: 07/30/04
Posts: 28022
Loc: South New Jersey
Pilot adj screws are forms of machine screws, so turn the same directions; the screw turns less gas by closing off the port inside some more, so turning it clockwise would do that.

The flame size pressure adjust isn't a matter of turning the screw in alone. It will do that; but it is best to do that with a gas manometer in the manifold, so the pressure can be seen and written on the plate, so other servicemen can see that. This is also done while 'clocking' the meter to see what the input is and to compare it with the plate. Getting the flame too low can make a less efficient burn in the fixed chamber, which could show up in the fuel bill.

If the amount of gas coming out the bleed tube makes it difficult to adjust the flame to a blue lazy one, that is the sign the gas valve should be changed to a new one.

The old gas valves are replaced by the Honeywell Tradeline standing pilot gas valves at most plumbing/heating/AC suppliers. A new thermocouple and pilot would go along with that. The newer gas valves are safer than the old ones and don't need the bleed line.
_________________________
Friends tell people how to live past 60.

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#418188 - 12/01/07 07:12 PM Re: Gas Furnace Pilot Issue [Re: HeatPro]
bubbadersh Offline
Super Handyman

Registered: 08/15/02
Posts: 2278
Loc: Southern California
Both the "PILOT ADJ" and "REG ADJ" screws were already turned all the way clockwise. I guess this means it is time for a new standing pilot gas valve. Do you already have enough information so you could select a replacement? If you need more info just ask.

If you could give me a link(s) to a replacement gas valve you would choose and a replacement pilot and thermocouple I'd appreciate it very much. I'll probably end up calling an experienced tech to do the actual work but I'd like to further educate myself first and get a better sense of the costs involved.
_________________________
--- bub

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