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Burners ignite, run high for 10 sec, then click and go to low, then repeat.

Burners ignite, run high for 10 sec, then click and go to low, then repeat.


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Old 11-22-10, 02:22 PM
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Burners ignite, run high for 10 sec, then click and go to low, then repeat.

I've got an old Thermo King. Trying to make it last. I noticed the hot air out of the registers wasn't all that hot. Went down to the basement, found that the furnace was going on, but the burners would ignite, run for maybe five or ten seconds, then a "click" was heard, and the burners would go low (not off). Then a few seconds at low, then they'd go up to high again. Then five or ten seconds later, a click, the burners go low, and it repeats, continuously. The house is warm enough, but there's obviously something wrong.
Hoping to get this fixed myself- I'm pretty handy. And I went thru an incident on another furnace where I thought it was the fuel valve, but thought I'd get an expert opinion. Called the local big HVAC company, and they sent a guy. He confirmed it was the fuel valve. I asked him for a quote. He looked it up, and said, "Around $600."
I stared at him, and said, "This is to install that valve, which I found available on line for under a hundred bucks?"
"That's it," he said.
"And am I right, that it's two 1/2" pipe connections, and two electrical connections to hook up? Taking about fifteen minutes?"
He looked uncomfortable. "That's what the book says. Sorry."
"Well, it was worth $60 to me, to have you confirm it's the valve."
"Yeah... you know to use pipe dope, right? Or teflon tape?"
"Yep," I said.
So I'm hoping to pick the collective wisdom here, and save some cash, toward a new furnace. Thanks!
 
  #2  
Old 11-22-10, 03:40 PM
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I recommend against replacing gas valves as a DIY job. There's more to it than you think. Do the job wrong or fail to do it completely and you can create a variety of safety problems.


Shop around. Look for someone who will charge you by the hour for repairs. Changing out a typical gas valve would take a skilled repairman a little less than an hour typically.
 
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Old 11-22-10, 04:36 PM
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Sorry, regarding the gas valve story- I was just going on about why I try to DIY when I can, to avoid horrendous overcharges. But it's good to know I could screw up, even when it seems simple!
No, my problem presently is this darn high/low burner problem. Any ideas?
(And FWIW, that gas valve I put in has been working for a couple of years, so I must have done it right.)
I should mention that the furnace is a natural gas burner, at least 20 years old. I'm outside Chicago, so we do get some cold weather. Not so far this year, though.
 
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Old 11-22-10, 08:21 PM
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I see now you made reference to "another furnace." Unfortunately errors in setting the burner input can cause excessive carbon monoxide, sooting, cracked heat exchangers or other problems.

You aren't really off the hook after two years.


What is the make and model of the gas valve on the furnace with which you are having problems?
 
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Old 11-23-10, 09:43 AM
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Sorry, I was hasty. The furnace is actually a ThermoPride, model IGH 13-125, 125,000 BTU, Cat. 1. The gas valve is a VR8440M. On closer observation, now the flames go off completely, the electric ignition makes the clicking noise, and the flames relight. They burn for about 5 seconds, go out completely, then the cycle repeats. So the house is warm enough for now, but I assume the furnace is running longer, since the flames are on for five seconds, off for two, on for five...
I tested the little diaphragm /microswitch that is hooked to the blower at the top of the furnace (it blows exhaust gases into the flue?) with a rubber tube- that works, according to my multimeter/continuity tester. And there's what appears to be a heat switch on the face, over the burners. When I shorted the terminals, it made no difference.
With the age of this furnace, I'm thinking it may be over the hill. But if it's just a simple part, I'd love to keep it going another couple of years if I can. Thanks in advance! Sorry for the sketchy info at first.
 
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Old 11-23-10, 10:15 AM
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Please describe the appearance of the pilot flame.

It should look like a small blowtorch with a solid blue flame that is relatively resistant to being blown around.

If it has a soft flame that is easily blown around or has yellow tips, the pilot burner and orifice need to be disassembled and cleaned. This can be the cause of the problem.
 
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Old 11-23-10, 10:32 AM
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Well, the pilot flame looks good and strong and blue. There's apparently a high voltage spark igniter (orange insulated wire) next to the pilot flame- that's what I hear clicking. The burners all catch fire nicely.
 
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Old 11-23-10, 11:33 AM
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You hyave an older Honeywell intermittent pilot ignition system. This doesn't have a high and low main burner flame arrangement ---when the main burner is switched on it should start at the high flame level and stay there.

I'd use an AC voltmeter to measure the voltages at the gas valve.

One 24 VAC circuit turns on the pilot burner gas and the other turns on the main burner gas. Check to see that you have the correct voltage.

Also, you need to check to see if you have the correct gas pressure. Do you have natural gas or propane? What other gas appliances do you have?
 
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Old 11-23-10, 12:11 PM
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Will do- thanks! We have natural gas. And I may have been wrong initially when I said it goes high and low- I might not have been looking closely enough. Now, it definitely is on/off.
We've got a gas stove. But nothing has changed, as far as new appliances or usage.
 
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Old 11-23-10, 01:25 PM
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The pilot gas and spark should turn on and the pilot burner light off the spark. Then the main burner should turn on and the main burner should light off the pilot light.

The main burner should stay lit until the thermostat is satisfied and shuts off.


That's what should happen. Careful observation of what is actually happening is important.
 
 

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