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h2ocoach 12-09-2012 07:31 AM

Furnance takes a very long time to light
 
I have a 20 year old carrier hot air furnace that takes a very long time to light but once it does it runs OK. I have an intermittent pilot with and electronic spark ignition. The ignitor will click for up to (the longest I timed) 8 minutes before the pilot light ignites and then ignites the burners. I have done the following
1. replaced the ignitor
2. cleaned and secured contacts.
3. looked for and found no obstructions in gas line

My guess is that I have a faulty pilot light valve that is not responding properly to the the electric signal when the ignitor is call for gas.

Thoughts, comments, a little help.

oncall 12-09-2012 08:43 AM

Here are just some ideas of what maybe happening from your description.

When it does light. Is the pilot flame very small or yellow. Check the flame pattern.
You may have a dirty pilot orifice and that can restrict gas flow to the pilot, this in turn might be a reason for taking a long time to light.
Also the pilot flame may just need to be adjusted, there is a PIL. ADJ. on the gas valve (remember a pilot adjusment not the burner pressure adjustment.)

You say you replaced the ignitor, did you clean the wire conections that carry the spark to the pilot also are they good and tight connections.
You might have a weak spark at the pilot asembly.

As always if your not sure then call an HVAC technican. The voltage at the ignitor will be very high.

Hope this helps

h2ocoach 12-09-2012 09:21 AM

Thanks for the quick reply.
The ignitor spark is a strong blue
the pilot flame is a strong solid blue.
I did clean and tighten all the contacts when I put a new one ignitor in.

My wife just told me that soetimes when she goes down to the laundry room / basement where the furnace is she smells a slight gas odor - NOW She tells me. So I went back down to the furnace to take a wiff - nothing. But the furnace was clicking away and then ignited. So I pull the front panel off which of course shuts the unit down and I wait a minute. I then depress the kill button and the unit starts to click and after a few clicks fires up. I do this a couple of time and each time it works just as it should. I then turn the power off and after 20 minutes try the start up again. This time it takes a very long time of clicking before the pilot lights. Conclusion: I may have a small leak in the pilot gas line that I failed to detect when I replaced the original unit. Action Plan: take the ignitor / pilot light assembly back out (have to disconnect the pilot gas line) test the hard line for cracks and re-assemble making sure to "dope" the fittings real good.

oncall 12-09-2012 09:35 AM

A small leak on the pilot gas line might be the reason. If you have a leak detection solution that you can spray on the pilot tubing from the gas valve to the pilot assembly this would help.

Also you maybe smelling the gas that is not lighting quickly when it comes out of the pilot.
Check the position of the spark on the pilot hood it may not be in the gas flow pattern and causing a hard time to light.

Hope it is simple thing like a small leak on the tubing...

yuri 12-09-2012 10:01 AM

Yep, the hood of the pilot burner can and will warp with age and get distorted. Is it the 3 wire pilot assembly/burner that you have. Post a pic of it. DO NOT buy anything other than the original Carrier 3 wire pilot burner as the other no name brands are made in China and we have had lots of problems with them not heating up properly and closing the warp switch. You can use dish soap and mix up a bunch of suds for leak detecting.

HVACTECH96 12-09-2012 10:12 AM

Some 3 wire pilots can be very touchy on how the electode is set.Some lite first spark and some take awhile.Sounds like you need new pilot assy due to extended time its taking to close switch.Have seen couple times lockout ignition contol open pilot valve but no spark, turned out to be broken solder joint at molex plug.

jagans 12-09-2012 12:10 PM

If it aint broke, dont fix it
 
What was wrong with the old thermocouple type of pilot? If you turned it to off in the spring, and then lit it in the Fall, How much gas would you actually use, and since it would be producing a little bit of heat when you need it anyway, where is the loss? I read on these posts that the life of a HSI is about 3-5 years. I can count on one hand the number of thermocouple problems I have run into in my lifetime, so why did they go from a reliable device to a POS?

Oh. and did anybody calculate how much it cost in electricity to make a HSI Glow? It a dead short, for gods sake, like a toaster.

One step forward, and three steps back.

yuri 12-09-2012 06:42 PM

Quote:

Originally Posted by jagans (Post 1069569)
What was wrong with the old thermocouple type of pilot?the wind and drafts blew them out A LOT If you turned it to off in the spring, and then lit it in the Fall, How much gas would you actually use, and since it would be producing a little bit of heat when you need it anyway, where is the loss?Where do you get rid of that heat and moisture and fumes it is a lot in a sealed combustion furnace with no chimney and natural draft?? I read on these posts that the life of a HSI is about 3-5 years.the newer silicone nitride ones are as strong as a nail and will last a lifetime in most furnaces. have lots out there that are over 10 yrs old and even the regular ones can last over 10 yrs I can count on one hand the number of thermocouple problems I have run into in my lifetime, so why did they go from a reliable device to a POS?

Oh. and did anybody calculate how much it cost in electricity to make a HSI Glow?the newer furnaces use a reduced voltage so they use a LOT less NRG It a dead short, for gods sake, like a toaster.where is that "wasted NRG going and when??:devil2:

One step forward, and three steps back.

.....

jagans 12-09-2012 09:10 PM

Really?
 
I have NEVER had a pilot light blow out from the draft created by the wind.

Good news on the SN HSI. I just installed one in my furnace.

I would be willing to bet that with the frequency that a furnace cycles in the winter months, causing that igniter to glow like it does costs more in electric power than is used by a NG pilot light that stays on.

A dead short uses a lot of juice.

I actually have a vent free gas log set in my family room that has a pilot light that stays on. It runs on natural gas, and requires no vent at all. The nice thing about it is that if the power goes out, we still have heat. That is a real consideration where power outages are common.

SO how would a pilot light that is not power vented pose any significant problem?

yuri 12-09-2012 10:28 PM

It is not a dead short it is an element which creates heat which actually heats your house.

If you serviced furnaces for a living then you would know the problems we have with negative pressures in houses, down drafts in chimneys etc etc which causes pilots to go out. I am not going to discuss my entire industry or its issues forever. There is a lot of moisture produced when you burn gas and the fumes/moisture need to leave the furnace otherwise rusting occurs. Fireplaces are thick enough and a different story. You can have pilots in stoves or fireplaces venting into a house and the amount of gases is not hazardous. Put that moisture into a closed heat exchanger and it will rust them out.

jagans 12-09-2012 10:38 PM

I did not think of that
 
Thanks Yuri, I did not think of the corrosion issue. I guess drafts are a real problem if you say so. I defer to the expert. I did put in one of the more durable Silicone Nitride? Igniters and ordered a spare. From what you say my furnace will be replaced before I ever need it, but its good to have because with my luck, mine will die on Saturday night at 1 AM.


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