[user33]

I have an 7 year old Carrier 8000 that has the dreaded lockout situation where it won't stay lit on an intermittent basis. I've replaced the flame sensor, cleaned it until spotless numerous times, and I still have dropouts. I've had the furnace since it was new.

I've had the pro's over - they clean the sensor, it runs for a while, and when they leave the furnace stops working. It is the most frustrating problem I've ever seen. I've read other posts with the same problem - I haven't seen the breakthrough solution yet.

Where do I look next? It gives me a code 14 if that means anything...

Is it bad engineering or something else?

 

[NickTech]

make sure the flame engulfs the sensor, check the maniflod gas pressure with a manometer. it should 3.5" water column.

 

[rakes9720]

Be sure that the furnace is grounded properly. The control board sends current through the flame sensor, which goes through the flame and then to ground. If the board is not grounded, the circuit will not be complete, and it will not know that the flame is lit and shut off the gas, causing a lockout.

 

[user33]

make sure the flame engulfs the sensor, check the maniflod gas pressure with a manometer. it should 3.5" water column.

The flame is engulfing the sensor. I think it is a gas pressure issue. When I hear the gas come on, and I blow in the area, it lites. If I let it do it on its own, it is intermittent. Does that make sense? Could it be gas pressure?

 

[user33]

Be sure that the furnace is grounded properly. The control board sends current through the flame sensor, which goes through the flame and then to ground. If the board is not grounded, the circuit will not be complete, and it will not know that the flame is lit and shut off the gas, causing a lockout.

The flame is engulfing the sensor. I think it is a gas pressure issue. When I hear the gas come on, and I blow in the area, it lites. If I let it do it on its own, it is intermittent. Does that make sense? Could it be gas pressure?

 

[rakes9720]

It is possible that the pressure is incorrect. When a gas valve is old, the pressure regulator inside can malfunction, and cause a pressure change. Measure the gas pressure and make sure it is 3.5" w.c.

 

[Marty4164]

If you have to blow into burner area to get them all to light I would say you need to have it cleaned out. Burners need to be pulled out and washed. All it takes is a little dust in the crossovers to stop it from lighting properly.

 

[NickTech]

a seven year old furnace would most likely have inshot burners that won't collect dirt that way and the can't be "washed".

 

[Marty4164]

a seven year old furnace would most likely have inshot burners that won't collect dirt that way and the can't be "washed".

Nick you never came across an older carrier with the 3 wire pilot and seen it was burning out of only 2 burners near the pilot and the other 3 were just sending gas up the chimney??

I never used to wash inshot burners before but the company I'm at now thats what they want. There is no harm in washing them.

Inshot burners will always collect dirt when sucking air from the house for combustion. Especially in the laundry room Where alot of furnaces are located. Thats why they have the ignitor on one side and the sensor on the other.

 

[NickTech]

yeh i guess your right i was thinking along the lines of the old type of burners where the flame lays across the top of the burner. usually it's a gas pressure problem, but i'll have to give washing them a try the next time i come across that problem!

 

[eskort]

I also have this problem on a Carrier 58MVP. Its been doing it for 3 years now (1998 install). Will blowing them with compressed air work?
I notice it seems to happen more when its very cold outside, or when the temperature drops--any additional insight?

 

[NickTech]

have a pro check the gas pressure. when the temp drops so does the pressure.

 

[mdshunk]

...when the temp drops so does the pressure.

I thought I was the only one who observed this phenomenon. Of course, the gas company says that this "never happens". Sure.

 

[Ron E.]

lockout on Carrier

Would anybody troubleshoot any differently on a Carrier 8000 that is only 1.5 years old getting the intermittant lockout condition ? It actually did it within 4 months of being installed, but upping the gas pressure flow on the vavle(maybe along with some cleaning) fixed it for about a year.

It usually fails to light on the first try, igniting on the 2nd or 3rd. I have also seen it ignite, then blow out within second or two, and try again if it has not hit lockout.

(Sorry, I'm not a pro but this is ridiculous on a unit this young and now that I see it is a common problem, I'm even more ticked off).

 

[mdshunk]

Jeeze, it could be so many things. What I find so troubling is that you described that they "upped the gas pressure". While that sometimes needs done, did they actually check it with a manometer and adjust to match the data plate pressure listed on the unit? Did the unit ever fire off with a big "whoosh!"? Did the unit ever do this more than once? There's a couple of things I'd check if I was serviicing your unit. First, I'd actually take a manometer reading of the actual pressure leaving the gas valve to the main burner. Too high or too low will both cause your troubles. I'd also check for a "popped" heat enchanger. The heat exchangers in most units nowadays are just crimped, and they can pop open at the seams if the unit ever fires off with a whoosh. Also, I'd check the smoke pipe and chimney for collapse, birds nests, debris, etc. Have the burners ever been physically taken out and washed or cleaned? This has solved many problems like yours too.

Just some stuff you can check on or have them check. The biggest point I'd like to make is to have actual manometer readings taken of the burner pressure. Anything less is just guessing.

 

[747]

mdshunk

what would it mean if a furnance fired off with a big whoosh. My hot water boiler did that. I shut the switch off and turn it back on and it fired up ok. This was about 2 weeks after I had it cleaned. I had it cleaned because of that reason meaning the big whoosh. So your thinking maybe old gas line. Its orginal to my house 1963. But I have it serviced every winter. Put new circulator pump on it. Put 2 new zone a flow valves on it. Put new hydro tank on it meaning the take that pressure the system to I think 13 pounds. My plumber said its in excellent shape. Well it off now seeing how summer is here. But i'm going to need to look into problem by next winter. Don't want to come home and not have a home to come home to. :Thumbs:

 

[MechAcc]

I also have this problem on a Carrier 58MVP. Its been doing it for 3 years now (1998 install). Will blowing them with compressed air work?
I notice it seems to happen more when its very cold outside, or when the temperature drops--any additional insight?

What fault code are you experiencing?

Annual servicing is recommended. Cleaning flame sensor, removing and flushing drain trap assembly and drain hoses. In addition the rubber drain hoses inside the furnace may becoming soft with age. When this happens the tubing collapses with negative pressure developed by the inducer assembly. This allows water to back up and shut off the burners. Improper placement of the combustion air pipe on the outside of the house can result in moist air from the vent being pulled in and freezing. By chance are you on propane gas operation? If so the regulators may be freezing and reducing or stopping the flow of gas.

Have a qualified service company check all of these items.

 

[747]

Nobody answered my question

Is it because you Hvac guys have more experience with force air furnances they with hot water boilers. Actual I usual ask questions about the hotwater boiler in the plumber section. Because my plumber takes care of my hotwater boiler.

 

[mdshunk]

Is it because you Hvac guys have more experience with force air furnances they with hot water boilers. Actual I usual ask questions about the hotwater boiler in the plumber section. Because my plumber takes care of my hotwater boiler.

The big "whoosh" is delayed burner ignition, from any of a number of causes. When the gas pours in for longer than normal before it lights off, it can sometimes light off with great fury. Misadjusted gas controls and dirty burners are the usual culprit.