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kkf 01-23-2007 09:43 AM

Carrier Furnace: Gas Heating Lockout
The following problem does not occur during the day, only during the middle of the night; we wake up to find the temp has dropped below the thermostat setting. The LED error code says "21: Gas control lockdown. Check for stuck gas valve relay on control or miswire to gas valve circuit."

During the day, when cutting and restarting power to the furnace via the power switch, the following cycle occurs. The fan (inducer?) comes on for about 1.5 minutes (the air blowing in the house is cold during this time). Then the fan turns off. Next, the gas comes on, the HSI glows, I hear a “click”, then the glow fades away, and the gas is lit. Then I flip the switch to turn power off then on, and the process starts again. During the night, I am guessing the gas is not coming on to be lit, so lockdown occurs.

During the day the gas lights appropriately. All day yesterday, I could not replicate the problem. It only occurs during the night, and we wake up to the lockdown and low temperature. So, HSI is good (glows always), flame sensor is good (does not shut down once the flame is lit). But something is wrong with gas flow, and only during the night (when it is coldest).

BTW, we are in Texas, and the low outside temp is only around 35 degrees F. We try to keep the temp inside at 62, and by morning it falls to 58.

Any suggestions on what I can do to before having to call the repairman? Thanks for input anyone has.

#CARRIERMAN 01-23-2007 01:20 PM

Hi kkf

If you have a manometer and can give me the incoming and manifold gas pressure I can help you diagnose problem. I am betting that either the regulator on your meter has froze up, usually caused by a tech that doesn't know to turn the air vent down so it doesn't fill with water. Or the gas valve on the unit itself has gone bad. Let me know and I will help you if I can.

Good luck

kkf 01-23-2007 02:03 PM

Carrierman, thanks for your feedback.

Here's an update: I called our local repairman, who came by and didn't even charge for the trip (what a great guy). He got no signal from the control board to the gas valve (after the HSI starts to glow, when gas should come on). As additional evidence, we did not hear the characteristic "click" of the gas valve opening. He suspects the control board needs to be replaced. However, we are both still puzzled that the probem is intermittent. It happens in the middle of the night or early morning--whenever it is coldest. He says that is very unusual. I think the problem is a bad connection from the control board to the gas valve and that the connection is worse when it is cold.

If it is simply a connection, how can I check this, and how can I fix it?

As a related point, I came across the following bulletin, which suggests my control board may have solder joint failures. Could this be related? I called Carrier and they are looking into it. See below:

"Bulletin United Carrier Corporation Technologies Carrier Residential Engineering SMB 96-0023 Subject: FURNACE CONTROL BOARD RESISTOR SOLDER JOINT FAILURES 04/17/96 UNITS AFFECTED: CAC: 58MXA, 58MCA, 58WAV, 58PAV, 58RAV BDP: 350MAV, 340MAV, 395CAV, 376CAV, 383KAV, 373LAV PAYNE: 480BAV, 481BAV, 490AAV Resco/Eventemp/Cobra: GB1AAV, GB3AAV SITUATION: A resistor solder joint failure mode has been identified on the following control boards used in the subject gas furnace. Affected Controls: HK42FZ004 (Obsolete) HK42FZ007 (Obsolete) HK42FZ008 (RCD Replacement) HK42FZ009 (Production, Open faced control board) HK42FZ011 (Production, Covered control board) Refer to Table 1 for the affected serial number ranges of the subject units. Table 1 CAC MODELS SERIAL NO. RANGE BDB MODELS SERIAL NO. RANGE 58MCA 3193A - 4595A 340MAV 3193A - 4595A 58MXA 3193A - 4595A 350MAV 3193A - 4595A 58PAV 1594A - 4595A 383KAV 1594A - 4595A 58RAV 1594A - 4595A 373LAV 1594A - 4595A 58WAV 1594A - 4595A 395CAV 1594A - 4595A 58ZAV 1594A - 4595A 376CAV 1594A - 4595A PAYNE MODELS SERIAL NO. RANGE RESCO/EVENTEMP SERIAL NO. RANGE /COBRA 480BAV 1594A - 4595A GB1AAV 1594A - 4595A 481BAV 1594A - 4595A GB3AAV 1594A - 4595A. For further information on replacing these controls please contact your supplier."

#CARRIERMAN 01-23-2007 03:02 PM

Hi kkf

It sounds like the control board in your furnace is either the HK42FZ009, or the HK42FZ011. This was the characteristics of this board. The upgrade kit has a HK42FZ013 board and needed plugs. The part number for this kit is a 325878-751, be ready to sit down, they are pretty pricy.

Good luck

kkf 01-23-2007 03:42 PM

Control Board
Sorry, I should have mentioned that I have a HK42FZ004, and yes, that is the right replacement number (325878-751). The repairman quoted me $340 for the part and $130 for labor. I can find the board online for as little as $150 (eBay) up to $240 online dealers. A few questions:
- Should I expect Carrier to replace the board for free? Maybe not since the bulletin was issued in 1996...
- Should I be skeptical of $150 on eBay?
- How difficult is it to replace the board myself? On one hand, it seems it can't be that hard (move wires from one board to the other...), but I don't want to start and get in over my head.

Thanks so much for all your help!

#CARRIERMAN 01-23-2007 04:03 PM

Hi kkf

My God thats an old board. You have probably one of the only 004's left in existance. As far as changing the board yourself, just make sure the power is off and you follow the installation instructions. If you go with ebay or any other supplier, make sure you are getting the United Technology board and not some knockoff piece of crap. I believe the UT board has a five year warranty on it, but don't take my word for it. Make sure you research it first. If you go to you can go to the tech support and let them know what you are doing. They can answer any warranty questions you have. I am good with the technical aspect, not so good with the political aspect of this industry.

Good luck

Furnace_dude 01-24-2007 07:06 AM

better be careful when changing a board, static electricity can damage the board so make sure you pet fluffy the cat after you change the board. dont do it if your the least uncomfortable about it. as far as the guys price, that is a good price for a contractor to install it, [if he messes it up, he fixes it for free. if something happens, its his fault, if he looks at it, he may find something else that needs done and you may find a guy you want to keep around for service, he came for free didnt he?!]

kkf 01-30-2007 03:10 PM

Here's the Result
Thanks for the tips, guys.

I went ahead and bought a board on Ebay for $150 (yes, it is made by Carrier) and it got here in two days. The next morning I installed it. The whole installation took about 1.5 hours, which is pretty fast considering I've never done it before and I was scared I'd break something or discharge static electricity. :) The instructions were EXTREMELY detailed and easy to follow.

If you try this yourself:
1) Be sure the problem is the circuit board. No power to the gas valve and numerous online reports about solder joint failures on this type of board made me pretty certain this was the problem. Always check less expensive possibilities first.
2) Be sure gas and power are turned OFF.
3) Be sure to ground yourself and your tools.

First, to be EXTRA careful, I used little stickers to label each wire while still connected to the old board (the instructions include diagrams of both the old and new boards; I got the label name off the old board). Then it was a simple process of removing the old board from the chassis, disconnecting wires, attaching the new board to chassis, installing the wire adapter that comes with the new board, and reattaching wires to the new board. The test sequence is easy--just use a small piece of wire to connect TEST to COMM and the furnace goes through its own check. After the check, I reconnected the thermostat wires. Everything started up just fine on a full run-through; I heard the "click" of the gas valve, then gas flowed and was lit by the HSI.

So, I saved $320 off the repairman's quote, but more importantly, learned a heck of a lot about furnaces, including what WASN'T the problem (so I'm better off next time), considering I knew NOTHING about furnaces before last week (though I do have an engineering/"fix-it" background). The several hours of researching was worth it. And I didn't even have to bother my husband about it while he was at work. :)


#CARRIERMAN 01-30-2007 04:00 PM

Hi kkf

Thank you for stopping in and letting us know the outcome of your problem. It is always nice when people post back and let the others know the solution. I enjoy the fact that you ladies are taking an interest in what we do for a living. I will be here to help as long as I can. Once again, thank you


yummy mummy 01-30-2007 04:43 PM

You sound like such a nice, helpful man.

I almost even want to have a furnace problem. :laughing:

redline 01-30-2007 05:19 PM


Originally Posted by kkf (Post 31767)
And I didn't even have to bother my husband about it while he was at work. :)


Send your husband the "repair" bill.:jester:

#CARRIERMAN 01-30-2007 08:42 PM

Hi yummy mummy

You know I and all the guys on this site love helping you. And when you need me, just give me a nudge. I will be ready to help.


yummy mummy 01-30-2007 08:57 PM

I will certainly do the "nudging" when I need you.

Atlantic is getting the "nudging" right now. He has really helped me a lot.

furnace lady 02-15-2008 05:05 PM

Could someone please help?

I am the proud owner of a Carrier 58MXA D60-F- unit. We have been experiencing intermittent heating problems with this furnace. ie. it fails at night and temperative drops below the temperature it was set at.

have there been any recalls on this particular unit? It is driving us crazy since everytime we have someone come in to check it out, it works. We finally did manage to get someone in last week who saw the problem but they were not aware of an issue with this product.


HvacWiz 02-15-2008 05:21 PM

No recalls on this unit

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