# HELP!!!! Code 21 stuck gas valve relay



## LukeROttinger (Jan 16, 2011)

I am an HVAC Installer looking for some service help. Last year I installed a Carrier MCA in my house and paired it with a 13 sier heatpump and an edge stat. This combo has been a nightmare. Most recently I have started to get a cosde 21 on the furnace ( _stuck gas valve relay). This thing is only a year old and I can't be leave that the valve or relay has gone out already. If any one out there has any other ideas let me know.



Thanks

Luke
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## beenthere (Oct 11, 2008)

Probably a polarity or bad neutral some where effecting the board.


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## yuri (Nov 29, 2008)

If you have a stuck gas valve relay then the valve would not shut off and you should have a continuos fire and 24 volts to the valve. That is a VERY RARE code and I might suspect the board is faulty or you have a electronic conflict between your type of tstat (is it a Carrier) or other conflict. Not sure how the board checks that relay but probably they are looking at it after the W signal shuts off and doing a resistance check thru it's gas valve contacts to make sure it is open B4 the next heating cycle. Is the furnace grounded properly. Newer furnaces are VERY grounding sensitive and that can aggravate the board. Check for continuity from the metal plate it mounts on to a copper water pipe and use a cheater wire if necessary. Check from C on the board to ground with a volt meter with the power on and door switch pressed in. Should have no voltage or less than 2 volts. If more you have a grounding problem. You used proper #18 tstat wire I hope and not some crummy telephone wire? that can really mess up a board.


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## beenthere (Oct 11, 2008)

Most boards, check for it through the flame sensor. A flame signal without a call for heat would indicate that the gas valve was open when the board has it/the relay de-energized. So electrical problems can also give you that code when the gas valve and relays are good.


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## yuri (Nov 29, 2008)

And as we all know the flame sensor circuit is grounded. Feedback to/from the ground could fool it. Jeez, I feel like inspector Clouseau again.:detective:


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## LukeROttinger (Jan 16, 2011)

Yes, the stat is a Carrier. The Edge is there new communicating thermostat that contains the hybrid heat program. http://www.residential.carrier.com/products/controls/edgeprogram.shtml


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## yuri (Nov 29, 2008)

Check the items we mentioned. Does Carrier have tech support for you or do you have to be part of the preferred dealer network? If so I would try them.


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## LukeROttinger (Jan 16, 2011)

thanks for the help, I am heading to the basement now with meter in hand


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