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What needs to be done to fix a code 20 "twinning fault" on my rheem furnace

The AC works fine but when Heat is turned on the unit will not start and the control board in flashing a code 20. this is a single unit.

Posted by Im Little on

  • Jeremy Nov 02, 2020

    What was your outcome?

  • Jeremy Nov 02, 2020

    Can also be a 24volt phasing issue and a ground issue.



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Check control board make sure no wiring is on twin on board or touching it. If so remove it to correct location. If no wiring there, board replacement.

Posted on Nov 02, 2020


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  • 148 Answers

SOURCE: No heat from unit. Hear ignitors start but no airflow in house

well i need to know if the fan comes on at all if not then it could be a bad motor or board which is not uncommon but if the fan does come on and then flames go out and fan stays running could be high limit check to make sure in the bower compartment there are no wires disconnected from the blower sometimes when changing the filter it is possible to knock the wire off the board

Posted on May 19, 2009



  • 26 Answers

SOURCE: I have a goodman furnace and ac unit the fan and

Look at the contactor on the condensing unit, remove the low voltage wires to the contactor and turn on the system. If the low voltage fuse doesn't blow, replace the contactor.

Posted on Jul 07, 2009


  • 10 Answers

SOURCE: rg(bu)h-07eauer have replaced the control board will not heat

read wiring and make sure flame sensor is clean and make sure you have good ground

Posted on Oct 17, 2009


Chandler Ede

  • 1420 Answers

SOURCE: 5 amp fuse continues to blow on control board for

You have a short on the 24 volt side of the unit. Check the thermostat wire for signs of pinching or direct short.

Posted on Oct 17, 2009


  • 10 Answers

SOURCE: I have a suburban lp furnace and duotherm air/heat

I'm not sure what the problem may be but you could try calling All Seasons RV Appliance Parts & Service. There number is 1-800-344-0673 they have helped me in the past. That and there tech calls are free so it wouldn't hurt to give them a call.

Posted on Feb 16, 2010

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1 Answer

How do I fix my air conditioner/furnace

If the furnace wont work, neither will the ac. There should be a box by the outside unit. Open and pull the disconect out. Thats the switch. If ac is blowing fuses, its just to hard to say, but id look at the electrical part. Mice love it their andwill chew wires. Its sounds like a short, but worse case the ac compressor is locking up. This can be solved with a hardstart kit. The condenser fan may be shot as well, or by itself. Its possible you have a bad duel capacitor, but that usally wont let it start at all. If its a freon issue, this will kick the unit out, but not trip breakers. Be sure the coil drain on top of furnace is clear, or whater could back up and get in the electronics of the furnace, blowing the furnace fuse, not the ac. Id get a bettter tech out there and just take it off the rent. Your landlords guy should have this figured on the first try. But if you have no electrical experience, leave it be. The ac is220 volts, and mi nimum of 20 amps.

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20 year old Rheem 90 plus 120k btu furnace blower runs contantly. Furnace and AC work fine (start and stop according to thermostat setting). What is problem? How fix?

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Furnace will not blow hot or shut off

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Feb 22, 2010 | Heating & Cooling

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Rheem RKKA048JK10X Furnace/AC Unit. My rooftop

Mr. Miller,

It may be a problem with the tubing from the inducer to the pressure switches. During the night hours, condensation forms and collects in these tubes preventing the pressure switch from closing when the inducer motor starts. Check these tubes and possibly re-route so there is no sag in the middle. Try to route them so they are as straight as possible. If that is not possible, at the location of the sag, cut the line, put a "T" fitting in and attach a piece of line to the bottom of the tee with a plug to catch the accumulated condensation.

Also, have your service company check the firing rates, gas pressures and temperature rise across the heat exchanger, Any of these can also cause a problem with condensation accumulation in the pressure switch tubing.

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Having a problem with my AC/Furnace. AC was working fine and was turned on for about 3 weeks. Thursday night it cooled off and we opened up until Saturday morning. On Saturday morning the AC would not turn...

I think your problem is poor usage of the device,i.e. overloading the system. try running better cables to your furnace and ac. The reason i am lead to believe that is. If you already hired a pro to come and fix it for you,and he/she could'nt then what else could it be? in my experience ac units use electricity like microwave ovens.and power tools

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Brown wire connect to com C on terminal block in your furnance (0VAC from 24VAC transformer)
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3 Answers

I have an coleman evcon furnace when i turn a/c on the outside unit will run but the inside wont run

put the just the fan on turn off the ac and the heat and just fan on make sure the blower motor works cause thats really the only thing you utilize from the furnace in the summer and let me know
then if so does your heat work fine

May 30, 2008 | Heating & Cooling

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