Hi, I'm new to the forum and in need of help. [B]Me[/B]: I know my way around appliances. I take apart my furnace twice a year for complete clean. [B]Equipment[/B]: Goodman GDS80453ANA [B]Problem[/B]: Codes (4 blinks) indicate High Limit Switch. [B]Sequence[/B]: Power on - "safety" blower kicks on - pressure switch check - igniter fires - system errors (High Limit). Repeat. [B]Troubleshooting [/B]done: First of all the problem has existed for ~4 days now. It has shown up a little differently leading to the current state. First it seemed like there was air in the gas line because it would "dim" and come back again. That happened a couple times and then it got into the cycle described above one time. Then, over the past few days the problem comes and goes - each time I do nothing except check the things I'm listing below to make sure I'm not missing something. It has progressively become more difficult to caress it into firing up but eventually it does fire up and then runs for hours to get the house back from the mid 50s to the high 60s where it's supposed to be. Today (right now) it goes thru the above sequence but the main blower kicks on without heat and runs until I cut power (I don't really wait to see how long it would run for because I know it's not supposed to be running at the time it is in the sequence). [INDENT]1) Checked internal temperature - measured below the Limit Switch operating range 2) Checked resistance across High Limit switch - shows no resistance 3) Jumped High Limit switch - still errors with same code at same point in sequence 4) Did all the above on Aux Limit also just because 5) Jumped out High and Aux Limit at the same time because...why not... 6) I pulled power from the board on the off chance there is some sort of phantom power (I know, I know), even though I was already cutting power at the main switch to the furnace (I have a switch inline in the 110v in the furnace closet).[/INDENT] I've done all of the above with the filter out. [B]Thoughts[/B]: [INDENT]1) With the limit switches jumpered I can rule out the switches themselves. 2) I have never seen a board throw the "wrong" error - but just because I'm stumped I checked Pressure Switch functionality and rollout switch functionality. 3) I'm down to two things - Board or Gas Valve. I don't know what a bad gas acts like but I'm thinking that it would error differently - flame without gas I think is the code it should throw. [/INDENT] Would a board problem show up so strangely? Thank you very much for any help. Super frustrated :) -John

My Nordyne/Coleman system has a heat pump and LP gas (with a fossil fuel kit). When I set the thermostat (Honeywell wi-fi) to run the fan in manual (constant on), the fan doesn't run unless the E wire from the heat pump is disconnected at the fossil fuel kit. With the E wire connected, the fan works on gas when the t-stat calls for heat, but at the low speed. It's too cold outside right now to determine if the heat pump operates normally. Is it likely the defrost board or something else? Thank you for your help! Jay