126-HIGH HEAT CYCLE ACTIVE Carrier 59MN7A060V171214

[rminoak]

Hello,

Wondering if anyone is seeing the 126-HIGH HEAT CYCLE ACTIVE and if it's related to a software update or perhaps something else going on that needs to be checked? 

It started showing up on my new furnace (1 year old) at the start of this heating season last month. Carrier 59MN7A060V171214.  The furnace was installed in Nov 2020 and ran without any issues last winter and this summer a/c season.  Filters were changed every 3 months and a new one went in when the 126 code showed up a couple weeks ago at the start of this heating season but the 126 code still shows up after the new filter going in (M1-1056 Merv 11 16x25x5).  Was going to call a tech tomorrow but doing my some online searches I saw that this might be due to a software update that happened in September 2021 and wondering if anyone might be seeing this show up and if there is a fix.

I have a SYSTXCCITC01-B thermostat with System Control Firmware Version CESR131626-04.05 (Version 4.05 software).

Found this online https://www.youtube.com/watch?v=VkLn_Cm9mLE and changed those settings this morning but looks like the 126 code still comes up for some based on the comments.  It shows changing the gas heat flow to "efficiency" and the low heat rise to "on".  Haven't let my furnace run long enough yet to see if it does anything yet on mine but will keep a close eye on it this week. 

TIA for any insight into this.  Semi-retired with building automation tech background here.

[Sergroum]

It has something to do with your furnace overheating. Either too many of your supply and return grills are blocked. Maybe you need to have duct cleaning really really bad. Or, and this you can't really fix yourself, your gas valve is overfiring and the manifold pressure needs adjustment.

It may be that it's been doing that for awhile, but remained unnoticed, slowly lessening your units lifespan. While now it is being noticed by the tstat.

[rminoak]

The ducts are clean and filters have been changed earlier than needed. I'm meticulous with that since it's easy and inspected the ducts prior to the new furnace/ac going in last November 2020. The system was measured and balanced at all the registers at all a points through the furnace when installed so I know my air flows and pressures at all points. 

For now I went back to ver 3.61 (from December 2020) and the 126 code hasn't appeared once since Monday so far. I sort of suspect that the air flow strategy that was changed in 4.05 to lower the cfm mins might be causing it for me but I'll monitor it if a code pops up again.  The code only started this heating season after 4.05 was installed. But you're right, if the code keeps popping up then it's something else.