First, thanks for reading this post. I have tried to fix this problem for a while but could not find the clue.

We moved in this 3-year old house for 3 months, but a couple weeks ago found that the York furnace cannot work efficient enough to keep up the heat, e.g. we set the desired temperature at 72F, but the furnace will not work continuously before reaching 72F, and consequently, the house temperature would be only 67F and could be 62F only at night. This problem is more evident when it is snowing now than without. It will restart to work for a while if I turn the power off and then on, or from the thermometer by turning the heat off and then on. From the diagnostics light, I can see 4 red flashes when it is not working (the light is green when it is working). According to the manual, it could be"this indicates that a primary or auxiliary limit switch has opened its normally closed contacts 5 consecutive times during a call for heat. With this fault code the control will operate the supply air blower and inducer. This condition may be caused by: dirty filter, improperly sized duct system, incorrect blower speed setting, incorrect firing rate or faulty blower motor." The filter is new and the best from Home Depot in less than one month.

Should I clean the furnace? Replace the motor? Or something else?

The unit is York Affinity 8T Tubular heat exchanger series Efficiency 80%.

Help! Appreciate your suggestions!

Short answer... call in a local service company. There are several things that could be tested/adjusted and we simply cannot do that over the internet and chances are you will not have either the specialized tools or knowledge to do this. No offense.

It is no offense at all, although I am looking for more challenging answers. You are definitely right that I might not have the right tool and knowledge to solve this problem. I probably have overestimated my capability even though I got some diplomats in physics and CS.

I was thinking to call a service company, but with a second thought, I decided to figure out what the problem is at first. Can anybody give me some more specific hints before I give up? Thanks.

I might have not provided enough information. If so, please let me know. Thanks.

One possibility for the fault code that the manual apparently doesn't mention-a clogged air conditioning coil (indoor). This would result in poor airflow, overheating, high-limit cycling, excessive running, and poor efficiency/high operating cost. Sound familiar?

Thanks. I will have this coil clean to see what would happen then. I will report back.

Thanks. I will have this coil clean to see what would happen then. I will report back.



If it looks like this it is real dirty

Wow. I need to check that. Thanks!

I probably have overestimated my capability even though I got some diplomats in physics and CS.

Is that like a diploma or a degree?

I applaud our DIY attitude but as the saying goes "The path to destruction is paved with good intentions". You are dealing with gas and electricity. If you do not know what you are doing you could cause serious harm and or death. Take it for what it is worth.

Thanks for your concern. Like typos (sorry, English is not my native language), mistakes are unavoidable. This explain why I am extremely careful when I am dealing with this furnace. The key is that I prefer to know something before I call and trust those "professional" service companies.

Sorry for the diplomat things. I have a Ph.D. thereore, I guess that they are diplomas and degrees simultaneously.

Thanks for more inputs though.