Thermostat (home) question/issue

[Vigilant]

Ok, the problem has started again. The board on the unit is flashing a code, which is three quick blinks followed by three long blinks.

sounds like it was trying to send an SOS and was stopped before it finished. Sorry, had to.

 

[VUPDblue]

So either the high limit switch is bad or there’s not sufficient airflow.....

 

[churchmouse]

So either the high limit switch is bad or there’s not sufficient airflow.....

Airflow would have been apparent from the start. If the filter is clean and the returns are not blocked and the fan stays at speed it should be OK on he flow angle.

 

[VUPDblue]

Yeah the current filter has been in there about 3 weeks. The fan sounds fine and doesn’t appear to struggle. So can I presume the high limit switch is faulty?

 

[churchmouse]

Yeah the current filter has been in there about 3 weeks. The fan sounds fine and doesn’t appear to struggle. So can I presume the high limit switch is faulty?

Yes. It should be easily accessed. It will most likely be just north of the burners in the front panel. The rest of the limits should be manual resets.

 

[VUPDblue]

Alright then. I guess I’ll get one ordered.

 

[churchmouse]

Alright then. I guess I’ll get one ordered.

If you have any issues you have my number. No worries.

 

[VUPDblue]

There are three switches called “limit” switches in the schematic. I’m not clear which one it would be.

 

[VUPDblue]

The two near the burners are called “manual reset rollout switch” and the one behind the gas valve is called the “main limit switch”


Im pretty sure the one I need to replace is the one behind the gas valve.

 

[Tanfodude]

filter gets replaced every 6 weeks, I have an amazon subscription for that. I am going to try and look for a code on the board here in a bit when I get home.

Wow, every 6 weeks? I do mine every 3 months and its just slightly greyish. Maybe I'm doing it wrong.

 

[jkaetz]

Wow, every 6 weeks? I do mine every 3 months and its just slightly greyish. Maybe I'm doing it wrong.

It's really all about airflow. The furnace filter is exactly that, it filters the air going into the furnace (think pet hair, large dust particles and other things that will coat the blower, burners, and AC coil. It is not a whole home air filter. It needs to be replaced regularly because as it gets dirty it reduces airflow through the system. If the system looses enough airflow it will overheat the burners and trigger the high limit switch. In cooling season it could freeze the AC coil. If you use the 4 or 5 inch wide filters you can go longer before changes as they have more surface area to catch dirt and don't reduce airflow as dramatically as the 1" wide filters. The MERV ratings play a part as well. The higher the MERV rating the smaller particles are filtered. This sounds great to most people, but it also further reduces airflow through the system even with a clean filter. As you might guess, these filters usually cause the above mentioned low airflow problems. The loss of airflow can be measured if you want to go that far. Measuring will allow you to truly determine when a filter needs to be replaced and if you can use the higher MERV rating filters.

 

[DoggyDaddy]

It's really all about airflow. The furnace filter is exactly that, it filters the air going into the furnace (think pet hair, large dust particles and other things that will coat the blower, burners, and AC coil. It is not a whole home air filter. It needs to be replaced regularly because as it gets dirty it reduces airflow through the system. If the system looses enough airflow it will overheat the burners and trigger the high limit switch. In cooling season it could freeze the AC coil. If you use the 4 or 5 inch wide filters you can go longer before changes as they have more surface area to catch dirt and don't reduce airflow as dramatically as the 1" wide filters. The MERV ratings play a part as well. The higher the MERV rating the smaller particles are filtered. This sounds great to most people, but it also further reduces airflow through the system even with a clean filter. As you might guess, these filters usually cause the above mentioned low airflow problems. The loss of airflow can be measured if you want to go that far. Measuring will allow you to truly determine when a filter needs to be replaced and if you can use the higher MERV rating filters.

My system uses the 4" filters and I only change twice a year. Basically when I get my semi-annual checkups (AC and furnace). And as for the MERV rating, I pick a fairly high one (like maybe 9 or 10), but not the super-high value, because I figured they would restrict airflow, but also become clogged more quickly.

 

[VUPDblue]

I picked up a 4” filter today and replaced the 1” I have been using, hoping it would increase airflow and maybe cure my issue. It didn’t.

 

[jkaetz]

I picked up a 4” filter today and replaced the 1” I have been using, hoping it would increase airflow and maybe cure my issue. It didn’t.

You've likely already ruled out the filter but the quick way to test is of course to simply remove the filter temporarily.

Given what CM said I think you're on the right track with the "main" high limit switch.

 

[churchmouse]

The two near the burners are called “manual reset rollout switch” and the one behind the gas valve is called the “main limit switch”


Im pretty sure the one I need to replace is the one behind the gas valve.

That would be the auto reset high limit.

 

[VUPDblue]

I just replaced the high limit switch. Guess we’ll see how it goes.

 

[churchmouse]

If it continues hit me up.

 

[VUPDblue]

It continues. Currently rebooting now. Dammit