[snigadnol]

Toward the end of a heating cycle, the burners would shut down and the fail code would read "open limit switch". The repairman said the limit switch was faulty and installed a new one a couple of days ago. It seemed to work fine until this morning, and now it's doing the same thing as mentioned above. What's up?

[wheatnbarley24]

You need to make sure your filter and cooling coils are both clean. You also need to check your vent pipe for any obstruction

[labman]

The control board could be going bad.

[snigadnol]

Thanks for all the advice. Here's an update:

I had the servicemen back in to investigate. The cooling coil was clean. The limit switch was working properly. The vent seemed clear. Then we tried running the furnace w/o a filter in, and the limit didn't open - everything seemed to work just fine. The service guys think that probably the return ducts are just adequate to provide the needed air for the plenum. I had a higher quality air filter, but this also reduced the volume of air that could be pulled into the plenum, so things would get too hot. They suggested I use a cheaper, lower quality filter and just change them more often. The other solution would probably be to add more return ductwork to feed the furnace.

So the furnace is working, but does anyone out there have any other suggestions so that I might be able to use a better filter?

[labman]

Usually the blowers have several speeds available selectable by changing jumpers on the control board. If the air flow is marginal, the furnace may not be operating as efficiently as it should. You will need the schematic for the furnace and some time to figure out changing the jumpers yourself. You might talk to the technicians too. Perhaps if it was as simple as that, they would have done it. May need a bigger motor.

Could look into an electrostatic filter, no restriction and very efficient filtering.

[wheatnbarley24]

What size is your return air? What size unit do you have?

[caibuadday]

[QUOTE=wheatnbarley24]What size is your return air? What size unit do you have?[/QUOTE... you could expand the surface area of the filter (reduce obstruction) by install "V" shape filter rack... *** instead of single filter; V filter rack use 2 or more filters...