Limit Circuit Open or External Load On "W"

And how does it get fixed?

My heater only 5 yrs old is blowing nothing but cold air. The red led light blinks once, pauses and blinks again. It is electric ignition (forced air). Any help would be appreciated. It's cold. I have had 3 different HVAC people look at it. All gave different answers. One of them actually works for the local gas company.

Your error code is telling you that you have a safety limit string open, meaning either the main temperature limit/ safety has opened due to an over temperature condition, or a "roll-out" safety is open, both will shut down the unit... and only the main blower will run to cool down the unit. Now, you also mentioned an "external load on the W terminal of the fan board... this can be caused by a number of issues. One is a high 24 volt draw on the R & W wires that call for heat to the unit through the T'stat. The first check that should be done is... do you really have a good 24 volt transformer in this unit? Then with the power off to the unit, take off all of the wires to the fan board from the T'stat, and put a jumper on R & W.. Power up the unit, it should run, if it does with no error code your problem is in either your T'stat or wiring to it. NOTE: this jumper wire is ONLY for a test. If you don't feel that you can perform these tests, call a HVAC tech for troubleshooting...