Have a 2 yr old 90% efficiency unit.Getting code 33 while the blower runs and then code 13 when it's off. Limit switch suppose to reset in 3 hrs but has not. Flame rollout switch is not tripped so can't manually reset. This prob came about from not changing filter soon enough.

Both codes indicate a limit switch or flame rollout switch, you may have a defective switch and checking with a meter may be necessary to determine the interruption in the control circuit, good luck, Mike

Turn the power of to the unit and peck the limit swtch with a screw driver. Sometime if a unit over heats the limit will get stuck and need a little assesants in reseting. It should be a plastic switch 1 1/2 wide by 3 in tall on the upper left side or right side of your unit. It will have 2 wires hooked to it.

Check for resistance and I get 0 ohms. Its hard to tell if the switch popped as it will not push in or out and looks raised but again the picture on line look like its raised. Pulled it and looked for how many ohms it should register but its been too many years since I diagnosed small electrical. There are numbers so I assume I can find for ohms with 110 v the amp number shown and solve but have for gotten how.

Or... how many ohms should it show?

Thanx:confused:

Your checking the flame role outs now did you tap the high limit switch it see if it was stuck? The little bottons on the role outs you will know if it is out or not it will go in easy and make a small click.

OK found pie equation and there were several numbers on the part but 52A was most desernable so 52/110 was 2.11 ohms... soooo??

Could not find the limit... there is a small blower motor, not the main blower, with a circular vacuum switch with a vac line and 2 wires but no box.

Also there may be a limit down in the blower compartmant as well.

Up higher then the small blower at the above the burners is where the limit will be

http://www.hvacpartsoutlet.com/Produ...SLB1370902.JPG

The little black switch in the middle


http://img267.imageshack.us/img267/5155/dsc03382ht1.jpg

OK, will look there. Looks like the roolout is not the prob... did the car thermastat trick and warmed it up on the stove and it popped... cooled 10 sec later and I could reset it.

OK, found limit switch and it reads 0 ohms and has no adjustment screw on it.

Also, the system is suppose to auto reset after 3 hrs and won't

Latest.

Thanks for you help. Did quite understand peck (lol) did "tap" it once it was out. Followed instructions as to shut down and restart but found the 2 wires coming from the units gas valve/manual switch shut off loose... just hanging on by the plastic.

We called out the guy who installed it 2 years ago as to why we were not getting good ventilation in one room ( I used to work with him at a school dist and when he installed he damaged the intake which we called back on and in the end I had to fix). Looks as though he set himself up a service call because of the no charge call back... and I was going to have him do the maintenance... think I will do it myself.

Amyway... my wife will have heat for her daycare come Monday.

BIG Thank you