Lennox Furnace 80UGH Not starting - http://www.hvacmechanic.com/ Forums

Original message

vtxvtx

199.126.191.113

"Lennox Furnace 80UGH Not starting" , posted Tue 2 Oct 16:30

I have an updraft Lennox 80 UHG furnace that is not starting.

When called for heat, the unit will fire relays, attempt to start the purge fan (it only turns 1/4 turn and stops, then the main blower starts and runs for about a minute. the ignighter never fires and a limit switch alarm is shown on the board.

Since the purge motor will not start, it makes sense that the limit switch alarm would go. The voltage to the purge motor is present only for a second then shuts off (the motor is OK).

The main control board has been replaced

Any theories out there?

Replies:

acefurnacefxr

75.13.50.255

"Re(1):Lennox Furnace 80UGH Not starting" , posted Tue 2 Oct 18:06

Of course its not going to start if a limit is open..when was the last time you changed the filter?

Pay no attention to fitter his threads are crossed.

22 years of HVAC service

HVAC REPAIR IS NOT A DIY WEEKEND PRODJECT we techs that know this have 20 + years in the field and we have years and years of education. Trust me if you think you know it all you know nothing compared to a experenced trained technician.

http://www.hillaryclinton.com

vtxvtx

66.222.228.216

"Re(2):Lennox Furnace 80UGH Not starting" , posted Wed 3 Oct 00:09

Thanks hillary, the advice is invaluable.

With limit switch jumpered purge motor will not start.

fitter597

67.174.0.159

"Re(2):Lennox Furnace 80UGH Not starting" , posted Tue 2 Oct 21:19:

That what it is Ace, it's not the Lennox machine that is a problem, it must be all the users....LOL

Please ignore Acefurnacefxer he hates himself for being a theft It's hard when you can't look at yourself in the mirror.

Pipefitters Local 597
" We do it right the first time"

[this message was edited by fitter597 on Tue 2 Oct 21:20]

fitter597

67.174.0.159

"Re(1):Lennox Furnace 80UGH Not starting" , posted Tue 2 Oct 17:12

1. it's a Lennox, they are prone to failures.
2. i would check the high limit if the board it showing an alarm .
Limit should be the size of a credit card with two wires on it, just above the gas control screwed into the front heat exchanger plate of the furnace, remove the two wires and jump them together, then try a start, if that works you need to replace that limit fast, try not to use the furnace untill you have one in place, could be dangerous.

Pipefitters Local 597
" We do it right the first time"

vtxvtx

66.222.228.216

"Re(2):Lennox Furnace 80UGH Not starting" , posted Wed 3 Oct 00:11

Jumpered the high limit and tested the motor for short circuit etc. (is OK). The purge motor will still not go.

Aside from the limit switch what other system checks are done before the purge motor starts, I understood that it is the first item to start when a heat demand is made?

Thanks

Houston204

98.196.66.53

"Re(3):Lennox Furnace 80UGH Not starting" , posted Wed 3 Oct 00:59

What trouble code do you have?

"Tip of the Day" Remember to remove power first.

vtxvtx

199.126.191.113

"Re(4):Lennox Furnace 80UGH Not starting" , posted Wed 3 Oct 11:41

#1 is flashing and #2 is continuously lit to indicate the limit swtich issue. Would I get this alarm as a result of the purge motor not starting or is the limit swtich the cause of the purge motor not from starting?

acefurnacefxr

75.13.50.255

"Re(5):Lennox Furnace 80UGH Not starting" , posted Wed 3 Oct 15:58

quote:
#1 is flashing and #2 is continuously lit to indicate the limit swtich issue. Would I get this alarm as a result of the purge motor not starting or is the limit swtich the cause of the purge motor no ...

You have a open limit.........until you correct that the unit will not attempt to start.....there is more then one in the loop

vtxvtx

199.126.191.113

"Re(6):Lennox Furnace 80UGH Not starting" , posted Fri 5 Oct 12:12

Fixed!!

Furnace cleaners had disconnected a t wire plug in series with the limit switch, plugged it in and ... Bob's your uncle.

Thanks for your assistance

marchvac

24.57.145.130

"Re(6):Lennox Furnace 80UGH Not starting" , posted Thu 4 Oct 20:42

If it is one of your reset roll out switch it is a little button between the two wires around your burner compartment that must be pushed in.Roll out switches can trip from negative pressure in the house such as a wood fireplace or large kitchen exhaust.

marchvac

24.57.145.130

"Re(6):Lennox Furnace 80UGH Not starting" , posted Thu 4 Oct 20:42:

[this message was edited by marchvac on Thu 4 Oct 20:44]