My heat from furnance stopped working G43UF

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Old 05-09-10, 07:28 PM
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My heat from furnance stopped working G43UF

I brought a townhome last year in Chicago IL.

This townhome was built in 2004.

The basement has the heat furnance,water heater and other things.

Heat was working fine all winter.

From few weeks back since the weather started getting hot, may be we would have started switching OFF the heat on our thermostat.

Our Thermostat is Honeywell RTH230B

Our furnance is Lennox G43UF, here is the link for the manual:

http://www.innovation-group.com.ua/d...gu/505064b.pdf


From 2 days the heat has become cold and I started the HEAT on the thermostat and the HEAT is not working.

I looked into the furnace and the led codes what it has is showing up like this:

Initially when i start the furnace and HEAT on thermostat:

RED LED: FAST FLASH
GREEN LED: FAST FLASH

Within few minutes:

RED LED: OFF
GREEN LED: SLOW FLASH

The above PDF manual of G43UF in page 35 shows description as follows:

PRESSURE PROVE SWITCH OPEN
OR: BLOCKED INLET/ EXHAUST VENT.
OR: PRESSURE SWITCH CLOSED PRIOR TO ACTIVATION OF COMBUSTION AIR INDUCER.

The Ignitions seems to be completely OFF.

- I am completely new to this work, can someone guide me as what I can do to fix this issue.

- I tried switch off the circuit braker and turn on , did not help
 
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Old 05-10-10, 03:41 PM
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probably the pressure switch since u stated it. its a circle with 2 wires and a rubber hose going to it. leave the hose on the switch and pull the other end off. suck on it, if u hear a click put the rubber hose back where it was(on the inducer fan motor) and see it it works, if no click, replace.
 
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Old 05-11-10, 08:31 AM
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I did this series of steps but no luck:

- turn off the circuit breaker for the furnace
- turned off the thermostat
- turned the switch to OFF position in valve (black switch)
- pulled the red rubber hose and tried to suck it, nothing happened.
- put it back
- turned ON the valve switch
- turned ON the circuit breaker
-turned ON the thermostat to HEAT mode and 75 F
-The furnance started
- the led lights were flashing fast for few minutes(both red & green)
- after sometime the RED is OFF
- green led is slow flashing

What might be wrong.

I dont see the burner in the furnace ON, that is why the heat is not coming I guess
 
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Old 05-11-10, 12:24 PM
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The furnace has a small motor to pull the combustion gasses through the furnace and a large fan to circulate air through the house.

Is the small motor turning on when the thermostat calls for heat?


The diagnostic code is telling you that the pressure switch, which should close when the small motor comes up to speed, is not closing but is staying open, which prevents the furnace from turning on. If the small motor isn't turning on, that would be one thing that would cause that condition.

I'm not a big fan of sucking on pressure switches, since it's easy to rupture the diaphragm of the pressure switch, which would ruin it.
 
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Old 05-11-10, 03:45 PM
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When I turn on the furnace and have the thermostat set to HEAT mode (76 F), then the COMBUSTION AIR INDUCER motor run very fast. But after few minutes it stops.

Right when it stops I could see the RED led OFF and the GREEN led flashing slowly.
 
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Old 05-11-10, 05:39 PM
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1) Is the flue or chimney blocked? I once paid a service man $200 just to have him remove the pipe and tell me he doesn't clean chimneys due to carcinogens. So I had to shop vac it.

2) Check the blower, it may need cleaning.
 
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Old 05-11-10, 07:26 PM
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Voltmeter test at the pressure switch. No ignition attempt will even be made if there is no 24 VAC current entering that switch, or exiting that switch.
 
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Old 05-11-10, 09:02 PM
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Originally Posted by geo8rge View Post
1) Is the flue or chimney blocked? I once paid a service man $200 just to have him remove the pipe and tell me he doesn't clean chimneys due to carcinogens. So I had to shop vac it.

2) Check the blower, it may need cleaning.

@geo8rge:

1) Can you look at the PDF link in my first post and let me know where exactly is the flue or chimney , you are talking about. FYI I am new to all these stuff, still a rookie.

2) Which blower and where is it ?
 
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Old 05-12-10, 11:51 AM
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From figure 1 You have 2 blowers. I would think either could be fouled. From the pictures you can visually inspect both of them, get a bight work light. I see something called blower access door. You probably can reach in and either look at the blower wheel, or try to scratch some of the filth if any off with your finger nail. It should be clean. That is why you need that filter. There should be no build up on either blower wheel. It is similar to 'icing' causing an airplane crash, it takes very little to make the blades of the blower useless.

As to the flue it leads to your house's chimney. It is possible debris is blocking the exhaust. It may have collected in the bottom of the chimney. Use a mirror or video camera to see if the view to the top is unobstructed. Replacing the flue can be difficult. On my set up it is a bit of an IQ test each time I do it. If you are female you may lack the physical strength to get the flue pipes back together. If you force things you may damage the connection to the chimney.

The sheet metal parts cut and scratch skin very easily. There are also safety issues as to dust and ect generated from the cleaning process. While there are no specialized tools having some infrequently used tools like a punch are important. If you know a handy person, flipping them $50 or $100 might be a better idea especially if they have their own tools.

If you experience the same problems I did:

Tools: Punch to drive motor shaft out of blower wheel. Heavy duty shop vac to clean stuff without trowing too much dust. light duty pressure washer for the blower wheel, be careful not to strip paint. A heat gun to dry it quickly if the sun is not out. Ratchet set for the sheet metal screws.

You will likely have to disconnect some electrical connections and unscrew things. Make sure you are very methodical and do not lose or forget how to put it back together.
 
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