TRANE XV90 PROPANE FURNACE PROBLEM:

snak1e

Approximately twice a week my trane XV90 high efficiency propane furnace (10 years old) will blow cold air, the thermostat is calling for heat and the fans come on but the burners do not light. If I do not intervene the fan will continue to blow cold air for about 30-45 minutes and then the fan goes off and after a few minutes the furnace will recycle and the fans come on, the burner lights and everything is fine. If I intervene while the furnace is blowing cold air I can turn the power off wait a few minutes and turn the power back on and the fans come on and the burners light and everything is fine again.
The furnace has not yet failed to start up on it's second try but I am concerned this might happen. I had the local service professional out to check the problem and he cleaned the ceramic ignitor and also cleaned the burners with a wire brush. This did not change the problem so I installed a new trane ceramic ignitor and needless to say this did not help either. I had the same service man out again and he ordered and installed all new burners and this also did nothing to change the problem. Now the service man has indicated he would be unable to diagnose the problem unless it was occuring while he was here.

I need HELP-- Has anyone out there had experience with a similar problem or have a clue as to what might be causing my problem. Any help would be greatly appreciated.

snak1e

Tim McElwain

Get rid of that service tech first. I wonder how he cleaned the hot surface igniter. Have him reimburse you for the new burners.

Furnaces will automatically bring the fan on and run when one of the limits on the furnace opens everything from the blocked vent switch, roll out switch, auxillary switch (located in the fan compartment), pressure switch any one of those switches opening will cause the fan to come on. Make sure the filter is clean and that there is no blockage in the condensate line.

If there is overheating or a premature failure of the auxillary switch in the blower compartment this can happen. What then happens after a long running time the switch will re-make hence your problem.

Your furnace has what is called "soft lockout" it usually on most models is one hour. It occurs because after several attempts to light the furnace shuts down and then one hour later will try again.

snak1e

Hi Tim: Thanks so much for your help, I appreciate it--
I have washable reusable metal filters in conjuction with a honeywell electronic filter and I washed them just recently so they are clean. Lots of water is coming out of the condensate
line but I do have a dehumidifier hooked into that line so I will check inside to make sure it is clean and open. I don't know how to check the switches you alluded to or exactly where they are located. If I can obtain a service manual for this furnace will that be helpful in showing how to check these switches?

Another question-- this furnace has a ceramic flame sensor which I have replaced; does it also have a hot surface ignitor and if so where is it located in relation to the flame sensor and how should I clean it? This furnace is a 4 burner unit.

snak1e

Tim McElwain

You need to get an authorized Trane service tech to look at your unit. The igniter will typically be located near the first burner to get gas or in your case with 4 burners it may be located between the two inside burners. In your case all the igniter does is light the burners so take a look inside the front of the furnace and see if when you initiate a call for heat you see it glowing, if not then it may need replacing.

John Mills_5

What code is the board flashing? Look how many blinks in a row from the red LED. Usually there's a little 1" plastic "window" in the blower door so you can see it.

If you can see it not lighting, someone needs to check manifold and line gas pressure.

snak1e

John--- Next time I am home and catch my furnace in the cold air blowing mode I will try to count the LED blinks and post it here.

snak1e

Randy-LeeBraman

Listen to Tim he is the guru of gas,there is no way to clean a hot surface igniter,and i bet you didn't need those burners.As tim said one of the limits is probably tripped and when you shut it off and back on it resets.Again get a Trane tech service guy there not Bubba!

Matt_67

Actually I would guess that he likely cleaned the flame sensor and not the igniter. If stainless burners were not installed at the time of the install the steel burners often corrode at the flame spreader on propane installs and if that was the case I would also have put new burners in the furnace. Do you know if the service tech did a temp rise or checked gas pressure? He would have needed to use a meter to do either properly.

snak1e

I was with the service tech each time he came and I don't recall seeing him use a meter of any kind.

snak1e

unclejohn

Seems to me there is a problem with Trane furnaces with the plastic plug[ Molex plug ] that goes to the limit switch on that furnace. Try by passing the plug, I think the wires are yellow. Just get rid of the plug, the hi temp limit will still be in the circuit and protect against hi temp.

snak1e

Hi -- I was home tonight when the furnace started blowing cold air-- I looked at the red LED light and it would flash twice pause then flash twice again and pause and continue to do this until I turned the power off, waited a few minutes turned the power on, then the fan came on, the burners lighted and everything was fine again.

snak1e

unclejohn

Some where on the furnace [normally on the inner doors ] is a chart that will tell you what the two flashes mean.

Matt_67

Two flashes is lockout on recycles or retries. They can be a little tricky to troubleshoot if you don't catch it happening. The tech needs to start with basics - inlet and manifold gas pressure, new flame sensor, check molex plugs, flame signal,etc. Finding intermittent problems can be daunting.

snak1e

Hi everyone----Last night I removed the two rear panels and Matt was correct ,two flashes on this furnace according to the decal on the panel indicates SYSTEM LOCKOUT (RETRIES OR RECYCLES EXCEEDED). I cleaned the entire furnace good with a shop vac-- there were some dried tree leaves in the outside fresh air intake pvc pipe next to the course metal screen where the air enters the furnace. It looked like a real job to remove that screen so I took a wire and kept poking it through the screen to break up the leaves then pulled them out with the shop vac-- two hours later I had them all removed. There wasn't any water in the unit. I also removed and cleaned the flame sensor--it had some black crud baked on it. I could not identify the molex plastic plug that unclejohn spoke of. Hopefully I did some good, if nothing else I am gradually learning more about how the furnace works.
Thanks to everyone for your help.

snak1e

Doublewide

I've had this problem for several years. Always seem to get better after a cleaning. The last tech pointed out to me that the outside air intake was getting some leaves in it, just enough to restrict the airflow . Removed the leaves, problem solved.

icesailor

Leaves:

I have a friend, a really good gas service guy. He told me of some equipment he had that drove him nuts the same way that one has. When the furnace started, the leaves blocked the air flow on initial start up. When it would fail, the leaves would fall into a different configuration. Upon re-start, the different configuration let in enough air to re-start. After a very long off, the leaves might fall back into a position to severely restrict the flow.

Always check for leaves. Especially if there is no screen on the intake.

snak1e

Hi--
I thought about putting a screen on the outside air intake but was reluctant to do this for fear of reducing the air intake. Do you think I can add a course screen over the outside air intake pvc pipe without reducing the air intake to a problem level?

snak1e

icesailor

Veissman's had a 1/4" to 3/8" mesh screen for their exhausts a while ago. When I used them.

Don_197

You found your problems.....they were the following 1) The leaves...... 2) black crud on the flame sensor.... NOW the REAL question is DID THE TECH CLEAN THE SENSOR when he was there or the ignitor? (ignitors don't need cleaning) because if he did NOT FIRE HIM AND GET YOUR MONEY FOR THE CALL BACK!!! If he did...... you most likely have an LP regulator issue causing a bad burn, instantly fouling your flame sensor.......you shouyldn't have to clean it more than once a year if the appliance is burning correctly (leaves blocking or partially blocking the intake could have caused a bad burn too). These furnaces are brain dead easy to work on and diagnose........any "professional" that doesn't do it correctly needs to be paying for his own service calls until he learns his job (I always paid for mine..didn't charge the company or the customer when I knew that I had no idea what was going on....but have never even heard of a tech in the last 10-15 years doing that....different mindset these days). You should have a copy of the service ticket noting the state of the filter, humidifier pad, condensate lines and pump, temperature rise, incoming and manifold gas pressures, amperage of the motors as compared to nameplate, and resistance of the ignitor AND THAT THE FLAME SENSOR WAS DIRTY AND HAD TO BE CLEANED.......(and a REALLY good tech will measure dc microamps of the flame signal as well.) Too many slamma jammas these days.......in, out, paid, and gone.

drhvac

You definately need somebody who knows what they are doing. You already cleaned the flame sensor so I'm assuming your microamp signal is good? That needs to be checked with ameter. You could have a partially restrictricted condensate trap which is causing the pressure switch to open. It could be allot of things wh

drhvac

allot of times with the 90% furnaces, erratic problems happen because of a dirty condensate trap. If the water can't drain out quick enough, it may back up and cause the pressure switch to drop out, especially on colder days when more water is produced. An experienced tech could find this problem by taking a reading on the pressure switch. If the pressure switch is designed to open at .40, and your reading .45, well that is to close to the break point, and would lead me to checking the trap. A good tech should do that test, temp rise, check gas pressure, and do a combustion analysis. One of those test usually finds the erratic problem.

icesailor

Think SMALL leaves. Like Boxwood or hedges that drop their small leaves.

Not the great bib fall leaves like Oak and Maple that you need a big rake for.

billinwv

I had the exact same symptoms on the same Trane furnace as snake1e including the breaker reset that worked every time. Mine was caused by the burners not firing in sequence fast enough so that the flame sensor shut the unit down. The diagnosis was done by turning the gas off then on 5 or 6 times until the problem happened. The fix was to clean the gas nozzle "wings" where the gas transfers from one nozzle to the next. There was just enough soot built up over time to block the flow some of the time. It took me three mechanics before I found one that had the same symptoms in a previous job and knew what to check.

Visian

This thread was very useful as it describes the problems we are having. Heater works but then will randomly start blowing cold air. Turning heater on and off via thermostat almost always gets heat back on. Blinking lights: I see 40 green blinks, then one red... in a repeating pattern. Our hot surface ignitor & flame sensor was replaced 1 year ago... the tech actually had the nerve to charge $345 for the part (that in addition to a $225/year "maintenance" contract. We fired them). Can anyone tell me where the fresh air inlet is? I'd like to check it for leaves and/or other obstructions. If that's not the problem we will call in a licensed Trane tech. It is entirely possible that our burners need cleaning.

One other note, we recently had a standby generator put in, fueled by the same line that serves the heater, however, the problem was occurring prior to that work being done.