Another heating issue

[Gonefishing]

While the issue with the gas heat cutting off after just 5-10 seconds was resolved. It was a bad squirrel cage. It had hit the sail switch and broke the fins on it causing it not to push enough air to keep the switch activated. Everything was working fine for 2 days. Now you turn on the gas heat it runs for 10-15 minutes n cuts off. Turn back on does same thing. What the hack is going on?

[rames14]

Gone fishing, have you replaced the resettable fuse?

[Daryles]

Reading through your last thread about the problem, so far you have changed:
The sail switch
The motor
The squirrel cage, fixed it.

If NOW the furnace lights and runs then quits, it could be the black self resetting fuse. Swap it with a regular 15A blue one. Simple check.
If that doesn't help, I would remove the flame sensor/igniter and clean it. Clean the burner while you have it out.
Make sure the igniter gap is correct. VERY IMPORTANT.
Next is the high temperature limit switch. Remove, clean test.
Next is the control board. If you feel you need a new control board, order a "Dinosaur" board. Very good quality and reliability.
Download the Service manual from the files section. It has detailed troubleshooting steps.

[Gonefishing]

Originally Posted by rames14

Gone fishing, have you replaced the resettable fuse?

I sure did

[Bourbon County]

You stated that it now runs for 10-15 minutes and shuts off, then you "turn it back on". What exactly do you have to do to turn it back on? Is the furnace actually raising the temp inside the coach to set point in that time frame? When it does cut off, what is the actual temp as sensed by the thermostat? If the outdoor temps are fairly mild, it's quite possible it makes set point in that amount of time.

The ignitor is only on for a few seconds and drops out once it senses flame over a short period of time. If it lights and then relights when you restart, it's highly unlikely that's a problem. I'm not certain how an RV furnace operates, but a residential gas furnace only checks the flame sensor long enough to confirm flame and then is not checked again until it relights; the flame is self sustaining and equipment assumes it will stay lit until it cycles off.

The high limit is a possibility; it's job is to make sure you are getting good heat transfer across the heat exchanger and the furnace doesn't overheat. Contributing factors to this could be blocked vents or returns which would reduce air flow. It's just a bimetallic disc with normally closed contacts, cleaning won't help it. Mother board is a remote possibility, but most of it's work is done during the ignition sequence.

If you don't already have one, get a cheap room thermometer and check the room temps when the furnace starts and again when it cycles off. The RV thermostats are notoriously inaccurate and usually located in a less than ideal location. Mine is very close to the door and is affected by any cold air leakage around the door as well as people opening the door.

[DutchmenSport]

If the furnace kicks on ok, and then it turns off after 15 minutes, and then after a while it kicks back on ..... is there really anything wrong with the furnace at all?

Aren't they suppose to heat the area and once the temperature reaches its setting, they shut off. When the area cools down again, the furnace turns back on....... For WHAT IT'S WORTH.... there is probably only a 2 degree difference between the on and off temperature. It's very narrow in our campers.....

[Gonefishing]

Originally Posted by DutchmenSport

If the furnace kicks on ok, and then it turns off after 15 minutes, and then after a while it kicks back on ..... is there really anything wrong with the furnace at all?

Aren't they suppose to heat the area and once the temperature reaches its setting, they shut off. When the area cools down again, the furnace turns back on....... For WHAT IT'S WORTH.... there is probably only a 2 degree difference between the on and off temperature. It's very narrow in our campers.....

It doesn’t turn back on. I have to cycle through the thermostat to turn it back on.

[rames14]

Have you made sure the igniter screw tightens up? We had a stripped screw and it would take numerous times to start. On our Alaska trip, it didn’t start. Went to a mobile tech. He tried new board, replaced a few other components- no good. He was putting it back together and noticed that screw wouldn’t tighten. Got a bigger screw, instant joy. The igniter screw is also the ground screw.

[Gonefishing]

While still no heat. To date they have changed the following. Thermostat, converter, sail switch, squirrel cage, high limit switch. They have ruled out blocked duck work. I wish extended warranty would just replace the furnace and be done with it.
Furnace runs never reaches set temp. Furnace gets very hot n cuts off

[Bourbon County]

You still haven't gotten a real tech, just parts changers! At times, you have to narrow down to the best possible cause and replace a part, but wholesale parts change outs is not troubleshooting. The inherent danger is a wrong part is installed or installed incorrectly which could further complicate the situation, not to mention the $ aspect. Since you're still experiencing the same symptoms, this is unlikely in your situation.

As I've previously stated; if it burns for 15-30 minutes and cuts out, the most likely culprits are the high limit or there is possibility of a watchdog timer. The only place a timer could reside would be the thermostat, the motherboard in the furnace, or the InCommand if you have it. The high limit in most all cases will be an effect rather than a cause.

Here's a couple of things you can check: reduced air flow across the heat exchanger could be tripping the high limit. Check your airflow; here are a couple of cheap and unscientific ways: Most rigs use slots or perforations on the stair risers as return air path to furnace. Take a single (clean&dry) sheet of toilet tissue and hold against the riser while the furnace is running; there should be enough air movement to hold the TP without you holding it.

What is the temperature of the discharge air? Stick a digital meat thermometer into a floor vent after the furnace has been running for at least 5 minutes. You should see temps around 120-130 degrees.

Has anyone ever checked the gas pressure? They are rated between 10-11" WC. Unless you have a manometer and are comfortable doing this, I highly recommend a qualified tech. Operation at high altitudes will cause issues too.

Do you have the exact model number of your furnace? There are some 2 stage models on the market for RVs. I'm not sure exactly how an RV model operates, but the residential models it will always light on low stage and switch to high if the stat isn't satisfied within a determined period of time. This, obviously is to save on fuel. If it does happen to be a 2 stage, the control valve might not be switching to high when the timer tells it to.

It would also be a good test to time the burn cycles with a stopwatch. See if it's constant and repeatable.

[rames14]

You didn’t say if they changed the board or checked the igniter screw (which is the ground for the whole system). And, did they change the 15 amp fuse?

[Gonefishing]

Originally Posted by rames14

You didn’t say if they changed the board or checked the igniter screw (which is the ground for the whole system). And, did they change the 15 amp fuse?

Fuse changed, switch checked. Haven’t changed the board yet that is next. I’m just tired of the guessing game. What ever happen to being able to diagnose things. These guys are just replacing parts and guessing. Don’t know who to cal anymore. Have he two different companies send out techs.

[Gonefishing]

While finally maybe I will have heat next Tuesday or Wednesday. Tech replaced the board didn’t fix issue. Ruled out blocked duck work, ruled out any issue with the camper. Tech removed furnace took to shop completed a bench test and had the same issues. So that ruled out anything with the camper. Contact with extended warranty company. They sent out a 3rd party who informed warranty company a new furnace is needed. Warranty company approved and a new furnace has been ordered. Looks like heat is on the way.

[RMcNeal]

Just in time for the warm up. We'll be in the mid 70's by Wednesday.

[jsb5717]

Since we're just spitballin', sounds like with all of the components you've changed out that you basically already have a new furnace. If you're getting a new furnace under warranty then I guess you'll know for sure.

The only thing you haven't changed out is the gas valve, I've had one of those fail.

Regardless, if they let you, I would pull all of the parts from the old furnace and keep them as backup for future issues...they're basically new anyway.

I keep a backup for every replaceable part on my furnace so I can address it on the fly when traveling. After 3 furnace failures and 3 successful repairs I just figured I was better off having parts on hand. It actually came in handy when our friends furnace quit in 20 degree weather. They had the same furnace as us and we got them up and running in relatively short order.

[Gonefishing]

That’s my plan

[Gonefishing]

While furnace replaced. All is good now. Best tech and warranty 3d party can decide is. The baffles inside the furnace were the problem. Either way it’s working