Mr. Heater 75k problem keeping running

[Ryano121]

Here is the issue. Just installed the Mr. Heater 75k. Did a propane conversion because the store only sold the NG model. It will light and run fine. (BTW already adjusted it to 10" wc per the conversion instructions). It runs for about 12-15 minutes and then the top flame rollout sensor will trip. Fan is working fine, exhaust is working good as well. Plenty of combustible air in garage. Any ideas anyone. I saw one post somewhere that said that the flame was not supposed to turn the corner in the heat exchanger? Is that true? At the proper pressure, and even below the proper pressure, the flame turns the corner in all 5 tubes. It is orange by the time it turns the corner, but it still does. Any insight from anyone would help. Maybe flame leaking out of the top burner? Maybe bad sensor? Has this happened to anyone else?

 

[cowboyjosh]

In fair disclaimer Im not a furnace guy, but I have 3 that work for my electrical contracting business because when we bought a company out, they were a HVAC shop as well and we inherited a small HVAC install and service division.

Well since you said you can see the flame turning the corner, we can pretty much rule out a bad rollout sensor or other electronic issue. So my first thought is you have a cracked heat exchanger or stopped up heat exchanger. A cracked heat exchanger will allow the flame to visually "dance" and turn the corner thus tripping the roll out sensor. At any rate a orange flame is not efficient burning and continued operation can cause the heat exchanger, assuming its not cracked and junk; to soot up.

If the unit runs fine for 12-15 minutes that gives the unit and the heat exchanger to sufficiently heat up allowing any hairline crack to expand and open, let air into the exchanger and causing the flame to rollout.

Upon startup does the flame dance or does it appear normal?

 

[Ryano121]

I would say that it is not crisp and uniform like gas burner on a range or on a torch. It is blue from the beginning of the heat exchanger about 6 inches out and then turns orange as it turns the corner. All five burner tubes look the same, so I assumed that it was not a crack in the HE (or maybe a similar crack in all five? but pretty unlikely) Also unit is brand new!! Is the flame supposed to look crisp with propane? Can anyone with this unit in propane working properly and set correctly let me know what they see in the HE tubes? Does your flames turn the corner? Are they orange at the far ends? They kind of look like a torch when you first light it (before adding in the O2). Are they supposed to be crisp and pointed like a range flame or a torch?

Thanks for any help that anyone can provide.

 

[cowboyjosh]

I can't comment on how the flame looks on a propane converted unit but a natural gas flame and propane flame look pretty identical as there really isn't a huge performance difference between LP and natural gas other then natural gas does burn a little cleaner. The main difference between propane and natural gas without getting into a physics and chemistry lesson is portability, compression, energy efficiency, and cost.

Even if the unit is spanking new it can indeed come equipped with a bad heat exchanger; wouldn't be the first time. I'd probably bring the unit back to the store where you bought it from and ask for a exchange if your confident everything has been installed and adjusted correctly.

I always point at the heat exchanger first for a flame rollout situation as a problem with the heat exchanger is usually the culprit for a dancing flame and rollout 90% of the time.

Another course of action is to call a local HVAC company and have them do a once over on the unit, you might be able to negotiate that the store where you purchased the unit from to cover part of this cost, since the unit isn't working correctly. It'd be allot cheaper for them to pay for a local pro then to exchange the unit.

Keep us posted.

 

[Ryano121]

I talked to Mr. Heater tech support today. They suggested that I pinch the top end of the top burner and bend it over on itself. The flame wasn't actually rolling out, it was just leaking a little out of the top burner. I pulled the unit apart, and modified the top burner as stated above. Seems to be working fine now. Apparently the opening at the top of the top burner was letting out extra gas that was ingiting and raising the temp in the burner area enough to trip the rollout sensor after about 10 minutes of firing. We will see if this fix is the final one!!
I did a little research on propane flames and with propane, it is normal to have a yellow or orange tip, where it is not normal with NG.
This problem that they have a fix for, seems like it would occur in every case (or at least with a propane conversion). Not sure why it is not fixed at the factory.
I will let everyone know how it works over the next couple of days!! Thanks for the info.