Oil Furnace Powervent Issue

wjmst · Nov 30, 2020

I have a Tjernlund model SS2 powervent on my Trane XP80 furnace with a Beckett model A, AF series oil burner. It was installed in 2005. For the past few years, the power vent will randomly not work and it locks out the furnace. I have had the local service company out to look at it a few times, but naturally it works every time they are here. They say they clean it and nothing is wrong with it.

I was finally able to record a quick video of the issue which you can watch by following the link below:

Power Vent Issue - YouTube

There are no codes in the memory when I try to read them. As you can see in the video, the furnace is locked out. (I have an air purifier running in the background, so you can hear a fan running at the beginning of the video. This is not part of the furnace.) I press the green reset button and then you can hear a clicking sound at the
powervent, but nothing happens twice. Then on the third time the furnace fires up along with the vent. Sometimes it just clicks and never starts and therefore the furnace gets locked out. Any idea what is causing the problem or anything I can do to clue the service company in on?

Thanks for any help you can provide.

Wes

LouNY · Nov 30, 2020

With each relay click in the power vent you can see the fan blade try and move.
I would unseat and reseat any and all relays or replace them.
Do you know which command from the furnace is telling it to run,
is it coming of the blower fan or the igniter or fuel solenoid.
It could be as simple as a poor connection in a wire nut at the furnace control module,
or in the power vent.

Oaktree · Nov 30, 2020

In addition to what LouNY suggested, does the fan blade turn freely? Maybe it's binding at one spot, once it gets "jogged" a couple times it frees up enough to start?

LouNY · Nov 30, 2020

I was sitting here thinking about it and the command to run the power vent can't come from most furnace controllers.
All of our oil burners are natural drafting so we don't have any power venters, just finished the winter tuneups on them last week.

As I recall from the control diagrams That I have seen there are a few ways to wire up the power venter safeties.

Usually the furnace will get a call for heat from the thermostat,
at that point the power vent has to start and it will be a permissive for the oil burner to begin it's sequence.
So if the signal for the burner to start has to loop through a relay in the power vent which is not made until the
vacuum switch in the power vent has been activated or possible just the permission to start has to loop through the vacuum switch.
I would believe that the issue is in the power venter as the furnace should not try to fire till the power venter is running.

user.69169 · Nov 30, 2020

https://www.tjernlund.com/Tjernlund_8504105a.pdf

I bet on tired fan/blower motor dat fails to rotate when wheel stops in certain position.
Parts all available along wid 411 here
HVACQuick - Tjernlund Replacement Parts
Also available from SupplyHouse.com probably better prices

buckeyefarmer · Dec 1, 2020

I used to use a forced vent like that. Still got it, but got rid of burning oil.

Mine has a vacuum tube, that senses pressure from the vent running before it lets the furnace ignite. i.e., if exhaust not running, it won’t click the relay to let your furnace start. Sometimes the sensor goes bad.

Edit, what LouNY just said is how it works. I had to replace the exhaust fan blades once cause they didn’t create enough vacuum.

wjmst · Dec 1, 2020

Thanks for all of the suggestions. I too am leaning toward a dead or bad spot on the fan motor. Naturally while I have been home over Thanksgiving break it has been working fine, so I can't easily test anything. I'll keep these suggestions in mind.

Thanks again
Wes

user.69169 · Dec 1, 2020

Think you just walked right past yer answer. Machine comin off vacation has problem. 2005 machine got high efficiency motors and dey got known thing of growin rust between rotor & stator. Sometimes enough rust to prevent start.
Motor does start it pretty much gets rid of rust & runs good wid frequent starts.
Got similar situation wid irrigation pump only works 3 months of year.

Thought I got, dat furnace is 15 years old, and pretty dang close to end of service life for de heat exchanger.

Lookin around web, look like Trane supports de oil version any more by connecting you to local dealer
Installer info pretty good https://www.vtenergy.com/documents/23-r110101.pdf

Don't see any replacement heat exchangers for sale.

MIGHT be good thing to start looking into replacement furnace. Bandits in furnace business got no problem bleeding you out as house getting colder might make decent deal while you don't really need furnace replaced.

20 bucks buys TV camera you can plug into phone device & inspect heat exchanger yerself.