# AO Smith Cyclone Xi backfires



## captainanglin

Hi Folks,
We have a job with three AO Smith Cyclone Xi units (199,000 BTU) that are only a few months old. One unit has a backfire occuring that is loud as a shotgun blast. Never ran into this before and a little frustrated with the several repair attempts so far. 

We assumed we had a gas pressure issue and made sure we were fully regulated from the 2 psi gas supply. Originally we had no main regulator but independant 7 to 11 w/c regs on each unit. The other units were working fine but we suspected this was a little hard on these non-vented regulators anc they we dumping high pressure briefly when the gas valve opened so we installed a 5-15 w/c vented 2" regulator ahead of the three. The gas pressure swings we were experiencing on start up were gone (they were pegging my manometer previously for a second or two) but the unit still backfired. Thinking the unit had a damaged gas valve we replaced it. The backfire is still there but only 1/3 as bad. Our ventings are well within specs and I can't imagine what else could cause this. The backfire comes out the fresh air intake. 

Has anyone experienced this with any of the Cyclones? The factory guys really have not been much help. One rep says get rid of the main reg. another says get rid of the three independant ones. They all say vents are the problem but they are 3" with minimal ells and less than 20'.

Would love some imput if you all have any.

Thanks,


----------



## Plumberman

Head on over to the intro section, post one up and I'm sure we will get this figured out.


----------



## Protech

captainanglin said:


> Hi Folks,
> We have a job with three AO Smith Cyclone Xi units (199,000 BTU) that are only a few months old. One unit has a backfire occuring that is loud as a shotgun blast. Never ran into this before and a little frustrated with the several repair attempts so far.
> 
> We assumed we had a gas pressure issue and made sure we were fully regulated from the 2 psi gas supply. Originally we had no main regulator but independant 7 to 11 w/c regs on each unit. The other units were working fine but we suspected this was a little hard on these non-vented regulators anc they we dumping high pressure briefly when the gas valve opened so we installed a 5-15 w/c vented 2" regulator ahead of the three. The gas pressure swings we were experiencing on start up were gone (they were pegging my manometer previously for a second or two) but the unit still backfired. Thinking the unit had a damaged gas valve we replaced it. The backfire is still there but only 1/3 as bad. Our ventings are well within specs and I can't imagine what else could cause this. The backfire comes out the fresh air intake.
> 
> Has anyone experienced this with any of the Cyclones? The factory guys really have not been much help. One rep says get rid of the main reg. another says get rid of the three independant ones. They all say vents are the problem but they are 3" with minimal ells and less than 20'.
> 
> Would love some imput if you all have any.
> 
> Thanks,


I've worked on a few of those and have had that happen. Post an intro.


----------



## Protech

Ok,first let me say that the AO cyclone Xi's are crap. I service several commercial building that have newer boilers. Some are Lochinvar and some are AO Smith. I have never been called out to work on any of the Lochinvars. It's ALWAYS the AO smiths.

The back fires I have seen so far were all caused by blacked flue pipes. The flue pipes were backed up with condensate. Also, these heaters are very sensitive to atmospheric pressure fluctuations. Inspect the flue pipes with a fiber optic camera if you have to. Also, if there was a condensate backup at any point, you may have rust buildup in the heater coils. You can clear the rust by cutting open the flue pipe a few feet above the boot that connects them to the heater on the exhaust side. Aim it in a safe direction and have plenty of fresh air exchange or a SCUBA tank. Fire up the heater and the backfire will blast a bunch of rust out of the short flue pipe. Do it a few times and that should get rid of the rust. Be ready to clean up a mess too.

The ones I have worked on were AO Smith cyclone Xi BTH-250's.


----------



## bigmosr

*cyclone xi backfire condition*

I agree with Protech in that I saw same condition in our Cyclone water heaters when I first came aboard to maintain 16 of these heaters. After taking pressure/temp readings that proved normal I noted that exhaust gasses were causing condensate at base of flue to flash. The 4" street 90 on BTH 400A has down leg that can be cleaned on a monthly PM so condensate is free to drain.


----------



## Master Mark

*what fine quality*



Protech said:


> Ok,first let me say that the AO cyclone Xi's are crap. Fire up the heater and the backfire will blast a bunch of rust out of the short flue pipe. Do it a few times and that should get rid of the rust. Be ready to clean up a mess too.
> 
> The ones I have worked on were AO Smith cyclone Xi BTH-250's.


 
that is a hell of a way to have to repair a heater, let it backfire out the top of the pipe like a shot gun blast to 
get the rust out of it... How often does this need to be done anyway???....

might I suggest if the unit is still under warranty,,,
 take a gallon of water and pour it down the chimmney... then claim it is leaking and get a warranty replacement:yes::yes:


----------



## frugalrooter

I guess we are lucky haven't had any real troubles with the ones we install yet. Guess its coming.... yaayyyyy


----------

