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AO Smith Cyclone Xi Commercial Gas Water Heater - BTH 400 Ignition Problem.....

AO Smith Cyclone Xi Commercial Gas Water Heater - BTH 400 Ignition Problem.....

Old 10-07-11, 04:01 AM
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AO Smith Cyclone Xi Commercial Gas Water Heater - BTH 400 Ignition Problem.....

I have 3 AO Smith Gas Water Heaters that I believe has Pop-back or Pre-ignition problems. The start up sequence makes its way through all pre-start safeties, ignites the burner and after a few seconds, shuts itself down with no diagnostic code. Upon inspection through the borner siteglass, I see/hear the burner popping, bright yellow.
Does anyone have any experience with this water heater or similiar problem. Sure could us the help. Casey
Old 10-07-11, 08:41 AM
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I need to ask first, do all three do this?

If all three and they are on the same gas line I would say its a gas supply issue. Possibly a regulator is faulty at the main by the gas meter. Sometimes in a commercial application there may be a regulator at each unit. But I would think all three would not fail. But possibly if there is a additional reguator aside from the main, then of course it could be faulty.

First step would be to run pressure tests on the gas line with a manometer. Check all W.C." before and after the units. Static, and dynamic.

A minimum dynamic gas supply pressure of 5.2" w.c. (1.29 kPa) for Natural Gas and 11" w.c.
(2.74 kPa) for LP Gas

How old are the heaters? Commercial warrantys are different. I was a AO smith rep so can help to some extent.

Also often in my trouble shooting of those heaters the installers fail to install the condensate lines properly. I often find the water heatesr filled with water in the exhaust. Which is a internal coil design hence the name cyclone.

Pull the condensate lines at each unit ( At the elbow coming off the bottom of the heater) and see if excess water comes out. Are the proper traps looped into the condesate lines? The traps need water in them. It also creates backpressure and without them the units will not work properly.

Make sure the condensates are reinstalled properly Before the system is run. CO can and will be released if not. Sickness or death can occur.

It may not be throwing a fault code, but you need to follow the on board screen and its series of operations. Sometimes you can tell by that where the issue is happening.

I also saw on many occassions, and if this is a new install, is that the installers dont understand the venting and air intake of these units. I often find the air intake is hooked to the exhaust.

Although some AO smith heaters get connected with a tee these dont and thats where installers think these units gets piped the same.

The intake at the top and the exhaust ell at the bottom are two seperate entitys. So if there are connected togther thats an issue. They will not throw a code but run in some continous loop that makes it seem like a gas issue.

This is all just a start of the first things to check.

Mike NJ

Last edited by lawrosa; 10-07-11 at 09:13 AM.
Old 10-07-11, 11:33 AM
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Yes, all 3 do the same thing, however, the heater in the middle (#2) pops at startup too, I hear and feal it at the intake, but manages to stay burning, making hot water. The 3 units, labeled 1-2-3 are piped in a first in, last out configuration to a storage tank.

The units are approx. 5 yrs old, out of warranty, but have been a constant problem since installation, we have replaced numerous ignitors, sensors, pressure switches, burner gaskets, etc.

I have checked the condensate lines for blockage, pulled the exhaust elbow off to inspect, seems dry. The one heater that is running does create quite a bit condensate and I keep an eye on that, becuase Ive had to clear them out in the past, found what it looks like rust flakes at the elbow clogging the tee off to condensate line. Each unit has PVC exhaust elbow with a tee at the bottom of them, where a rubber tube is run to a floor drain. Looks screw bally, buts how the contractor installed them. Did you mention that the consensate lines need to be trapped? because they are not.

Each unit has its own exhaust pipe, but are manifolded together approx. 6ft above the units then vented to the roof with a single pipe.

I will have the gas inlet pressures checked ASAP. All three share to same gas supply piped individually to each units gas valve, which Im not quite sure if they have regulation on them.

Thanks for your reply, still working with them, in the process of cleaning sedimate out of the bottom of them, we have no water softners. Just getting worried seeing winter in upon us.

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