A. O. Smith won't fire... please help!

Hey All,

I have an A.O. Smith BTX-80 commercial water heater that I use for both potable water and radiant floor heating in my house. A year ago, an idiot developer tore down the row house next to mine and ended up doing significant damage to my house, so I drained the whole system to avoid freezing until things were repaired. Now I'm trying to get the heating system filled and running again, but have run into a problem.

So this is a power vent tank with all the fancy electronic controls. When I turn the unit on, it cycles through 3 attempts at lighting, then goes into lockout mode. In each attempt, I can see that the ignition element is glowing bright, fairly certain its as hot as it always was before.

When the power vent fires up on each attempt, about 5 seconds later I get an error code. Here's the troubleshooting guide's info on that error:

Problem:
Pressure switch remained open longer than 5 seconds after the combustion blower was energized.
Solution:
1. Pressure switch wiring is incorrect
2. Pressure switch tubing not connected correctly
3. Air intake or exhaust obstructed

This tank was working fine before, and was not effected by the damage to the house, so I can't imagine that the wiring could be a problem. I don't think anything is obstructed, but its possible. I currently have a flexible tube coming off the power vent and going straight down the side of the tank and tying into a T fitting on the 1" PVC drain that goes from the pan under the heater to the floor drain. Is this an acceptable way to run this tubing line? I do think I've gotten that error before, but it would still light and operate fine, so I just left it alone. I don't know a lot about what this pressure switch is or what it does, so not sure how to troubleshoot it. Any help here would be very helpful.


So, it does this 3 times, each time giving this error, trying to light, and failing. After the 3 attempts, I get another error code, with this description:

Problem:
System in lockout
Solution:
1. Gas supply is off or too low to operate
2. Hot surface ignitor not positioned correctly
3. Low voltage to the water heater
4. Electric polarity to the unit is incorrect - test and correct

The gas was turned off for this whole time while the house was being repaired, but it is back on now and both my stove and gas drier work fine since turning it back on. It may be possible that the valve at the street isn't fully open, but this doesn't seem to be causing any problems for the other gas appliances. I don't think the ignitor would have moved... nothing really has changed, other than the tank being exposed to a bit colder of an environment than usual. The electric hasn't changed, other than a new panel being put in while the new service line was installed (old one was cut out after damage to house as a precaution), so again, I doubt that there is any problem with it.

Any thoughts on how to correct this problem(s)?

Thanks!
Mike

Put in a proper vent and it should work.

jadnashua said:

Put in a proper vent and it should work.

Click to expand...

Can you elaborate? I have a 3" PVC vent installed up through a chimney with the proper down-turned vent terminal per manufacturers instructions, and it worked fine for 2 years. I have a 3 story row house, so 3" was required for the length of my vertical vent. There was no practical way to do a side-wall vent, as the only side wall nearby not connected to another house was the front face of the house, with windows etc.

Is this possibly a problem in my condensation drain line, or the flexible tube from the power vent (something to do with a pressure switch I think, but I don't really understand exactly how this system works)?

The pressure switch is for the air intake and/or exhaust. If the blower cannot freely suck in air and blow it out, the system will not fire. If the intake or exhaust is restricted that is the problem. Beyond that, I would recommend you call for professional help. If the safety system is bypassed, purposefully or accidentally, it could lead to a grave situation.

What's the flexible pipe going into the 1" pvc?

If the system wasn't used for awhile, there could be a bird's nest, dead rat, squirrel, or who knows what in either the intake or exhaust. The power vent pulls a vacuum and must generate pressure, so there could be both pressure switch and/or a vacuum switch that must be closed all based on the system's ability to properly move the air needed for combustion and safe exhaust.

It's a condensing unit Jim- he's talking about the condensate line.

I'll check on the outlet of the vent pipe. It has a wire mesh inside the terminal, so no animals could get up inside the vent pipe, but maybe the birds did something up in there.

There are several flexible tubes on the heater, some for condensate, one I think controls the pressure switch. I found a service bulletin from A.O. Smith about the pressure switches (manual has almost nothing about it), so I'll check and see if everything looks to be hooked up correctly tomorrow. I have a feeling the tube from the switch sensor to the vent might be disconnected, but I'm not sure. Hopefully that is all that's causing the first error.

I'm wondering if the first error is causing the 2nd one... some venting issue cutting off the gas supply while it's trying to light. Come to think of it, I think I can usually hear the gas starting to flow, and don't remember hearing that at all on my few attempts to get it to light. Also, after several attempts, I probably should have smelled a little gas if it was flowing, so hopefully fixing the pressure switch issue will solve the ignition issue.

I'll take a look tomorrow and get back to you. Thanks for the input!

The gas will not flow unless the blower is working properly,
it has a negative gas valve that the gas has to suck out of

My repairman just left...my A O Smith hot water heater stopped working correctly. The diaphragm safety switch stopped turning on the burner. There is a small orifice which extends out of the fan housing. The orifice is connected to the diaphragm switch by a small tube. The small orifice nipple clogged up and so there was no vacuum to activate the switch to turn on the blower. The repairman first inserted a small wire into the orifice nipple to clean it out.
The wire would not go through the nipple. He took a small drill bit and inserted it into the orifice. It wouldn't go all the way into the housing cleaning out the orifice. He next took the next larger drill bit and used it to clean out the orifice.
He finally got the orifice clean but the switch still didn't work. By cleaning out the orifice with the small drill bit he increased the diameter of the orifice enough so that now there is not enough vacuum in the connecting tube to activate the switch.
The orifice is press fit into the fan housing and cannot be removed! So the whole fan assembly has to be replaced! About $350 before labor.
So if a $1 part (orifice) on the fan housing clogs...it is a good chance you will have to replace the whole $350 unit!
There is no way to remove the orifice by itself. Talk about bad design...or maybe it is a good design in the eyes of the manufacturer. If the orifice had been designed to screw out for cleaning...$1 parts cost instead of $350 plus labor. A cheap part that has a good chance on clogging up forces the owner to total replace the whole apparatus!

It's definately a design decision. On the (few) I've dealt with, the pressure switch was an external piece, designed for easy replacement. Course, you had some extra hoses that could eventually crack and leak, but those were fairly obvious.

So I ran into a few problems today with the work being done on the house, and didn't have time to look at the heater as much as I had hoped.

I did check the tube for the pressure switch, and it was attached correctly, and clear of blockages.

I didn't have time to get up on the roof and check the vent terminal, though I doubt that's blocked given the mesh fitting that's in it. I'll try to look at that tomorrow.

So the tubing seems to be fine, and the wiring hasn't changed, so the only other solution on the troubleshooting guide is a blockage somewhere that I haven't been able to locate yet, or the possibility that the switch is bad. I think there's a way to test that switch in the A.O. Smith pressure switch bulletin, so I'll have to look at that more tomorrow. Maybe I just need to replace that switch, its easily removable on my unit.

The burner tries to light, which I would think it wouldn't do if the switch wasn't operating correctly... so not sure what's going on there.

If anyone's interested, here is the manual for my unit. I think they updated it since I got mine, there's def. a bit more info in there than mine had.

I just got home, gotta shower from the long day, but will post a couple pictures in a bit after I get out and get something to eat.

The cycle starts, the fan comes on, then, and only then, if the switch closes indicating the induction/exhaust system is functioning properly, does it try to light the burner. So, no vacuum/pressure where it should be, and the thing detects that, goes into a purge cycle, and retries. After a few tries, it locks out, indicating an unrecoverable error.

Checking the switch should be fairly easy...if, you know how to use a multi-meter and can follow the wiring diagram.

Yeah, that's what I mean though... I would think that at the point of the first error, it would stop everything. But it doesn't. It goes forward, energizes the ignitor element, tries to light, and fails. I can't determine for sure if the gas ever comes on or not, I don't hear it come on. I can hear a switch or something click as if to turn it on, then another click a couple seconds later, presumably to turn off the ignitor and shut down.

Sorry for the small pics...

The blower assembly. Vent goes up and to the left, then up through the roof with a proper terminal at the end. There's a condensate tube coming off of it. I've just found from the manual that there's another port at the very bottom of the fan wheel housing that should be drained as well, but it doesn't seem to have leaked at all so far. I'll have to pick up some more tubing and run a drain off of this one. There's a small tube going from the pressure switch over to the fan housing... this is installed correctly and I took it off and checked it - no obstructions there.


A shot of the whole heater. Condensate drain line has a trap loop in it, per manufacturers specs (this is taped to the side of the heater). I need to add a second one with a loop for the other condensate drain as mentioned above. These are the lines that tied into the 1" PVC drain off the pan, though I currently have them disconnected and just dripping on the floor (if the thing would run). I plan to tie the 2 condensate lines together after the trap loops and run that back to the PVC line, again per manufacturers instructions.


This is on the backside of the heater, another condensate drain comes off the bottom of this vent line. The other end of this PVC line attaches to the back of the blower. The instructions show a condensate line coming off of this, going through a little clamp on the side of the heater (higher than the drain connection, to create a trap), then running off to drain. This is how I have it set up. This line tends to gurgle when the blower is on... not sure if it should be doing that or not... any thoughts?

Try draining that line that may be your vent blockage ?

Otherwise you need a megahelic gage to check pressure and vacuum at the switches

to see which one maybe faulty !

Of course you can always just call A. O. Smith and get a local plumber trained and with

the proper tools and parts to fix it right and be done with it

On one of my older boilers, there was a small crack in the air piping which was hard to see, but was enough for the safety sensors to shut the system down because the pressure/vacuum wasn't up to snuff. It doesn't take much out of the ordinary for the safety circuts to prevent the system from running. If you can follow the interlock diagrams, and have access to the terminals, it's fairly quick and easy to see where the circuit is broken (i.e., a switch not closing, for example), then to test that component to see if it is not closing for a good reason, or is just bad. Anytime working with gas, there's the risk you might blow up the house...you may be over your head and it's time for a pro.

Yeah, I'm thinking it might be getting to that point. I'm pretty good with this stuff, but don't have a ton of experience with power vent systems. Trying to learn something in the process (and I have already), but I won't do anything stupid to screw up the safety systems in place, which would potentially cause a dangerous situation.

macplumb... which line are you referring to? The one on the back bottom of the heater? I drained out that line until it no longer gurgled at one point to see if that was the problem, and it didn't do anything different as far as errors go. It definitely has some suction coming through that line when the blower is on. After that test, I put it back into a trap setup per the manufacturers instructions... it shows it having a trap there. I was curious why it keeps gurgling though, seems like if the trap was functioning correctly, it would be silent? Maybe this is a problem? Is my trap setup not holding enough water to seal it off? Instructions say that the heater will prime the trap on its own during first full heatup cycle, but I went ahead and primed it part way, which would seem to indicate that it doesn't need to be open or closed there to fire up... Any thoughts about that?

I may still take a look at testing the pressure switch (today was another long crazy day with complications and fires to put out, and I had no time to look at the heater again... maybe tomorrow or over the weekend) based on the bulletin A.O. Smith released. If its just a bad switch, I know I can do that fix easily enough. I'll see if there is a leak on the air tubing that I can detect as well, thanks for that tip Jim. I'll also check the vent terminal for blockage when I can get a ladder set up (there is too much machinery doing its work outside to get up there right now). If it ends up being more complicated than one of those things, I'll call out the pros.

Thanks all, for your help.