Intermittent ignition failures on Hayward 400FDN heater

[cptkirk]

If I get some time I'll examine the burners tomorrow. Note, the heater does fire sometimes, just not reliably. This morning it didn't fire, but this afternoon it did. When it fails, sometimes the flame is very brief, only momentary. Other times it fires for a second or two before going out. It's interesting, in the case where it fires for a second or two, it doesn't seem to count it as a failed trial. It only goes into IF when there are three momentary flames in a row.

 

[ajw22]

You may have spiders crawling around in and blocking the burners.

 

[cptkirk]

Checked all the orifices this morning, they were all completely clear. Accessing the burners is a bigger job, requires removing the air box which has the blower mounted on top of it, so I didn't want to tackle it this morning. Heater fired up first try this morning, but the weather is drier after a bunch of consecutive rainy damp days. I'll replace the flame sensor when the part arrives, but not sure where else to go with this.

 

[cptkirk]

Heater has reliably fired every time since Sunday afternoon. The common denominator is drier weather. Sure seems like humidity is the main factor in failure to ignite.

 

[markayash]

Heater has reliably fired every time since Sunday afternoon. The common denominator is drier weather. Sure seems like humidity is the main factor in failure to ignite.

That is weird.

 

[ajw22]

Heater has reliably fired every time since Sunday afternoon. The common denominator is drier weather. Sure seems like humidity is the main factor in failure to ignite.

That points to a corrosion problem in a connection or ground.

 

[Bugman1400]

I’ve had to take some sandpaper to my sensor before. Just a few light passes. Otherwise, it sounds like either low gas pressure or crappy gas (probably with a lot of moisture in the line from the rain).

 

[cptkirk]

Grounds all seem good. Have a new sensor on order, supposed to be here over the weekend. We'll see where things stand after the replacement is installed.

 

[cptkirk]

Just installed new flame sensor. The old sensor looked OK, didn't seem to be corroded or sooted. The heater fired up fine, but not a great test because it's still fairly dry (although I did get an IF earlier today for the first time in almost a week). Tomorrow it's supposed to be rainy, so that will be a better test. Maybe it's my imagination, but ignition seemed "smoother" than before (hard to describe, just a little different sound, may not mean anything). Fingers crossed that this was the issue.

 

[cptkirk]

So far so good. We got some rain today (though not as much as anticipated). Fired up the heater four times successfully, no failures.

 

[cptkirk]

Heater still not working 100% reliably. Last night, we got some rain and this morning conditions were very humid. I can hear the whoosh for about a second, then it goes out. When this happens (whoosh lasts more than an instant), the system does not seem to count this as a failed trial, and it doesn't go into IF. It just repeats over and over until the demand is removed (lower the temp setting or disable the heater).

1. The grounds seems good to me. It's not clear to me how I could improve the ground to the burner to completely rule that out. Suggestions?
2. What are the chances this is a control board issue?
3. What are the chances this is an ignitor issue?

 

[ajw22]

How old is the heater?

You have fixed corrosion problems and seen corrosion. I am pretty sure there is more hidden causing your problems.

You can throw parts at it and maybe get lucky or start fresh with a new heater.

 

[cptkirk]

It's only about three and a half years old, so just out of warranty. The corrosion was mostly on the bond wire connection on the outside of the heater. Inside there is some light corrosion on some of the screws that hold some of the various components in place, but none on the ground to the fuse board/control board. Something is just on the edge.

 

[cptkirk]

So by 11:00 am after the sun had been out a while, heater fired up just fine again.

 

[cptkirk]

Gave the service manual for the heater another reading today, particularly the section on the ignition cycle. The symptoms don't really seem to fit a problem with flame sensing. The ignition trials last for 4 seconds each according to the manual. So if the burners were being lit but the flame wasn't being sensed, they should burn for around 4 seconds before being extinguished. But that's not what is happening.

When the heater does not ignite successfully, there are two failure modes I have seen:

1. The "whoosh" only lasts momentarily (much less than a second) and is sometimes somewhat muted. When this happens on three consecutive attempts, the heater goes into IF. This means these are counted as failed trials, which means that the flame was never sensed.
2. The "whoosh" lasts a second or two. When this happens, the heater does NOT go into IF after three attempts, it keeps trying. This means it is NOT counted as a failed trial, which means that the flame is being sensed initially. According to the manual, in this scenario the system will eventually go into IF after 10 such failures, but I've never waited that long before removing the demand so I've never seen it go into IF when this scenario occurs.

So I think perhaps I was getting cause and effect backwards. The flame isn't going out because the valve was closed (due to a sensing problem). The valve is being closed because the burners aren't being successfully lit (system is responding to a failure to light just like it should). So basically, I now believe the burners fail to light successfully when conditions are damp (not that I'm having a sensing problem when conditions are damp).

I'd like to get some opinions from the experienced folks here on what the most likely causes could be. Seems like it could be a problem with the igniter being marginal, the controller not activating the igniter as long as it should or not supplying enough current to the igniter, or maybe gas pressure is marginal. It doesn't seem like it would be due to obstruction since I don't have problems in dry conditions (and I also operate the heater for at least a few minutes a week year round).

 

[cptkirk]

Did some testing of the igniter today. The ignition cycle timing matches the spec in the service manual (20 second blower/preheat of igniter, then 4 sec before igniter starts to visibly cool when no flame detected). Have a question though. The igniter glows from the tip to about halfway down the shaft. Is that normal?

 

[1poolman1]

Be sure that a spider has not built a nest in the burner orifice that is directly below the flame-sense rod. Pull the rod out and clean it with a dollar bill, the newer the better. Don't ever use an abrasive or you will remove the coating on the rod. Learned that trick from a old HVAC tech years ago and still use it, though now I'm old.

 

[cptkirk]

I did inspect the orifices a couple of weeks ago, everything looked clean. I am pretty well convinced at this point it is not a flame sense problem, the symptoms don't match. The burners just fail to light when it is damp. I'm leaning towards a problem with the gas supply being marginal.

 

[cptkirk]

Today all day the heater would not light successfully. It was rainy and damp in the morning into the early afternoon. Finally at around 5:30 after things had dried out a bit, the heater fired up like it should. If you go back to read post #35 on this thread, I experienced both of these kind of failures today. Neither of these seem to correspond to a flame sense problem (where I believe the flame should last for about 4 seconds then go out when the gas valve gets shut off).

 

[cptkirk]

To elaborate on my reasoning, in failure mode 1 (flame on only momentarily, less than a second), it's clear the controller is classifying this as a failed trial and goes into IF after 3 attempts. In the case, flame is not being sensed, but it's not going out because the valve got closed; it just never lit in any meaningful sense in the first place.

In failure mode 2 (flame on for about 2 seconds), it's clear that the controller is NOT classifying this as a failed trial (because it does not go into IF after 3 attempts; it takes 10 attempts before it goes into IF). In this case, the controller IS sensing the flame. I believe it goes out because when a flame is sensed, the controller pulls the plug on the igniter (as stated in the manual). But the burners have not really been fully lit at this point and they go out when the igniter ceases to glow. If the controller left the igniter on for the full 4 seconds, my guess is it would probably light, but I have no way to know for sure. That's my theory anyway.

It's also clear that my gas supply has some issues (detailed in another thread). So I'm leaning towards this as the root cause of my problems.