KBN 080--Is Spark Igniter The Flame sensor rod Plus the FS rod?

JUGHNE

Finally cleaned my own boiler today. After firing anything I usually test the flame rod sensor just to be sure.
For this KBN pulling the flame sensor lead off did not shut down the fire. Removing the spark lead would shut down gas valve and try for relight. Anyone have this happen? I know some systems use the spark electrode as FS also, but if a separate FS is connected, as is the case here, that would always shut down fire.

Solid_Fuel_Man

What happens if you leave the flame rod wire on and just pull the spark rod wire off?

JUGHNE

With FS connected and spark removed fire stays on.
Have to disconnect both for fire off.
With spark connected boiler fires and will stay on with FS unplugged.
FS is at 6 O'clock on cover and Spark at about 3 O'clock.

So it seems FS is not needed??

Solid_Fuel_Man

I'd call Loch and ask. Most gas controls I've seen in the past 5 years at least use the spark rod also as the flame rod. I just figured it's less wires and less cost to manufacture with no separate flame rod.

G Averill_2

JUGHNE, both the ignitor and flame rod do act to provide feedback to the control board. I have never personally pulled individual leads from them while in operation to see what the response would be, but yours is not unexpected.
I know this helps with turn down on startup, especially on L.P. gas. I will try this on my next startup and will advise what took place.

JUGHNE

Another point on this KBN, the rear target wall is close to being needed to replaced. There is a small Allen screw with washer holding it in place.
On a newer than this one, I was going to remove the rear target wall for cleaning. This was just a year old, the Allen screw would not budge, I have twisted off enough things to know when to stop. If it does twist off then what is the answer?

I also service a much older Munchken, it has a 1/4" (probably metric) nut on a stud which removes nicely.

delta T

@JUGHNE I always try to put anti seize on that little screw before I put it back, I have not broken one yet, but I did have one that was so badly seized that I had to actually break the target wall to remove it (it was shot anyways), and put a couple drops of rust buster and let is sit for an hour, tightened it in a fraction, then out and it came out grudgingly. I ALWAYS put anti seize on that now, would not be fun to try and drill and tap that hole for a new screw, not to mention the warranty implications. If you do break the target wall, wear a good respirator, and good gloves, keep a vacuum running while you take it out. Its not asbestos, but its not great for you....

JUGHNE

On the newer KBN it was less than a year old, screw was installed at the factory. Target wall was good, I just wanted to remove it to protect it from water while cleaning the coils.

RPK

If you buy the heat exchanger cleaning tool kit from Lochinvar, along with the abrasive wheel and metal extension, they provide a plastic guard that protects the target wall during cleaning. For years I always worried that little screw would break, but they always came out without much fuss.

Tim McElwain

Microamps can be funny. As long as there is a circuit from the pilot assembly back through the board it will prove the flame. Dual rod systems sometimes electronically look for the path of least resistance and will prove as long as there is a path back to the board. So what is happening is both the spark rod and the flame rod together are proving the flame and as long as you still have the rod to ground ratio of 4 to 1 you are all set.