Intermittent vent damper issue

DC123

I have a 2004 Dunkirk boiler with a 8158E aquastat and 6" Field Control damper. When we bought the house, the vent damper was set in the manual-ON position. When I've set the damper to automatic mode, the damper will operate correct for a few heating cycles, but then will lock itself in the closed position with the circulator running. The wiring from the aquastat to the damper looks intact to me. Any thoughts about what might be going on?

As a second issue (not sure if this may be related), the boiler will intermittently set off the spill switch (typically on its first call of the early morning). This has been going on since last year. The venting doesn't seem obstructed, though a couple folks have noted that the size, once it gets past the 6" section, becomes a bit too big for the BTUs. I've got a couple CO monitors next to the boiler that have never gone off, for what it's worth, though I recognize that even if there are flue gases spilling, they may not contain enough CO to set these off.

captainco

CO detectors don't go off unless the CO is above 70ppm for at least an hour. Are they mounted near the ceiling or the floor?

No such thing as too big a flue! You have venting issues and it has nothing to do with the flue size, unless it is too small.

delta T

"No such thing as too big a flue! You have venting issues and it has nothing to do with the flue size, unless it is too small."


If the flue is too large, a cold start with a cold oversized flue means there is more air the must be heated and displaced to establish a good draft, this can cause spillage at the beginning of the burn cycle in even a properly sized flue, and will cause even more in an oversized flue. Is there any combustion air supplied to the room? How much oversized are we talking?

The damper likely just needs to be replaced, it is 12 years old now, likely the switch inside that allows the boiler to fire once open is starting to fail, not that uncommon. I would just leave it in the on position like it was before. Not that much to gain from it really IMHO.

Steamhead

Field sells replacement motor assemblies for these dampers. No need to replace the whole damper as long as it's in good condition.

And have the chimney checked. There may be an obstruction where you can't see it.

j a_2

When it fails wiggle the 4 wire connection at the valve assembly.....very common for the connector pins to loose friction an cause intermittent failure.....sometimes a ty wrap fixes it

ChrisJ

j a said:

When it fails wiggle the 4 wire connection at the valve assembly.....very common for the connector pins to loose friction an cause intermittent failure.....sometimes a ty wrap fixes it

I would never "fix" a system like this. Holding pressure against a questionable connection is not a reliable fix. It's guaranteed to fail again very soon.

It sounds like the connector oxidizes and should either be replaced or properly cleaned with a product such as Deoxit D5.

j a_2

ChrisJ said:

j a said:

When it fails wiggle the 4 wire connection at the valve assembly.....very common for the connector pins to loose friction an cause intermittent failure.....sometimes a ty wrap fixes it

I would never "fix" a system like this. Holding pressure against a questionable connection is not a reliable fix. It's guaranteed to fail again very soon.

It sounds like the connector oxidizes and should either be replaced or properly cleaned with a product such as Deoxit D5.
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j a_2

I like your thinking. Mr. Chris....should have thought of that a long time ago....Cleaning a loose connection, sounds great

ChrisJ

If the connector is mechanically compromised which I doubt from sitting in a basement the only solution is a new connector not a zip tie.

BobC

Molex connectors SUCK, for a few dollars more you can use a cannon style plastic connector with gold plated contacts that is BULLETPROOF. Another example of what happens when the bean counters get involved with engineering.

Bob

ChrisJ

That depends @BobC Molex also has different quality pins. I'd bet you can get what's used on those dampers with gold plating. They usually offer different base materials as well such as brass and phosphor bronze.

BobC

Contact base material and plating choices matter but the problem I've found with molex connectors is usually tied to them being soldered onto a PWB. If flux gets onto the contacts it usually never gets cleaned off and in a damp location things go south. If both sides of the connection are on pigtails you are spared that problem.

You are still left with a poorly designed contact compared to the cannon style. There is a amphenol square contact that is pretty decent and it's about half way between the cost of a molex and a cannon.

You can make it cheap or you can make it good, you can't make it both.

Both

j a_2

ChrisJ said:

If the connector is mechanically compromised which I doubt from sitting in a basement the only solution is a new connector not a zip tie.</blockquote

I say zip tie and let it fly.....the cannon plugs and amphenol plugs Bob C is talking about are aircraft rated stufff...still on those sometimes the pin gets pushed back and contact becomes weak....ya gotta do what ya gotta on a fridgid day with a no heat call.....get the heat going and advise customer of findings....sometimes a simple re crimp of the pin or socket does wonders.....

SWEI

After decades of futzing about with Molex connectors, I have to agree that the mechanical design is somewhat lacking.

It is possible to design a connector that's fast, cheap, and good. The modular connector comes to mind.

ChrisJ

SWEI said:

After decades of futzing about with Molex connectors, I have to agree that the mechanical design is somewhat lacking.

It is possible to design a connector that's fast, cheap, and good. The modular connector comes to mind.

Real men bust that molex off the damper and solder the wires right to the PCB.


Sorry, it's been a long time since I made a "Real men solder...." comment anywhere.

My connector is still on the damper though I did use deoxit on it a few times to keep it clean. If I had a problem with it though, 90% chance I'd solder the wires direct.

Another nice solution is a terminal block with screws such as what Phoenix connectors sells. Sure, you have to stand there and tighten screws but your connections will be solid and yet removable.