Loud pop before the damper kicks in (steam boiler)

k60

I just had a new Burnham Independence IN5I 140,000 (KIN-5) steam boiler installed. It has been running for 6 weeks. Before the damper kicks in and the the boiler fires up, there is a loud pop. It sounds like a bit like a balloon popping and is immediately followed by the squeaking of the damper. It doesn't happen every time the boiler fires up. It happens maybe a third of the time.

The installer came back to take a look but it unfortunately didn't make the sound while they were here. My guests sleep in the room next to the boiler and it is loud enough to wake them up so I can't have guests sleep there anymore. Any idea what this is and how to stop it? Thanks.

JUGHNE

Damper could be binding up and releases with a snap.
It can be manually locked open for a few days and sees if the problem goes away.

k60

Thanks @JUGHNE . It is a GVD-6 and it doesn't appear to have a switch to manually hold it open so here's my plan. I'll wait until the cycle begins and the damper arm is vertical, then I'll cut the power to the boiler. Then, I will unplug the damper motor. Then, I'll turn the boiler back on. What do you think? Would that be safe for the boiler?

SeanBeans

Check the screws holding the damper to the hood, and the screws holding the first piece of exhaust to the damper.. maybe installer used too long of screws and it’s getting caught but then Releasing with Force..?

JUGHNE

What Sean said.
Also there may be a switch under the cover.
As for your unplug plan, the gas ignition needs to get that signal that the damper is open. That cable would send that signal.

Zipper13

Not sure you can just cut the power to it. I think the boiler needs to sense that it's open before it will fire. Mine got fried and stuck open, even though it was open it wouldn't turn on until I replaced the whole damper. it was an easy swap out - just watch out for the screw length! Pop the shell off the dampeer motor and look for the lock open switch. If I remember correctly, I think it's possible to cover the switch up if the shell is put back on wrong and out of alignment. On mine the squeaking is from the little flexy metal fringe around the damper valve disc rubbing on the inside of exhaust pipe as it rotates open/closed - they help seal out drafts better when closed. Might be possible to trim them?

SeanBeans

I use 1/2 screws max

k60

I don't see a switch to manually hold it open.

Zipper13

On your second picture, I think it;s on the right near the blue wire. it's an electric switch. If I'm wrong, someone please correct me, but I think they way it works is that it should slide to lock the motor in its current state. So if you engage it when the damper opens it should stay locked open even once the burner shuts off.

Zipper13

https://s3.amazonaws.com/s3.supplyhouse.com/product_files/GVD-6PL-brochure.pdf

page 2 notes the service switch.

k60

@Zipper13 Yep you're right. I couldn't see it because I couldn't fit my head in that spot to look. I slid it forward. Now just waiting for the next cycle.

k60

It is still making the noise despite the damper being locked.

k60

I have noticed that when the thermostat is set to 75 and it is running normally, it makes the pop. But when I turn the thermostat way up immediately after the boiler finishes the cycle, no pop.

EBEBRATT-Ed

@k60

If you can duplicate the popping get your installer back there and show him

k60

The installer came back to take a look but it unfortunately didn't make the sound while they were here.

Zipper13

Gah that's a pain that it didn't make the noise with him there.

This still sounds very similar to noises that I've heard and fixed on my damper so I'm still kind of stuck on that as a possibility. Beyond that, I'm out of my realm of knowledge. I tested my lock open switch last night. With the boiler off, It did not immediately open the damper when I hit the switch. but next time the boiler tripped on, it opened and then stayed open.

You can verify that it is open by looking at the end of the axle that the damper rotates on (your first picture, left side - the opposite side of the exhaust pipe from the motor and electronics) - it should look kind of like the end of a flathead screwdriver - that "screwdriver" edge should be in line with the pipe when open and perpendicular when closed. The damper is a rotating disc - like flipping a penny. It opens/closes every quarter rotation. If it happens every other time the boiler runs, then to me, it suggests that there is an obstruction catching only one side of the damper disc doohickey inside.

So I'd still give it a few more cycles with it locked open (and visually confirm its locked open) and see if you still hear it.

After that, though I'm out of ideas

k60

The damper is definitely locked open. The switch held it open.

I was upstairs and noticed that when the thermostat clicks on, the boiler pops at the same time (it's that loud that I can hear it on the next floor). I wonder if it's an electrical issue. Does anyone know what are the first things that happen when the boiler receives the signal from the thermostat - prior to the damper opening?

JUGHNE

Perhaps a relay is closed to start the process.
Although I can't imagine one popping that loud without letting the smoke out it.
The pop happens well before the burner lights??

k60

Yes. The pop happens at the same time the thermostat clicks to start a new cycle. Usually immediately followed by the damper opening. Every 30th time, it pops and the damper doesn't open right away. The burner lights 20 seconds later.

Could the relay be making this noise?

k60

I had a plumber come out again and was able to reproduce the noise. He said it was the relay. He couldn't explain why it only happens when the thermostat kicks in after cooling. But he was sure it is the relay. Thanks everyone for all your guidance.

Steamhead

That boiler has an "isolation relay" mounted behind the front panel. It is a Honeywell R8222 type and these can be loud. The thermostat operates this relay, which then sends power to the damper and then the gas train to fire the boiler.

I've replaced these with those little RIB electronic relays to quiet them down.