Noise from hydronic baseboard heating, when boiler is firing

NotBob

We've lived in this house for about 5 years, and the hydronic baseboard heating has worked well, and it's been quiet. (There is a little bit of thermal expansion "tinking", but it's completely fine, almost reassuring.) However, this year the system is making a deep rumble-rattle noise. After some observation, it seems to only be happening then the boiler is firing/heating-up.

The full sequence is this...
You're in the living room, at the far end of the house from the boiler. You start to hear a low rumble that slowly gets louder and louder. Some of the baseboards will start buzzing a bit, starting with those furthest away (closest to the boiler), then it works it way to the ones closest (furthest from the boiler). This takes maybe 2-3 minutes. Then suddenly, it stops.

If you stand in the boiler area while this happens, it exactly coincides with the boiler hitting it's low temperature point and turning on, then ending when the boiler hits it upper temp and turns off.

We have 3 heat control loops in the house, and this only happens on one of them. The other 2 circuits remain quiet. The noisy loop is the furthest from the boiler and has the highest elevation.

I've read through some of this forum. I'm thinking the cause may be the expansion tank having lost pressure. I don't see any leaking but at least one of the relief valves dumps directly into a drain so I can't see if it's wet. I'm fine with calling in someone to do service, but I like to have an idea what's happening before I do.

Can anyone help diagnose this? First things you'd check? Thank you!

STEVEusaPA

Might be just air. Not enough water in the system. Can you bleed/purge that zone (with system off)? Or maybe a circulator cavitating.
Does it do it when this zone and another are calling at the same time?
I wouldn't initially point to the expansion tank.
Can you show a picture of your near boiler piping?

NotBob

Thanks for reply.
"Might be just air. Not enough water in the system. Can you bleed/purge that zone (with system off)?"
It's not obvious to me how to go about that. No idea if/where I have bleeds. Would have to look by the baseboards.

"Or maybe a circulator cavitating."
Once the boiler shuts off, everything is quiet, and the loop continues to heat. Pump is quiet. I don't think so.

"Does it do it when this zone and another are calling at the same time?"
I would have said "yes", but I just created that situation and although I heard the startings of it (the distant low rumble), it didn't get noisy in the living room like it can.

It's tough to get good photos in the area, but I'll post a few up.

HomerJSmith

What kind of boiler? Cavitation? I'd be surprised.

You have more than one pressure relief valve?

Ironman

What’s the pressure on the boiler gauge when the system is cold?

NotBob

It's a 50 yr old house, so it's a bit messy. Here's an overall...

NotBob

Ironman said:

What’s the pressure on the boiler gauge when the system is cold?

Dead cold, don't know. With the gauge on the boiler at 130, it indicates about 8 psi. At 150 it's about 10psi. (The scale on that gauge is 0-90, and the pressure never seems to change much, so not sure how accurate I am with that.)

NotBob

HomerJSmith said:

What kind of boiler? Cavitation? I'd be surprised.

You have more than one pressure relief valve?

No, looking closer I see one pressure relieve on the boiler (water heater style). That's it. I mistook something else for another.

Boiler photo attached. Don't see a model number anywhere.

NotBob

mattmia2

Isn't the expansion tank supposed to be with the inlet up? I don't think it is your problem, but I don't believe it is right. Do you know what the pressure was say last year?

hot_rod

Copper tube boilers like a lot of flow, ideally piped primary secondary, or hydrosep. Some installation manuals had a bypass piped with them. I wonder with just that pex loop calling how it gets adequate flow?
If they start to lime up they make all sorts of weird noises also that transmit thru the copper tube.

Intplm.

@NotBob What you are describing sounds like one of your zones has air in it.
That zone needs to be purged of that air.
Have that zoned purged manually.
Also, ask a competent tech. to do some repiping of your boiler to help prevent this from continuing.
Without getting into much detail :
The expansion tank is upside down. Have never seen one on a boiler installed that way. Have it checked for proper air charge. Have it installed to the manufacturer's direction.
Replace or clean the air separator.
Pipe the boiler fill under the air separator at the point of no pressure change.
Ask your tech what he thinks.
It's hard to convey all that might be needed from here but this should give you a good start.

HVACNUT

If the circulator on the problem zone has an internal flow check, then along with a zone valve, the restriction through the loop can cause noise.
Also do you have well water? What's the floor standing extrol? FWIW, I've installed many expansion tanks facing up. Pressure is pressure. Hence the floor standing extrol.

Ironman

NotBob said:

Ironman said:

What’s the pressure on the boiler gauge when the system is cold?

Dead cold, don't know. With the gauge on the boiler at 130, it indicates about 8 psi. At 150 it's about 10psi. (The scale on that gauge is 0-90, and the pressure never seems to change much, so not sure how accurate I am with that.)

You should have a minimum of 12 psi cold pressure, more if you have a two or three story house. The pressure is too low and may be the cause of your problem.

You definitely have leaks on the system as indicate by the green corrosion.

It also appears that the fill line has been disconnected. The combination of these things could result in the boiler dry firing and possibly an explosion.

You need to get a COMPETENT HYDRONIC tech to look at it immediately. You have a potential bomb on you hands. A boiler explosion could level your house and kill any occupants.

mattmia2

I was trying to figure out where the feeder went, now that i look again, i guess the answer is nowhere. This makes cavitation a lot more likely especially depending on where the gauge is.

NotBob

Intplm. said:

@NotBob What you are describing sounds like one of your zones has air in it.
That zone needs to be purged of that air.
Have that zoned purged manually.
Also, ask a competent tech. to do some repiping of your boiler to help prevent this from continuing.
Without getting into much detail :
The expansion tank is upside down. Have never seen one on a boiler installed that way. Have it checked for proper air charge. Have it installed to the manufacturer's direction.
Replace or clean the air separator.
Pipe the boiler fill under the air separator at the point of no pressure change.
Ask your tech what he thinks.
It's hard to convey all that might be needed from here but this should give you a good start.

Thanks for the reply. I'm going to find a service tech. Our last one retired so I'll have to try someone new.

mattmia2

Whoever worked on that last should not work on it again.

NotBob

HVACNUT said:

If the circulator on the problem zone has an internal flow check, then along with a zone valve, the restriction through the loop can cause noise.

Also do you have well water? What's the floor standing extrol? FWIW, I've installed many expansion tanks facing up. Pressure is pressure. Hence the floor standing extrol.

Thanks for the input. We have city water. I don't know what the floor extrol is doing, other than its tee'd into the bottom of the air separator, like the other extrol. It does have a separate pressure gauge (reading 0) and a pressure regulator (?).
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NotBob

NotBob

NotBob

mattmia2 said:

Whoever worked on that last should not work on it again.

I understand the comment, but in fairness to him, we were buying the house and asked if it was serviceable for the time being. (We had plans to be here 3 years, and it's turning into 5+) He did a little something, and said it was OK, but he suggested we redo it all if we stayed. He suggested a getting rid of the boiler and redoing a lot of it with a special water heater as the source. He was actually very knowledgeable.

mattmia2

I was under the impression someone had disconnected the water feeder. I take that back. There is still something weird going on there, like it is fed from that big tank instead of a water line from the city so that tank needs to be filled from time to time.

Is it running antifreeze instead of straight water for some reason? If that tank is the source of feed water, someone should have given you instruction on how to make sure it didn't become empty.

mattmia2

The expansion tank should be pointing down to help it bleed air more easily, but it should still function.

NotBob

Ironman said:

NotBob said:

Ironman said:

What’s the pressure on the boiler gauge when the system is cold?

Dead cold, don't know. With the gauge on the boiler at 130, it indicates about 8 psi. At 150 it's about 10psi. (The scale on that gauge is 0-90, and the pressure never seems to change much, so not sure how accurate I am with that.)

You should have a minimum of 12 psi cold pressure, more if you have a two or three story house. The pressure is too low and may be the cause of your problem.

You definitely have leaks on the system as indicate by the green corrosion.

It also appears that the fill line has been disconnected. The combination of these things could result in the boiler dry firing and possibly an explosion.

You need to get a COMPETENT HYDRONIC tech to look at it immediately. You have a potential bomb on you hands. A boiler explosion could level your house and kill any occupants.

Thanks for the input. Yes, I've noticed the discoloration. It's never damp, and I think it's been like that since we owned the house. I assumed it was a legacy piece of pipe from a previous problem. Yes, it's becoming pretty clear we need to get someone in here.
Question: Where would the fill line be? Agreed, I don't see one. I assumed it was a closed system, and you wouldn't automatically add. If it leaked, it would sense a reduced level and shut down.

NotBob

mattmia2 said:

I was under the impression someone had disconnected the water feeder. I take that back. There is still something weird going on there, like it is fed from that big tank instead of a water line from the city so that tank needs to be filled from time to time.

Is it running antifreeze instead of straight water for some reason? If that tank is the source of feed water, someone should have given you instruction on how to make sure it didn't become empty.

Ah, that's possible but I never had a conversation with anyone about refilling that 2nd tank. There is a 5 gal antifreeze bucket in the utility closet (nearly empty). I'll attach a photo. So, yes, I assume it's running antifreeze.

mattmia2

Yup, that is antifreeze for a hydronic system. That big tank is filled with antifreeze and pressurized above system pressure, if the pressure in the system falls below the setpoint of the pressure reducing valve (the valve with the beige knob at the center near the bottom), the valve lets more fluid in to bring the system up to pressure. A very small amount of fluid loss through valve packings and such is normal, you likely have a bigger leak and have emptied that tank.

Once that tank is empty it won't keep the system at the proper pressure which can make the pump cavitate which can damage the pump or it may just not be able to remove air properly or both. It would be best not to run it until you can get it filled properly.

NotBob

mattmia2 said:

Yup, that is antifreeze for a hydronic system. That big tank is filled with antifreeze and pressurized above system pressure, if the pressure in the system falls below the setpoint of the pressure reducing valve (the valve with the beige knob at the center near the bottom), the valve lets more fluid in to bring the system up to pressure. A very small amount of fluid loss through valve packings and such is normal, you likely have a bigger leak and have emptied that tank.

Once that tank is empty it won't keep the system at the proper pressure which can make the pump cavitate which can damage the pump or it may just not be able to remove air properly or both. It would be best not to run it until you can get it filled properly.

OK, I understand. That makes sense. What I can do for sure is turn off the noisy loop. Its the 2nd floor, so elevated, and likely the one with the air in it. It gets some heated from other sections of the house, and we have a fireplace there.

Where the leak is, is a concern. I have not seen any indication of that.

Thanks! Much appreciated.

Zman

My guess is micro steam flashes in the boiler due to low pressure, low flow, scaling or all 3 combined. That boiler is very finicky at low flow. The manual calls for minimum flow rates and high flow piping configuration. Your installation certainly does not meet those requirements.

NotBob

Zman said:

My guess is micro steam flashes in the boiler due to low pressure, low flow, scaling or all 3 combined. That boiler is very finicky at low flow. The manual calls for minimum flow rates and high flow piping configuration. Your installation certainly does not meet those requirements.

Thanks for that info. I'll address that with the tech. About micro steam flashes... I was just asking myself today, what exactly is causing that noise? I really do not believe it's cavitation, and it immediately goes away when the boiler stops firing. Steam flashes makes sense. I had not put that together.

Fortunately with that one loop in the house disabled, it's quite normal/quiet now, so trying to line up a tech for Monday.

NotBob

For follow up...
I had the tech out today. His thought was that I had air in the system (making the noise), and that I was low pressure, maybe close to zero. He filled the system with antifreeze to about 20 PSI, and then everything was quiet. (That took about a gallon of antifreeze.) Afterward, he tried to bleed the baseboard radiators in the upper floor, but no air came out.

The theory there is that I WAS near zero pressure and the pipes were making noise/vibration because I was sort-of pulling a vacuum in the loop as the water headed back down the pipe to the boiler, then micro steam flashes may have been pulsing that.

He filled the reservoir pressure tank with the remainder of his 5 gal bucket, and then that came up to 8 PSI. We scheduled a followup visit for him to clean and flush the boiler, and then fill the reservoir up full so it's closer to 50 PSI.

So things are looking good. The house is fully warm. Thank you everyone for your advice.

mattmia2

When the pump is running it creates lower pressure on its inlet and higher pressure on the outlet. depending on where the gauge is it could have shown pressure but the suction side of the pump could have been near atmospheric pressure or below. that could cause either the water at the surface of the boiler to flash to steam or the water at the pump impeller to form water vapor bubbles. Keeping the system under pressure is important to keep the water a liquid. The glycol solution also has about 10-20% poorer heat capacity than plain water.