knocking in boiler

nuge0013

I've had 3 HVAC companies come out to look at a knocking noise that can be heard in this video:
https://photos.app.goo.gl/w3KbKdkZbqrtsKo66

All 3 companies said that even though this Weil-McLain boiler is very old, it still had life left and was in pretty good shape for its age. All estimates to fix it involved a new fill valve, backflow preventer, and expansion tank, as well as a good cleaning. We hired the neighborhood favorite to do those things, plus he put in a new pressure relief valve. The noise is still there, although the knocks are a little slower than what is heard in the video, and it happens for less time overall and less frequently during the heating cycle. So there was some improvement. The professional says it is air trapped in the system, plus "normal" sounds of metal expanding when it heats. However, it echoes through the pipes up two floors and is enough to wake me in the morning. This has not happened previously in my 10 years of living here, so to me is not "normal" for this boiler to be woken by it. I've bled the radiators and only get water, no air. Also, the pressure reads about 28 psi at its hottest point of the cycle, which seems high. I'm looking for ideas on what this noise is and what my next step should be with this professional or some other. Thanks.

Jamie Hall

Did anyone dexcale the water side of the boiler? Or just clean the fire side. Sounds to me like "kettling" -- aptly named, since it sounds like a kettle coming up to a boil on the stove. Try running a descaling compound through the water side of the boiler -- well, drain it, fill it with the solution, let it sit for a bit, then thoroughly flush it a few times, then refill.

The high pressure isn't right -- what does the pressure read when the system is cold?

leonz

Yup, its kettling and needs to be cleaned internally with a descaling compound and the fire side should be serviced and cleaned as well.

EdTheHeaterMan

It could be that Ty D Bowl man got stuck in the wrong appliance. What color is the boiler water?

nuge0013

Thanks for the replies! Kettling is not something any of the 3 companies mentioned, but reading about it now, that does sound like it. There's also a faint whistling at times when I get close to the exhaust stack, but not consistent.

They did clean the fire side, but I don't know if anything was done with descaling compound. Is that something a reasonably handy DIYer can do?

Pressure reads about 19 psi when cold.

I don't know what color the water is. It looks clear when it comes out of the radiators I tried to bleed. They had to empty water out of the whole system and all radiators to replace valves and expansion tank, so it's got all new water now.

hot_rod

A thorough cleaning involves a coil cleaner and pressure wash on the coils, and running an acid based cleaner inside the coils


A mirror and flashlight from below is a good way to judge the condition of the coils.

You pretty much have  to take  the HX out of the enclosure to do a deep clean

nuge0013

Sounds like the descaling is a job for the professional. If he responds to me about the high pressure (I alerted him to this yesterday), I can have him do it. It sucks to pay even more on this to still be fixing the original problem. But I want this noise to stop. How do I as the homeowner suggest that the problem is kettling and ask him to descale without insulting him, given that he is the one who is the professional here?

Can kettling explain the high pressure situation?

Jamie Hall

Try referring you man or woman to this thread...

No, the kettling and the pressure aren't related. And 19 psi cold is too high as well. It may be that your pressure reducing valve isn't set correctly, or is set too high.

Larry Weingarten

Hi, I agree with @Jamie Hall that the noise sounds like there is sediment slowing heat transfer and causing boiling. This is pretty common in domestic tank-type water heaters and is always fixed by removing the sediment. The mechanism is that heat transfer is slowed by the sediment. Water in the sediment flashes to steam, and then when the steam hits cooler water, it collapses suddenly creating the sounds you hear. A sure test for this is to reduce pressure in the boiler when it's making the noise. If that increases the noise, it is a confirmation. There has been a citric acid descaler made for water heaters, MagErad, but I'm not sure it's the right thing for a true boiler.

Yours, Larry

hot_rod

19 psi is not a problem as long as the expansion tank was pre charged to 19 psi.
12-15 psi is adequate for most residential 3 story or less.

If pressure rises from 19- 28 it sounds like the tank is under charged, has a volume or water in it reducing the acceptance.
New expansion tanks should always have the pre charge tested when you take it out of the box.

Sometimes installers or troubleshooters bump static fill pressure for problematic air problems, maybe an attempt to quiet it down?

Hercules Sizzle is a good product, easy to find for deliming boilers. Follow the mixing instructions carefully when blending acid.

nuge0013

I have a professional here who is willing to try this with Sentinel X300. Will that do the job, or does it not descale? Hard to tell from the bottle, which only mentions removal of "sludge"

hot_rod

it depends on what the build up inside is. That product is a strong detergent, good for most sludge cleaning.

If it has mineral build up from hard water, I've found that an acid based cleaner works best. this was the go to for cleaning DHW copper tube boilers as they got the mineral build up from the incoming water.

This is a handy product for plumbers as it could be used for drain cleaning and many other purposes.

WMno57

Probably kettling from scale but ...
I see a red Bell & Gosset circulator (pump) in your video. Those have a coupler between the motor and impeller that makes noise when it starts to fail. The coupler can be replaced. You could put your hand on the top of the motor to see if you feel vibrations.

nuge0013

Thanks for the replies! WMno57, pump does seem okay. Plus, no noise while it's just circulating. It's only when the boiler is actively firing.

Are any of you in Maryland? Ha, ha. Why does it seem nobody here has heard of this issue?

Because the professional who was here with the X300 thought it would work and was thus far the only person willing to try it, we went for it. It was a time-sensitive decision. Unfortunately, I haven't noticed any improvement so far. But maybe it has to be drained and flushed before you can really assess? He'll do that next week.

I don't think I'm going to be able to convince him to do another round of draining, filling, etc. with a true acid-based descaler. I might be able to convince him to help me put in some Sentinel X200 Noise Reducer at the final fill next week. It's made to be left in the system, I guess? And the regular (non-Sizzle) Hercules Boiler Cleaner also says it can be left in. Is that right? Which one of those would be my best bet for solving the problem, and the least damaging to my Weil-McLain boiler over time without a drain and flush?

If I decide to just live with the noise, is that dangerous in any way?

WMno57

Are any of you in Maryland?

Yes.
https://heatinghelp.com/find-a-contractor/state/MD/
@Steamhead is an active Wallie here. I'm sure he could resolve this for you. Here is his listing:
https://heatinghelp.com/find-a-contractor/detail/all-steamed-up-inc/

hot_rod

nuge0013 said:

Thanks for the replies! WMno57, pump does seem okay. Plus, no noise while it's just circulating. It's only when the boiler is actively firing.

Are any of you in Maryland? Ha, ha. Why does it seem nobody here has heard of this issue?

Because the professional who was here with the X300 thought it would work and was thus far the only person willing to try it, we went for it. It was a time-sensitive decision. Unfortunately, I haven't noticed any improvement so far. But maybe it has to be drained and flushed before you can really assess? He'll do that next week.

I don't think I'm going to be able to convince him to do another round of draining, filling, etc. with a true acid-based descaler. I might be able to convince him to help me put in some Sentinel X200 Noise Reducer at the final fill next week. It's made to be left in the system, I guess? And the regular (non-Sizzle) Hercules Boiler Cleaner also says it can be left in. Is that right? Which one of those would be my best bet for solving the problem, and the least damaging to my Weil-McLain boiler over time without a drain and flush?

If I decide to just live with the noise, is that dangerous in any way?

Some of the cleaners are intended to be left in the system. They dissolve the scale, remove it from the metal surfaces and keep it in suspension, called chelates I think.
They turn color so you know that the ph is safe. You can get Ph up or Ph down adders also to get to a safe level after an acid cleaning.
We used a product from Mile High Chemical in Denver for copper tube "quietiers". Back when copper tube boilers were the most common radiant boiler. I don't know if they are still around. Pump it in, and within an hour or two all the noise went away, very effective. Could be used in cast boilers also.

The descalers used in tankless water heaters would be safe for the multi-metal hydronics also.

If it is a limescale deposit, it will hamper the heat transfer, eventually the metal over heats and breaks down. It can also cause a boiler to hit high limit and trip out. Just depends on the layer of build up. I profess efficiency drops as any heat transfer surface starts to get a layer of scale build up.

Percolation is the noise @Larry Weingarten described, you heat the sediment, the sediment heats the water. A common sound in old, or new tank type water heaters when they start to accumulate a scale build up.