Oil fired Boiler doesn't heat water properly and creates banging noise

[Christian P]

Bought a home a few months ago and still struggling to set up my boiler correctly.

I have a SlantFin Liberty Oil fired cast iron boiler heating up two heating zones through baseboards and the water in the house.

After the first few weeks, I noticed two things:
1) Baseboards around the house were all cold (some of them were warm when I moved in)
2) Water when showering was hot only in the very beginning and began to drop after a short amount of time (1 min?) to become lukewarm.

Called a plumbing company and got the following results:

1) Heat not working because when boiler was replaced someone interchanged the return and supply pipes
2) Hot water issues are because the mixing valve is bad.

After the initial repair (minor repiping and replacement of mixing valve as suggested), I had my heat back but noticed significant noises in the baseboards and banging sounds at the boiler. The hot water issues persisted and at best I was able to take lukewarm showers if I didn't have the luck that the boiler was somehow miraculously jumping on while I was in the shower and provided hot water for a longer time.

Few weeks later, all the baseboards became cold again and it sounded like I had ocean waves coming through my baseboards. Called the same company and was told:

Heating system airbound. There is no air scoop, spyro vent or hy-vents on this system at all. System pump cavitation is due to air lock in the system. Added a second purge tee and drained on the return pipe to attempt to pump in the normal flow of direction as opposed to the supply when original boiler repair was done. Removed large amount of air.

After this repair, heat was back on and system was significantly less noisy in the baseboards. However, the boiler itself kept banging and had these strange cycles where it would jump on, shut off shortly after with a loud banging sound. I recorded that and posted it on youtube:

I'm not an expert but was hoping that somebody can make any sense out of the above. Maybe there are multiple things going on that are not interrelated.

I'm mostly interested why

a) I seem to not get consistently hot water and which parts of the boiler is regulating that
b) why the system creates the banging noise shown on the video and
c) whether air vents would avoid that the problem reoccurs that I have air trapped in the system or if I should expect that a plumbing company is regularly draining my system to take the air out.

I am also planning a coil cleaning as we have hard water where I live but heard that a dirty coil is more likely to cause uneven heat which seems to be not my problem.

Thanks everyone in advance for taking the time for reading and responding.

Christian

 

[Dana]

What is the system pressure, measured at the boiler? At low pressure (<10 psi usually) there can be "flash boil" or "kettling" where the (should-be) microscopic bubbles on the heat exchanger plates become fairly large, then collapse with a clap, clang, or bang as the flow moves the bubble off the hot cast iron and collapses suddenly. It is often accompanied by a noticeable sizzle sound of smaller bubbles forming & collapsing between the bigger bangs.

This is usually a pressure issue. Most systems work fine at 12-15 psi. But an older boiler with a lot of scale build up can sometimes have kettling issues even at those pressures. If you're going to change the system pressure bladder style expansion tanks need to be pre-charged to the new system pressure first.

Kettling runs pretty much constantly when the system is firing, but may slowly abate as system pressures rise. If the pressure is fine and it only happens when first firing up the noise is likely to be small explosions of unburnt fuel & air as the ignition lights it off. This can be due to either an extremely lean fuel/air mixture, or something off in the ignitor. Even if it eventually fires up and runs fine don't ignore this, since a full chimney full of unburnt fuel/air mixture packs a huge charge- big enough to damage your house. Most modern oil burners run the burner's blower for several seconds to pre-purge unburnt fuel/air from the boiler prior to letting the oil spray into the boiler to limit those risks. An oil burner tech (=not a plumber, though some plumbers get the training for this) should be the one doing burner adjustments & tune-ups.

Does the barometric damper on the flue open up a bit once the burner is firing? (It should- it might be sticking.) This isn't part of the banging, but the exhaust needs some amount of dilution from room air to avoid excessive condensation of acidic oil-combustion exhaust in the flue.

No heat is usually a low flow condition from a vapor lock with trapped air in a section of pipe on the loop, usually at a higher elevation on the system plumbing, since the bubbles will tend to collect and aggregate at the top. (You're more likely to see the second floor zones lacking heat than first floor zones). If the system pressure isn't high enough to keep the even the top of the system at positive pressure relative to the room pressure the system can even slowly take on air over time It's possible to purge air from the system without vents and air scoops, but it's a good idea to have at least one vent or air trap on the system designed to remove the bubbles as they pass by. Short of that, bleeder valves, particularly on the upper floor radiators can usually get you there once the major purging has been done by simply running water at a higher flow through the entire system (when it's tepid or cool, not when hot) to push out most of the air. Once the pressure is correct and the air is purged it can go for years without needing attention, even without vents or air scoops, but any time the system is opened up it has to be air purged. In systems with cast-iron baseboards/radiators and iron plumbing it's usually a good idea to flush the system annually to get rid of sludge build up in the boiler. If it's mostly copper or PEX once every 3-5 years is enough.

 

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[Christian P]

Hi Dana,

Thanks for taking the time to respond.

The system runs under a rather constant pressure of 20 psi. It sounds like that is perhaps too high?

Interestingly, that banging you see on the video doesn't happen when it fires up first but is almost its own cycle if that makes sense.
I hear that they system goes on and ends with a bang. Throughout that cycle the boiler itself doesn't jump on.
Maybe that cycle is the pre-purge you describe to take care of the unburnt fuel/air?

The barometric damper on the flue does open a bit and closes right away after each cycle.

Thanks for letting me know that it would indeed be a good idea to have at least one vent or air trap designed.

This morning I heard again this rushing through the pipes. It sounds like I sleep in the middle of the ocean. The question really becomes how does all the air get so easily in my system.

I was wondering if perhaps a leak somewhere in the pipes could cause the air build up in my system.

Thanks again..

Christian

 

[Fitter30]

Take a few pics of the boiler, 007 pump back side and piping. Whats the water your running?

 

[Christian P]

Pictures attached.

I'm running this 007e ECM High Efficiency Circulator (Taco) who some boiler experts seem to are skeptical about (not sure why).

Not sure on the question regarding water I'm running. It is a rather hard (high iron etc.) and I will schedule a coil cleaning which hasn't been done for a while.

 

[Fitter30]

Couple different problems with the piping. One is the piping of the expansion tank it can't be mounted on dead end piping it will trap air ( compression tank can be piped that way not a diaphragm that you have)
. Second the water make up line can't be on the discharge of the pump has to be on the suction side. Have to have a air scoop to get rid of the air in the system. For your domestic water is that city water running through the boiler heat exchanger? If so there hould be shut valves and drain valves on both line so vinegar can be pumped through to clean the heat exchanger.
https://www.google.com/url?q=https:...FjAAegQIChAB&usg=AOvVaw28pOPxF4mbRCSjxjBZvJwG
https://www.amtrol.com/product/air-elimination/
https://www.google.com/url?q=https:...FjABegQIARAB&usg=AOvVaw3vebMALcsuIO_yzHtbkELo
Look at page 5 top diagram for boiler piping

 

[Christian P]

Hi fitter30,

Thanks a lot for your insight.

I had no idea about the positioning of the expansion tank and it baffles me as I just had it replaced. I referred to the diagram you pointed me towards and it clearly confirms it: it can’t be mounted on a dead end piping.

I didn’t quite get the point on the water make up line. I understand the recommendation to get an air scoop to get rid of the air but what do I need to do to move the water make up line to the suction side. How can I tell whether my domestic water is running through the boiler heat exchanger?

 

[Fitter30]

City water feeds your hot water coil in the boiler. That valve with the three pipes , red cap is the mixing valve for your hot water. Problem with not enough hot water, varying temperature can because of the mixing valve and or a limed up city water side coil. Need a thermometer with shower on measure hot of boiler coil and mixing valve pipe to house see what is varying. Then turn on the kitchen sink with the shower measure temps. Are there any numbers on the coil in the boiler?

 

[Christian P]

Got it. Mixing valve was recently replaced as well. However, we do have a lot of iron and magnesium in our water so coil cleaning may indeed help to get the temperature to be more stable and stay hot. I am in process of getting an indirect water heater using the coil to get more reliable hot water. Also installing a water softener.

I will check regarding numbers on the coil tomorrow when I am back at the property (it is my second home).

Hope all of the above will help me to get all these issues solved. You helped me a huge step forward!

 

[Dana]

Hi Dana,

Thanks for taking the time to respond.

The system runs under a rather constant pressure of 20 psi. It sounds like that is perhaps too high?

Most 1-2 story homes with a boiler in the basement do just fine at 12psi. The primary hazard from running it 20psi is that if the expansion tank isn't properly charged the pressure can more easily spike over 30psi, the trip point of most pressure relieve valves installed on residential boilers. But if it's reading 20psi across a wide system temperature range either the tank is properly charged, or the pressure gauge is stuck (and not reading correctly). To sanity check the gauge, buy a cheap pressure gauge with a hose thread and find a purge valve or drain valve on the boiler or near-boiler plumbing and use a short garden hose to hook it up for a pressure test.

Interestingly, that banging you see on the video doesn't happen when it fires up first but is almost its own cycle if that makes sense.
I hear that they system goes on and ends with a bang. Throughout that cycle the boiler itself doesn't jump on.
Maybe that cycle is the pre-purge you describe to take care of the unburnt fuel/air?

I'm not sure what "...the boiler itself doesn't jump on..." means. On a pre-purge you'll hear the burner spinning, but no roar of burners firing. If you prop open the barometric damper a bit wider than normal with something you may be able to smell if fuel is being sprayed before the ignitor comes on. With the damper propped open you should be able to tell if the burner is running rich by the sooty-diesel type smell.

This morning I heard again this rushing through the pipes. It sounds like I sleep in the middle of the ocean. The question really becomes how does all the air get so easily in my system.

I was wondering if perhaps a leak somewhere in the pipes could cause the air build up in my system.

Thanks again..

Christian

If there's a leak in the system and it's running 20psi at the boiler it would be piddling or spraying water somewhere, not sucking air. If the system pressure is really <10 psi at the boiler, when the pump is running it's possible for the return side of the plumbing could be at negative pressure relative to the room's air pressure, pulling in air from connections that are still water tight due to surface tension, but not quite gas tight.

The rushing sound is almost certainly air bubbles in the system. If the system wasn't fully purged initially and there's no vent to separate out an purge bubbles the air will just stay in the system, since it has nowhere to go.

 

[Christian P]

Thanks Dana. I had the coil cleaned a few days ago which gives me now constantly running hot water.
A water softener system plus potential filters for iron will be installed next week.
I also ordered an indirect water heater to save some $$$ as I'm not in the house all the time.
Last but not least, I told the technician about the position of the expansion tank and that it shouldn't be installed at a dead end. He acknowledged that the installation of the tank is wrong. He will also install what he called spiral air vents to drain the air from the system.
He also pointed out that the zone controls are installed wrong (arrows pointing at each other).
I'm waiting to hear back what all that repiping and installation is going to cost me.

Thanks again for everyone helping me to trouble shoot!