Boilers - Steam and Hot Water Systems - boiler maintainence

I was recently reading through some of the threads in this area to see if I could help with any issues. I had noticed in one thread, that boiler maintainence got brought up. I had already learned that you DO NOT drain a boiler unless you have to. I have read the manual on my weil mcclain cga-4, but it did not mention a lot of specific information as for maintainence. I do believe that I had read somewhere that there are chemicals used to flush out boiler piping? Does anyone have more info on this, and more info on routine maintainence on boilers that is more specific than what my manual states?

Well,

Draining the boiler will remove any crud that builds up for sure, but since it's a sealed system there really should not be any crud building in the first place.

Draining the boiler means you need to fill it again, which means gallons and gallons of fresh water. And what else is in the water ?

Well, oxygen is in the water, and oxygen and ferrous metals is good or bad ? BAD.

One needs to make sure the burners are clean, the heat exchanger is clean. Inspect the venting for signs of flue gas condensation, IE root.

Check expansion tank, or air cushion tank for proper fill.
Make sure the fill pressure reg works.
Some people say to test the PRV, but I never touch them as they usually leak after letting water out.

And really I find it important to ensure there are no minute water leaks anywhere in the system. A small leak can bring in hundreds of gallons of fresh water, and of course oxygen. This will root the boiler, and the system pipework and rads in time.

Draining the boiler means you need to fill it again, which means gallons and gallons of fresh water. And what else is in the water ?

Well, oxygen is in the water, and oxygen and ferrous metals is good or bad ? BAD.


yes, there is definately oxygen in the water, which will cause corrosion in the pipes. As for any types of contaminants, there should be very few. When I first moved into my house, I installed a whole home filter that filters down to 5 microns. The water supply to the boiler goes through this filter.

Make sure the fill pressure reg works.
Some people say to test the PRV, but I never touch them as they usually leak after letting water out.

I would definately agree with this. I actually tested the pressure relief, and as you mentioned, yes, now it will leak out the occasional few drops of water. Finally, as for chemicals to flush out the system, do you know anything about this?

Finally, as for chemicals to flush out the system, do you know anything about this?Should not be necessary for a closed system - I wouldn't do it.

If your system is steel pipe and a cast-iron boiler, the water will look like ink if you drain a sample. That is not a problem. You could flush it until the cows come home, and in a short while it would look like ink again.

Sometimes newly installed hot-water or steam systems were initially flushed with chemicals to remove oil, grease, and mill scale. That was a one-shot deal.

Don't think of a closed hot-water system like your car's cooling system. Cars are not really a closed system - every time the engine heats up, water is discharged to an open expansion tank and then sucked back in when the engine cools. This injects oxygen into the car's coolant. Car cooling systems use inhibitors that aren't required for closed hot-water systems.

Cleaning out the heat exchanger part of the boiler is very important. Especially if oil fired you can get a significant layer of carbon on the heat transfer surfaces (where much of the fire's heat goes into the boiler water). These are pin fins on my old boiler. Special brushes are sold at plumbing supply houses for this (dirty) task. If your oil burner has been 'tuned' to run rich, these important areas can really get clogged with carbon over a single season and make for a very inefficient boiler. Why would someone tune it rich? Hmmm.. to sell more oil perhaps...

You could drain out a sample bit of the water and have it analyzed for ph balance and other properties.

@MikeSpeed.. I wonder if using an expansion tank for a closed system in automotive cooling would keep system rot quite a bit lower ??
Also.. I wonder if thats why most of my wirsbo lines went noticeably darker than 'new'.. my bud the pipefitter did my hardlines with some sched80 he had on hand.

Well, my boiler is fired by natural gas. Where about is the heat exchanger located? what does it look like? Finally, I have sampled the water several times while draining off the boiler to work on it. (It was plumbed in backwards and all screwed up when I first bought the house.) The water comes out of the drain "clear", but once it settles into a container, yes it does turn rather black. Why is this?

Black, eh? hmmmm...

I do know that 'stuff' can get dissolved in water and appear clear, but then when exposed to oxygen, it oxidizes.

My well water is a perfect example... if I take a sample ahead of the iron removal and softener, it will appear clear for a period of time, but then slowly turn a nice disgusting orange color. The water from the ground is relatively oxygen free... so the iron remains 'clear' and unoxidized (rust). Once the air hits the water, it oxidizes.

Boiler water is relatively oxygen free... so there could be 'stuff' dissolved in it that isn't oxidized. Same deal when the air hits it.

But what would oxidize BLACK? Sulfates? and where would the substance be coming from? leaching out of the cast iron?

Well, my boiler is fired by natural gas. Where about is the heat exchanger located? what does it look like? Finally, I have sampled the water several times while draining off the boiler to work on it. (It was plumbed in backwards and all screwed up when I first bought the house.) The water comes out of the drain "clear", but once it settles into a container, yes it does turn rather black. Why is this?When you say it was plumbed in backwards, what exactly do you mean?

Maintenance procedures are here: http://www.weil-mclain.com/downloads/literature/cga/cgaboilermanual.pdf

A gas-fired boiler shouldn't need to be cleaned on a routine basis - Unless the burner air is so far out of adjustment that there is soot being formed. You can check inside the flue area for soot, but it would be unusual.

The black color of the circulating water is normal and involves a reaction of the iron. I don't know the exact chemical reaction, but it's not rust or corrosion in the usual sense. I asked John Siegenthaler this very question, and he confirmed that the black color is normal, but he couldn't recall the chemical reaction other than that it involved the iron. Not to worry.

Copper pipe is now much more commonly used than black pipe, and maybe the ink factory doesn't operate nearly as much as with a steel pipe system?

Some people also report that their water has a foul odor. I haven't noticed that so much.

When you say it was plumbed in backwards, what exactly do you mean?

It was a mess... among other things, the circ pump was pulling from the bottom and the return was going back to the supply!

See this thread:

http://forum.doityourself.com/boilers-steam-hot-water-systems/403892-boiler-noise-expansion-tank-issues.html

I've done a little googling, and have a probable explanation for the black boiler water.

Pure water (no disolved oxygen or other impurities) can react directly with iron to form magnetite, which is black in color. The reaction in promoted by temperature. Here is the reaction:


3Fe + 4H2O = Fe3O4 + 4H2

Magnetite is an oxide of iron, but unlike ordinary rust (Fe2O3), its formula is Fe3O4. Rust is usually red while magnetite is black.

Now, look again at the chemical equation for forming magnetite. The iron is readily available in steel pipe and in a cast iron boiler. But what happens to the hydrogen gas on the right-hand-side of the equation? My guess is that it disolves in the water and scavenges any oxygen in the water, forming H2O again (good).

Magnetite can adhere to steel and iron surfaces, forming a protective layer (good). But for our typical low-temp heating boilers, it seems that much of it winds up in the circulating water, causing the black-ink color.

I don't know whether the magnetite actually disolves in the circulating water or if it is sort of a pigment. But either way, it seems to cause no problem.

I can forgive John Siegenthaler for not recalling the exact chemical reaction. Tomorrow, I won't either.

According to my Burnham manual, if the water is grey or black there is excessive oxygen on the system.

Ok, so if too much O2 promotes the magnetite formation, it's probably going to magnetite rather than normal rust because of the temperature then... my guess... or, perhaps it goes to rust first, and then 'picks up' the extra molecules when it's heated... in other words, first to rust, then to magnetite.

I think that 'protective coating' is also called 'passivation'.

The 'stinky' water could be caused by anerobic bacteria that will survive at the higher temps... this is the reason that some ppl have stinky water from their water heaters... sulfate reducing bacteria... harmless, except when they pass gas...

correct! then the water does not smell so nice!