I have a Weil-Mclain boiler for a hot water heating system. Over the last two years, the water softener has failed, and a recent hydronic loop purge and recharge left the boiler and heating loop full of hard water. All of a sudden, the boiler began making popping and clunking noises during the burner cycle. I assume this is due to calcium deposits in the heat exchanger from the hard water.
What remedies are available for this problem? Weil-Mclain recommends acid cleaning of the boiler as detailed in one of their technical bulletins.
Replies
I suspect
you need to flush the unit with vinegar or another very mild acid.. Usually involves connecting a small pump to the boiler's inlet and a short piece of hose to the outlet, filling a bucket or a small trash can with the acid, and then pumping acid through the unit and into the bucket, over and over and over.
Obviously this means taking the boiler out of the heating loop, and may be simple or not depending on the types of connections already made.
I would probably get Weil-Mclain on the phone and double check your plans with them.
Cleaning scale
Thanks David. I think that is basically what needs to be done. Weil-Mclain recommended an acid soak method with 6% muratic acid. I might check back with them after reading their bulletin on the acid cleaning. Getting the boiler isolated, mixing acid, keeping the acid off of citical areas, rinsing, testing PH-- all of that seems like a big job. I would have to wait until summer so I could allow enough time for the work.
A plumbing contractor here refuses to do this acid wash because they don't trust the recommendation from Weil-Mclain. The contractor says they have an injector tool that they can use to inject some type of compound into the boiler through the drain valve. They leave the boiler fully connected to the loop and they just leave the compound in the system. They say the treatment sometimes quiets the boiler down permanently, but sometimes the effect only lasts for about a month, and then the sound comes back. But the contractor cannot explain exactly what this treatment does. If it quiets the boiler by disolving the scale, why would the sould come back in a month?
If I research this topic, I find lots of very technical methods of controlling water quality in commercial boilers, but not for residential boilers. It just seems like there should be an injector system on a boiler that would be used for adding compounds that would perfectly condition the water. After all, it is only maybe 5-10 gallons in a captive system like an engine cooling system.
I find it a little hard to believe that one charge of hard water would cause extensive scaling. Unless you were feeding in new water continuously (eg, due to a leak) then the total amount of hardness minerals introduced is not that great.
kd
is the air bled out of the system?
I am not sure about the air issue. Would air in the system cause scale buildup in the heat exchanger? I used to bleed a tiny amount of air off with a small device on top of the expansion tank. It was never really clear to me whether it was fully bled or why there was always a little bit of air available. My understanding is that evey new water charge releases oxygen in the loop, so there is a ongoing source of gas generation. In any case, I have not bothered to use that little bleeder for the last couple years because the last time I tried it, it did not re-seat for a while. It looks like a tire valve.
I usually end up recharging the system for one reason or another at least every 1.5 years or more often. It is a purge system, so the recharge is full flow into the system, through the loops, and out a drain hose. Then I slowly close the drain and the feed, but let the feed stay ahead of the drain, so the pressure builds to around 25 lbs., and then close both valves. So it seems like it would be free of air with that kind of fill process.
I think I have completely lost soft water sometime in the last 2-3 years, so that might have had hard water in the loop for that long. It is 28,000 grains hard. I don't think there are any leaks that are continuously feeding water into the system. That would raise the pressure and open the relief valve. The Weil-Mclain guy said it sounded like somebody got a slug of hard water into the boiler recently. When it fires up, it sounds like somebody playing bongos. And it is coming right from the boiler.
I've never heard of calcium deposits causing clunking noises in a boiler system. I had a Weil-Mclain boiler that was 20 years old running with just hard tap water in it and never had the problem. You're sure the system is properly purged?
Hard water will definitely cause such noises in water heaters, but of course water heaters are constantly being exposed to "fresh" hard water.
I am going to check into it further with Weil-Mclain and some other contractors. I does seem rather unlikely that the limited amount of water in the closed system could offer enough calcium to build significant scale in the boiler. Regarding air in the system, I will look into that closely. I know that the circulating loop is capable of producing lots of different sounds that seem unexplainable.
When I inquired with Weil-Mclain, I talked to somebody who seemed to be their top technical guy the contractor inquiry section. When I described the problem, he immediately referred to it as the teapot sound, and said it was calcium/lime buildup from hard water.
This boiler has been in service for 17 years, so maybe another possibility is that the soft water was not soft enough for a more prolonged period of time. I just replaced the water softener. That is a whole other issue. I need to set up my own water testing lab in the basement.
Shouldn't be scale
A hot water heating system is supposed to be a closed system. Even relatively hard water will not create significant scale because once the system is filled it is closed off. There is not enough hardness minerals in a system fill to cause any significant scale. Unless there is a significant leak one doesn't need to add additional water (and hardness minerals) to the system. You didn't mention a system leak so there shouldn't be any scale, as DanH has already suggested.
Maybe you should concentrate on the expansion tank. There needs to be a certain amount of air in the expansion tank. The air allows the water to expand as it is heated. Otherwise the system will experience significant stress as the water is heated which can cause all sorts of bad noises. You state that you have been regularly bleeding air from the expansion tank. Um, yikes! With no or minimal air left in the expansion tank your system is being severely stressed when heated. If your expansion tank has a diaphram, you may also have blown a hole in it since you removed all air. You may now need a new expansion tank. Usually the tank is marked with the recommended air pressure.
Many years have passed since your post, but I would like to share information. Dealing with boiler scale buildup can be a real hassle. In my experience, using a descaling solution specifically designed for boilers can be effective.