Probe vs. Float low water cut off

georgede54 · October 2019

I’m looking to hire a contractor to install a new oil - fired steam boiler. I want it equipped with a low water cut-off. I believe there are two types: float or probe. Are there any other types I should consider? From what I have learned, I think I should go with the probe, but I’d like some input.

First of all, I have to be away from the house for weeks at a time and there is no one in the house to do the 7 – 10 day maintenance that I have read the float type requires. I have read that the probe type only requires maintenance on an annual basis. Even if the probe requires more than annual maintenance, it seems like my best, possibly my only, choice.

Second, I have read that adding water to the boiler causes oxidation, which in turn shortens the life of the boiler. So as the float requires more frequent adding of water, the probe would seem to be the better choice in terms of boiler life.

As I think about the second reason, I’m having a hard time finding a reason for anyone to install a float mechanism. The probe seems to be clearly the better choice, but there is a lot I don’t know.

I will be grateful for all comments.

Thanks.

George

Jamie Hall · October 2019

They both have their advantages -- and disadvantages. First, while the float type should be blown down somewhere around weekly to monthly, it isn't the end of the world if it isn't. Second, the float type is dead simple. It's a switch connected to a float. Float goes down, switch changes state, burner is shut off, depending on the feed system water is fed. No fancy electronics. No solid state circuits to fry.

The probe type, on the other hand, doesn't require much maintenance or attention, which may be a real advantage in some settings -- although leaving any boiler, steam or water, unwatched and unobserved for more than a few days at a time is a rather poor idea, in my opinion. Properly installed, they are reasonably reliable, as solid state circuits go. They can be fried by power surges, though, and completely defeated by incorrect installation.

All that said, again -- in my opinion -- a steam boiler should have two independent low water cutoffs, on independent tappings on the boiler (the float type is usually connected to the sight glass). So why not install one of each? And make the probe type the lower of the two, and manual reset, so if it does trip you know that you have a problem.

georgede54 · October 2019

Sounds like a good idea. Thanks.

EBEBRATT-Ed · October 2019

What @Jamie Hall said is good advise.

An automatic water feeder is a good idea if you are away often. A water meter installed with it is a good idea to monitor usage. It's better if you add water yourself and check the boiler occasionally........but if you away the feeder provides back up

Steamhead · October 2019

Probes, all the way.

What model boiler are you considering?

Where are you located?

mikeg2015 · October 2019

I had a probe and needed the tapping for a aquastat so went back to a float. I trust it just a bit more for some reason. Although a clot sticking is most likely than a probe failure.

georgede54 · October 2019

Thanks for all the comments. Here are my responses.
1) I'm planning to add water whenever I'm around, but I'm still wondering about the cold water in a hot boiler problem. Are there certain times I can't put water in?
2) I'm located in New Rochelle, NY, which is slightly above the Bronx.
3) I'm not going to think about boiler models until after I have figured out how many BTUs the boiler should crank out.
4) Mikeg said he had a float but needed the tapping for a aquastat so he went back to a float. I'm not completely clear on what that means and I'm wondering whether that's a problem I could be running into.

Thanks again.

George

georgede54 · October 2019

Mikeg had a probe - sorry.

Jamie Hall · October 2019

On your Number 1 -- unhelpfully, it depends... if you are not adding much -- half a gallon or so -- and are adding it through the wet return, it really doesn't matter much. On the other hand if you are adding several gallons at a whack through a tapping directly into the boiler, best to wait until the boiler has been cooling for a few hours if you can.

On number 4 -- Depends a lot on what tappings are available on the boiler, and what they are used for. Many boilers have a tapping which is rather specifically meant for a probe type low water cutoff -- it should be noted in the installation manual. Most if not all boilers will have two tappings meant for the sight glass -- one quite near the top, and one lower, below the operating water level. Those two are commonly used for a float type low water cutoff, which needs two tappings spanning the operating water level. There may well be other tappings in the boiler -- indeed, there should be. On a boiler which is already installed, they may well be hidden under the cosmetic shroud. Your boiler installation manual should note them all -- and often, helpfully, suggest what they might be used for.

georgede54 · October 2019

Thanks for all the help. I got a lot to learn and must keep plugging away at it.

georgede54 · October 2019

Could someone please give me an explanation of what a "tapping" is or does, how many of them should be on a new boiler, and where they should be located. Thanks!

Jamie Hall · October 2019

A tapping... as we are using it in this thread, is any hole in the boiler casting which has been threaded (tapped) to take a fitting or pipe. How many of them should be on a new boiler? Depends on the boiler! Likewise, where they are located.

georgede54 · October 2019

Thanks!

ethicalpaul · October 2019

I bought my boiler as a package and it included a LWCO already installed. I can't imagine that a competitive installer wouldn't want it to come like that to avoid ordering/stocking/installing them but what do I know?

And I imagine it's in the boiler manufacturer's best interest to install a decent one that's not going to end up destroying their boiler. Not that boiler manufacturers don't do crazy things sometimes (like give you a pressuretrol set to 10psi on a pigtail that can't be easily disassembled for annual cleaning, but I digress)

PS: my homeowner opinion is that I don't want any part of dealing with a float-type LWCO

Fred · October 2019

@ethicalpaul said: PS: my homeowner opinion is that I don't want any part of dealing with a float-type LWCO
Paul, I really think it's whatever you get use to. Both the probe type and the float type are very reliable (I would avoid the Cyclegard like the plague because of its shutdown feature). I have the Float type and I think nothing about blowing it down periodically. I often wonder where the crud goes with the probe type; just settles on the bottom of the boiler, I guess, and if you have to drain some water out of the drain valve, periodically, it is not much different than the attention given a float type LWCO. In my case, the boiler lacks a properly placed tapping to place a probe type LWCO and the float type mounts right off of the sight glass fitting. There are pros and cons to both styles. JMHO

georgede54 · October 2019

Thanks. You seem to know a lot more than I do. Someone suggested installing both types. Any thoughts on that idea? As I mentioned above, I have to be away for long periods of time, with no one to check up on it. Finally, someone said the probe type could get fried by power surges, which is leading me to deduce they operate on electricity. Might it help to install a surge protector? Thanks again.

Fred · October 2019

georgede54 said:
Thanks. You seem to know a lot more than I do. Someone suggested installing both types. Any thoughts on that idea? As I mentioned above, I have to be away for long periods of time, with no one to check up on it. Finally, someone said the probe type could get fried by power surges, which is leading me to deduce they operate on electricity. Might it help to install a surge protector? Thanks again.

There certainly is no issue with installing two LWCO's. It provides another level of protection. The probe type is powered by electric, either 24V or 110V depending on your system. We don't see or hear much about power surges frying them but I suppose anything is possible, given the right set of circumstances. I would check before I added a surge protector to your safety system. Some surge protectors also provide some level of power back-up and should one of your safety devices trip, it trips for a reason and you want the power shut down immediately. Safety is a necessity but, like everything else, don't over think it. The boiler manufacturer's guidelines are usually sufficient.

georgede54 · October 2019

I have just posted the information and pictures necessary to compute the EDRs for my upstairs radiators in a new discussion titled "Computing the EDRs of My House Radiators for a New Oil-fired Steam Boiler." If you want to take a look and run the numbers, I'd appreciate your efforts. Thanks.

KC_Jones · October 2019

My old boiler was 32 years old, had the original probe LWCO still functioning perfectly and to my knowledge it never had any maintenance, ever.

georgede54 · November 2019

Something caused my boiler to crack after 14 or 15 years, and I am trying to figure out what it may have been, so I can get 30 years out of the next one.

Fred · November 2019

georgede54 said:
Something caused my boiler to crack after 14 or 15 years, and I am trying to figure out what it may have been, so I can get 30 years out of the next one.

Unfortunately many, if not most of the boilers produced today have about a 15 year life. Some only 10 or so years. All in the name of making them more "energy efficient" and reducing manufacturing/materials cost.

georgede54 · November 2019

So, you are suggesting that nothing may have gone wrong with the installation or maintenance of my boiler. Do the manufactures tell us how long the boilers are supposed to last? Thanks.

SlamDunk · November 2019

There are many posts on this board that say water quality and/or manufacturing quality play a role in how long a boiler will last.

If it puts your mind at ease, mine is 10 y.o. but I'm knocking on wood as I type this!

Fred · November 2019

@georgede54 , most cast iron boilers are warranted by the manufacturer for 10 years. After that all bets are off. Installation, water quality, excessive make-up water due to leaks elsewhere in the system, lack of proper maintenance all affect the life of a boiler. Newer boilers seem to have an average of about a 15 year life, if you're lucky.

georgede54 · November 2019

Thanks. You have put my mind at ease. Maybe nothing did go wrong with the installation or maintenance, so I should get on with having a new one put in and not worry about, or try to figure out, what went wrong with the old one.

SlamDunk · November 2019

If you know what you need size wise, and what it should look like post install, 3/4's of your job is done. Only thing left to do is to find the right person to do it.

georgede54 · November 2019

I agree with your three-part analysis.

I'm 80% sure that I know what size I need. I posted information and pictures of my radiators on a different discussion titled, "Computing the EDRs of my house radiators . . . " Someone got a chance to look at the EDR of my upstairs radiators and his computations agreed with mine. I then posted information and figures on the downstairs radiators (I had to get into the tenant apartment), but no one has gotten a chance to check over my work. Thus, I'm only 80% sure of the boiler size I need.

Now I have turned to finding out what it should look like post install. I figure the more I know of that the better chance I have of finding the right person to do the job.

Thanks.

SlamDunk · November 2019

down load a manual for the boiler you wish to have, it will have a near piping diagram.

georgede54 · November 2019

Great idea! Thanks.

Probe vs. Float low water cut off

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