Steam boiler and indirect hot water tank in the summer

If the indirect is 15 years old there could be some sludge around the sensing well of the aqua stat in the indirect. You or your plumber would have to drain the indirect and take the well out and flush the tank.

The other possibility is someone turned the aqua stat in the indirect up too high, but I would think you would notice very hot water if this was the case. Normal setting might be 120 ish.

If the aquastat on the boiler is set to 160°, the steam pipes might be cold, but the boiler water should be between 160°-140°. If you raise the temperature on the indirect, the supply water from the boiler should be at least 140° right away when the circulator starts.

this periodic draining is causing the sludge. The fresh water corrodes the boiler making more of it. You can nearly eliminate creation of new sludge but it requires the use of ph boosting additive such as 8-way.

it can be tricky to implement in an old boiler, but for sure stop periodic draining

@ethicalpaul and I have always been friendly and have some people in common but we part company on this topic. My experience is that indirects and steam boilers are misapplied as often as they are well applied.
Why I like them? The combustion efficiency of the boiler is much better than that of a standard gas water heater and, while the standby losses of the boiler are somewhat abysmal, the standby losses of the indirect are next to nothing. Even if those factors would amount to a wash, I still prefer the indirect route so long as it is of stainless steel construction (lifetime warranty) and prefer to have a single heat source and eliminating a second carbon monoxide maker.
Also, if Burnham has done nothing else, they have done a great service to indirect water heater installers across the universe by cutting the dedicated tappings into their end sections for the supply water and aquastat well. Your Burnham Independence series unit is as good as it gets for matching the two pieces together.

Adding this….I love Weil-McLain but they've always been light on tappings, making a real of task of adding a second LWCO or a hydronic/DHW loop. I know. They've still got the optional gas-steam-tankless coil option but it's a very expensive way to make it work.

Get rid of the sludge. Occasional drainings it certainly not helping. Dump a whole bunch of eight way into the boiler. Run the boiler until it starts to steam. Then stop right away. You want to keep the boiler hot for 30 to 60 minutes. Not a bad idea to turn it back on every few minutes. To keep it hot. You don't want it to steam much. Afterwards, drain fill drain fill drain fill.… You will see coffee and chocolate milk coming out. Once it comes clear, run the boiler for a good 20 to 30 minutes.

Inspect the wires to the boiler's aquastat, if they are erroneously touching that would prevent the boiler's aquastat from shutting off the burner when the water temp reaches 160 degrees.

Do you have a multi-meter ?

You could test the boiler's aquastat. Using the space heat thermostat to control the boiler, as the water warms up but before steam is generated the aquastat's switch should open consistently with each time the boiler is warmed up.

If the aquastat's switch has continuity when the boiler is producing steam the aquastat is defective.

You mentioned the pipes were at the normal and expected temperature this morning. As most everyone is pointing towards, it seems the runaway heat is happening on a hot water call. Overheating the boiler.

Technically, the aquastat should be killing the burner when the aquastat sees 140. But evidently, that’s not happening. You might have two problems on your hand.

You know your house, and how much hot water is being used, your concerns are valid

It’s a little bit odd that your problem went from nothing to something in one season. Not shocking, but just note worthy

This is a little bit long, but if you really want to understand how this process works:

We did a steam boiler swap last week. The existing super stor indirect water heater remained. We had trouble at the end of the day getting circulation to flow through the water heater’s coil. It was late in the day, I suspect the circulator took a nap or the flow check was sticking. I could hear the old Taco 007 making a wurring sound (trying to do its job), so my hunch was flow check issue.

This is getting a little bit in the weeds, but we could only force Water into the “open boiler“ with our hose. Also had to push in the opposing direction of the flow check (that’s how it was piped). I opened the flow check, but it was super sticky (very difficult to turn the spindle and it was making a rough creaking sound)—-my presumption was the flow check was hampering flow during our purge effort. After all, the flow check is iron, and, the steam system is open to the atmosphere.

The next morning, I cut out the flow check. But to my surprise, it was clanking when I shook it up and down. I wasn’t about to put it back in, I tossed in a new iron flow check. I also cut in another ball valve and boiler drain: a way to hook up street pressure to purge the coil with “full street pressure”. Now- I don’t have to purge “against” the flow check. Got it all back together and circulation was restored, back to normal. No more wurring sounds from the circulator. The “return” heater immediately.

That’s a long way to say, I’m wondering if plumber effectively purged the coil. When was that last 0010 installed ?

He’s either purging into the “open boiler” or he’s pressurizing against an opposing ball valve. The latter option is tremendously more effective. Many indirects water heaters need a good amount of flow to fully purge the coil.

During the hot water production call, close the ball valve on the hot water loop, do you hear any velocity ? I lovingly call this the “swoosh test”. If you don’t hear anything, that’s not good, you’re not flowing (or, you’re flowing a minimal amount)

if my theory is incorrect, and you are flowing 100%, my next theory would be the wye strainer is gooped.

and your 140 setting may not be working well. Try turning it down to 120 or even 100. The aquastat may be losing its gas. You will have to experiment- once the boiler is heated up it will take hours for it to cool down and try again.

Hope this helps

op/ed- for decades I was more pro-indirect on steam. For the reasons that John pointed out. Then, I think I did a job or two where the tappings on the block were unfavorable. It managed to sway my thinking about indirect/steam. Then it occurred to me- not all boilers have lots of taps. At this juncture in my career, I am 50-50. I am fine with putting an indirect on a boiler, I am fine with doing something separate. If need be, I’ll get a coin out and flip it.

If I bought some cool older home with steam, knowing me, I would probably have an indirect set up. And I would probably have a second water heater sitting to the right or the left, just because I like redundancy. Money is literally no object when it comes to mechanical stuff in my own.

I mean the ball valve that interrupts the flow of circulation between the boiler and the water heaters heat exchanger.

three years ago, OK I guess that theory does not apply.

Still seems like you might have two issues going- perplexing.

Bob yes ok it would be just as the valve gets closed (about 80 to 90% I would guess) that you would hear the “swoosh”. Just like when you kink a garden hose. If you head nothing, that’s not sounding good. You really have to listen closely though. I would say a 1/2 a second to close it, maybe a full second.

It’s possible the circ is fighting sludge.

Did you try turning the other aquastat down to 130 yet? Making steam on a hw call isn’t good for a number of reasons

if your system is set up the way I would think it is, you’ve got two aquastats.

A- One is for your domestic hot water temperature, the temperature that comes out of your faucets. I believe you said it was set at 120 earlier.

B- The other is the aquastat keeps the boiler water from getting too hot/causing a boil. Two completely different functions. I believe you said it was set at 140 earlier.

It’s conceivable that the boiler loop (B) aquastat is not functioning properly. One hunch I have is simply turning down 140 down to 130, and see if the still boils. If it’s still boils, try turning it down another 10°. Obviously, it will take several hours for the boiler to cool down so this experiment may take a day or two depending on how much ambition you have, running up and down the stairs to your basement.

The trick is- You want the boiler water hot enough to get good heat transfer

but if it’s too hot, you start steaming, wasting fuel

The boiler's aquastat looks like it its 24 VAC wiring. There are many ways to verify the boiler's aquastat's functionality. You could generate a long DHW (Domestic Hot Water) call for heat eventually the circulator should remain running and the boiler would shut down. You could disable the power to the circulator to speed up the process, disconnect the Argo relay's terminal 4 120 VAC to the circulator. Be safe shut the power off to the boiler when making any wiring changes.

With that Argo switching relay I would suspect the system is wired like this.

The space heat thermostat goes to the Boiler's T-T terminals, which looks like it may be a Brown and a Blue wire (see below).

The "Spare XX" relay contacts of the Argo relay (two wires) with one side going through the Boiler's aquastat (in series), is also connected to the boiler's T-T wires.

So a space heat call for heat fires the boiler as long as there is a space heat call for heat making steam. This does not use the Argo relay.

When there is a DHW call for heat, the Indirect's aquastat closes which is connected to the Argo switching relay's "Thermostat" terminals TR and TW in the drawing below. This does a few things, it energizes the Argo relay, which in turn powers the circulator motor for the entire DHW call for heat, and also closes the "Spare XX" relay contacts firing the boiler. In the summer the boiler's water temperature is limited by the boiler's aquastat which is wired in series with the "Spare XX" relay contacts. So if either the "Spare XX" relay contacts open (DHW call terminated) or the boiler's aquastat contacts open (aquastat's set temp reached) the boiler's burner will shut off.

The space heat Thermostat could be wired through the 24 VAC side of the Argo relay (terminal 6, NC) to provide a DHW priority to help minimize circulator cavitation. That would let the Boiler's water cool down to the boiler's aquastat's setting during a DHW call in the winter. All depends on how savvy the person was that wired up the system.