water level after heating cycle

Shouldn't. The usual observation is that during steaming the water level will be lower than it was — perhaps a fair amount lower — but then recover more or less rapidly afterward. If there are long or partly clogged wet returns, it can take a surprisingly long time.

Now. If the water level comes back eventually to higher than it started… if there is an automatic feeder, it may have gotten triggered.

Not exactly sure what you are asking but I will give this a go.

cold boiler, radiators fill with air, water is at the proper water line. Am I right so far?

burner turns on and makes the water turn into steam. the water that turns into steam leaves the boiler and goes to the radiators. The radiators get hot and the steam gets cooler and turns back into water (called condensate). The water line in the boiler drops a few inches as a result of the leaving steam.

The condensate in the radiators makes it way back to the boiler and the water line goes back up some.

The burner stops and all the condensate returns to the boiler and the water line gets back to the original level. no higher and no lower.

That is the perfect way to run the boiler. SO… The water line does NOT go higher

What if?

cold boiler, radiators fill with air, water is at the proper water line.

Burner turns on and makes the water turn into steam. The water that turns into steam leaves the boiler and goes to the radiators. The radiators get hot and the steam gets cooler and turns back into water (called condensate). The water line in the boiler drops a few inches as a result of the leaving steam.

The condensate in the radiators takes too long to make its way back to the boiler and the water line goes down more and the water feed valve adds water. the burner continues to make steam.

The burner stops and the all condensate returns to the boiler and the water line gets back to boiler with all the extra water added during the heating cycle from the auto water feed

Now the boiler is cold and the water line is a few inches higher as a result of the added water.

Does this sound like your problem?

I would suspect the return line could be partially plugged. Do you have any 'wet Returns"? That would be return lines below the boiler water line or perhaps under the basement floor?

If the water line is rising, you may not have a leak. You likely have a clogged wet return. A lot of gunk and mud can build up in under-floor wet return piping.

If you have someone clean those pipes so the condensate can return to the boiler more quickly, you may then discover a leak. The debris that was removed may have been plugging holes in the under-floor return pipe.

Get the pipes cleared out, but be prepared to pay for new wet return piping. Copper pipe can be used for wet returns as long as all of it is below the boiler’s water line.

That small drop is normal. That is because the water is changing into steam and going the the radiators.

If the burner stops because the water level drops, then the water level goes back up because automatic feed valve adds water, then you will get higher water level after everything cools down.

Does the water level stay at the higher level for a long time if the burner is off?

Does the water level go down when the burner is off for a long time?

These answers will determine if you have a leak under the floor.

I'm still confused, @ups3341 , but what I think I'm reading is that the water level does drop when the burner is off for a long time.

The only way that can happen is that you are losing water somewhere. Now it may not be a big leak — a surprising amount of water can escape from valve stem packings and even vents when the boiler is running. But.. there may be a real leak somewhere, too. If you or your water feeder needs to add mor than a gallon of water per week, then it's time to start looking.

So with these answers I am getting a better picture (idea in my mind's eye) of what might be happening.

To be clear:

1. Boiler runs and heats building properly
2. Boiler stops and cools down after building heat is satisfied.
3. Wait some time and water lever is higher (because the condensation from radiators takes some time to return to boiler)
4. Water in boiler is higher after short wait time
5. Water level drops after long wait time .

This is what I understand from your answers so far. Please make corrections if I am wrong

Does the water level stay at the higher level for a long time if the burner is off?

No.

Does the water level go down when the burner is off for a long time? Yes.

A lot of times the burner is off the water at the red line

You indicate this :

The boiler should not refill water any time in the week.

Is this a question? The answer depends on your boiler system. If there is an automatic water feed valve, it can have water added anytime that water feeder gets a signal that the water is too low.

And to help with possible language issues, the "Wet Return" is all the return pipe that is below the water line, as in the diagram above. The name of that pipe is the "Wet Return". It's called "wet" because it's always got water in it.

no, there’s no problem with Ed’s post but the original poster earlier seemed to confuse Wet Return with a return that is wet

Ed is right. But assume all is built correct, or is not compromised in any way, the system has three states of operation. All on, all off and in between. Off and steady on could show a stabilized level but be different. But there is a time lag between startup steady, to shut down cold. In between is always changing. Given all of this the question asks, what is normal for this? Here is where the most important diagnostic tool is needed that is almost never done. A complete operation report recording all those little details. With this, we can compare new installed to what we see currently. But this will never be done except maybe by Government and a lab. We'd be lucky to even get a combustion test. But its not just design, there are changes in combustion rate and design that can affect steam dynamics. Is it a rolling boil, or a simmer? Does it cool fast or slow? Just changing any component like a boiler, burner or even a few radiators can make a change. Some tweaking is always needed in a new install. So who will set the settings, size the devices, this all will matter. It is why diagnosticians will always be in demand. If we really want to know and spend the coin to find out. But my experience is hearing, "Its working don't touch it!" And then the boiler room door closes and everything changes again.

It was Ed, and thanks for noticing.