Hot water zone off steam boiler

safir1979 · April 9

Need some help i have a hot water basement zone off steam boiler for some reason its producing steam to the upper floor when its calling for heat I have a aquastat installed set at 180 but that does not help

Jamie Hall · April 9

Wiring problem or problem with aquastat. Can you diagram the wiring for us? What connects to what?

safir1979 · April 9

yes when I get home thanks

EdTheHeaterMan · April 10

On a call for heat from the water baseboard zone there should be a control that stops the burner when the water temperature reaches 160° or 180°. That way the burner can not operate at a high enough temperature to make steam.

A detailed wiring diagram can be provided for this logic once I know what boiler and burner system you have. Also what thermostat operates the baseboard water loop? Picture of the boiler from far enpugh back to see the piping and the controls from 2 or 3 different angles will help

safir1979 · April 10

thankyou will do soon it’s a crown Bermuda steam boiler

Grallert · April 10

To be clear. You have a steam boiler and have run a water zone off of that boiler? That water loop is getting steam and is loikely banging I would guess. Could be a mixing issue. That water loop should have a bypass so as to prevent boiling water from entering the zone and potentially flashing to steam.

Are my assumptions correct ?

EdTheHeaterMan · April 10

I'm not sure if this is your exact wiring diagram from Crown Boiler by Velocity Boiler Works, but if it is, I have added the controls needed to operate the circulator pump and the burner so your thermostat from the water zone will not make steam.

The yellow highlight is not part of the factory diagram. It has the three controls needed to operate the circulator pump. A thermostat for the water zone. a circulator relay and a Aquastat like the L6006C to stop the burner before it gets hot enough to make steam.

You will also want to read up on how to do this because the circulator location as close to the floor as possible is important so there is less chance of cavitation when the steam thermostat makes the water heat to 215°F and the water zone is operating at the same time.

Is this something you just added or has this been here for some time and the problem just started to happen recently?

Hope this helps.

STEAM DOCTOR · April 10

Has it always been making unwanted steam? Is this a new problem or an old problem? Is the basement zone working properly? Where is the aquastat located, in the boiler block itself or in the loop piping?

safir1979 · April 11

Hi, I will update today with pictures and wiring diagram exactly the way it is thanks all for helping

safir1979 · April 13

safir1979 · April 13

Hi, all I am attaching pictures thanks

tcassano87 · April 14

is this a new issue?
You’re 100% certain the upstairs thermostat isn’t calling?
Do you know how old your aquastat is? Can be be off to a certain degree and if it’s malfunctioning or giving incorrect readings the temps could be getting to high, could also be completely broken.
Nipple Could also be clogged and not allowing the water to get to the probe so it’s not sensing the temperature correctly
Turn the heat on and turn the dial back and forth to see if it turns the boiler off like it should. Can try to put some heat conductive compound on the probe but it’s very possible you need a new aquastat

safir1979 · April 14

I installed the system about two years ago honestly and it was not cutting off at 180 degrees so I did replace the Aquastat about a year ago thought that was the prob but it’s not and yes I turn down upstairs thermostat to test

EdTheHeaterMan · April 14

I'm not sure that the aquastat location is the best choice. the boiler temperature and the temperature where the temperature is being sensed can be over 30° different which will make steam and the aquastat is still allowing the burner to operate. That will depend on the distance from the boiler and if the pump is operating and how fast the heat will transfer up the Tee fitting until it reaches the actual temperature probe.

Screenshot 2026-04-14 at 11.23.29 AM.png

Please take a close look at the position of the temperature probe that I have superimposed inside the pipe. The water temperature you are measuring is from the bottom of the boiler, flowing past the tee fitting and then to the circulator pump. You are not measuring the water temperature in the boiler near the surface of the water, where the steam is generated.

~~What model number is your boiler.~~ There is a better place to install that aquastat.

never mind, I found it above.

EdTheHeaterMan · April 14

wiring diagram update to your diagram posted:

I believe your system wiring is correct. The problem is in the aquastat location.

This diagram in the manual shows that the Aqustat location for a hydronic loop (the indirect in this case) is located in the boiler, not on a tee outside of the boiler.

It is above the larger return tapping, but below the water line. Also there are specific tappings on the boiler for taking a hydronic loop off of the boiler. see Figure 3-3 tapping P is for the control. Tapping M and N are where your circulator and retur pipes should be located.

Since you did not use the proper tappings, but the system is heating the baseboard loop, I would not stress over that piping. I would just try to remove the 3/4" plug from tapping P and install your aquastat there.

Hot water zone off steam boiler

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