Steam/Hot water baseboard

DRG100 · February 3

The contractor that maintains my steam boiler says I don't have a problem, I think I do. My thermostats are programmed for 58 degrees over night and 65 for the steam zone and 68 for the baseboard zone during the day (the baseboard zone is my living room, the steam zone is the rest of the house). When it's below 20 degrees both day and night in spite of the thermostat programing the steam zone is at 4 to 6 degrees above programing and the baseboard is at 68. I think that instead of relying on the aquastat to maintain the hot water for the baseboard zone they are actually firing the boiler to full steam pressure when ever the baseboard zone calls for heat.. This causes the pressuretrol to shut down the boiler periodically to keep it from becoming a dangerous situation. It sometimes takes up to 3 or 4 hours for baseboard zone to recover from the overnight temp. I believe it's also raising my my natural gas bill, which is also up, astronomically to begin with. Am I crazy or is this the way it's supposed to work? Thanks!

ethicalpaul · February 3

the steam boiler should not create steam when the hot water loop alone calls for heat.

It sounds like that might be the issue. I have seen systems that do this even in my short non-career.

Any competent hvac plumber should be able to solve this easily

Grallert · February 3

That's a huge set back. How is the water loop piped? Through the tankless coil or a separate loop using the condensate of the boiler? What's controlling the water temperature for the water loop?

pedmec · February 3

Does the baseboard heating loop relay have a aquastat installed in series with the gas valve circuit? the aquastat prevents the boiler from creating steam by controlling the temperature of the heating loop water temperature.

Big Ed_4 · February 4

Coldest day of the year … Heat loss and lack of radiation normally is the reason for the lack of heat in the past weeks …. Set backs are not helping , takes too long to bring the room back up to temperature in this freeze….

EBEBRATT-Ed · February 4

Too much set back especially when it is cold.

As far as controlling the boiler this is what you should have:

1 When the thermostat calls for heat for the HW zone the circulator starts and the boiler starts. There should be an aquastat (high limit) in the BOILER WATER to shut the boiler down if the water temp exceeds 190F as you don't want to make steam when the HW loop calls for heat.

When the steam thermostat calls for heat the HW aqustat above should be bypassed to allow steam to be made. The boiler will cycle on pressure if need be.

When both zones call at the same time you need a bypass on the HW loop (manually adjustable valves) to make sure the HW loop does not get to steam temperature

EdTheHeaterMan · February 4

If properly connected the hot water zone can never make steam. if that is happening, then you need to have the control wiring checked.

Is this a new problem or has this always been an issue?

You want to see if you have wiring like this:

Screenshot 2026-02-03 at 10.47.24 PM.png

I am not sure what steam boiler you have but the thermostat wires are all that you need to look at. in this boiler the thermostat gets connected to Y and G on the boiler wiring diagram. the thermostat for the steam heated area should be connected to Y and G as indicated in the instructions.

The thermostat for the hot water setion should be connected to something that will operate the circulator pump and have an extra set of contacts that can turn on the boiler. The important part is the Red Box. That is a water temperature control commonly called an aquastat. Set that temperature at 180° or lower and the baseboard thermostat can not make steam. The aquastat will stop the burner at 180° and will never make steam. Only the main thermostat can make steam.

EdTheHeaterMan · February 4

@DRG100 said "When it's below 20 degrees (outside) both day and night in spite of the thermostat programing the steam zone is at 4 to 6 degrees above programing and the baseboard is at 68."

This is a concern. Perhaps the aquastat is not set properly or is not connected properly. It does sound like the steam boiler is operating off of the hot water thermostat and making steam if the steam heated areas are above the thermostat set point. Check to see if you have a circulator relay and if that relay turns on the burner and if the aquastat will shut off the burner by turning the temperature down on the aquastat. Do this test with the steam thermostat turned off or all the way down to the lowest setting.

Let me know what happens.

DRG100 · February 4

I've had no end of problems with the company that installed and maintains the boiler. It takes years to get problems addressed. This the 4th. They seem too think I'm an idiot. Gotta find a new company. I'm on Long Island, NY, if someone has a recommendation let me know. This problem started when the boiler was replaced.

Boiler is Burnham Independence. There is an auto fill. Shortly after it was replaced I replaced the thermostats with WI-FI ones. The one for the hot water zone required a new wire run. The "new" addition was added in 1969 and the electrician used Romex. I replaced with thermostat wire (I was an electronic engineer for 27 years). I kept the same connections except the addition of the +24V. The thermostat connects to a terminal strip in a Taco Box. There is another pair of wires leaving the "Taco Box" going to an electrical box outside of the boiler with a transformer (+24V step down?). I do not intend to poke around in the high voltage areas!

There is no loop around the boiler. Looks like all of the hot water plumping is connected below the boiler water line. I can provide photos on request.

I always believed that the hot water thermostat should operate the circulator pump only and let the aquastat control the boiler water temp with the steam thermostat overriding when needed.

ethicalpaul · February 4

Drop any contractor that thinks you're an idiot. Honestly with your engineering background it may be less work and frustration to learn everything you need to know yourself (it sounds like you are already over 1/2 way there).

What you have is a "hot water zone attached to a steam boiler".

There is no loop around the boiler. Looks like all of the hot water plumping is connected below the boiler water line.

This is correct. Since the steam boiler is open to the atmosphere you can't pipe things the same as a hot water boiler.

Here's an article from Dan the creator of this web site that I found very helpful in making my own hot water zone off of my steam boiler:

https://heatinghelp.com/systems-help-center/how-to-run-a-hot-water-zone-off-a-steam-boiler/

Steam/Hot water baseboard

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