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Is there thermostat such that it turns the boiler off before the circulator?

Jersey2 Member Posts: 162
My very old boiler turns off at the same time the circulator turns off once the heat requirement is met. That wastes heat because the boiler is now very hot and that heat is not used it gradually radiates away. Is there a system that allows the circulator to run until the heat requirement is met, but the boiler is turned off 5 minutes (or some settable time before the heat requirement is met) before the circulator is turned off? Then the heat of the boiler would be used even though it is not running.
I'm not a plumber or hvac man and my thoughts in comments are purely for conversation.


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,247
    New aquastats have thermal targeting and as they learn will turn off the burner (oil) and let the residual heat finish the cycle
    Energy Kinetics leads they way with their boiler/control designs.
    rick in Alaskaszwedj
    JUGHNE Member Posts: 10,791
    A aqua stat strapped on the supply pipe and wired across the pump relay will keep the pump running after the tstat shuts the burner down, until the water cools down.
  • Gilmorrie
    Gilmorrie Member Posts: 180
    The residual heat in the boiler after the burner turns off, is not lost. First, the "lost" heat goes into the homes's inside space, even if it is via the boiler room, which eventially helps. And then, when there is the next call for heat, whatever heat is still in the boiler will be used for the next cycle.

  • Steamhead
    Steamhead Member Posts: 16,248
    Gilmorrie said:

    The residual heat in the boiler after the burner turns off, is not lost. First, the "lost" heat goes into the homes's inside space, even if it is via the boiler room, which eventially helps. And then, when there is the next call for heat, whatever heat is still in the boiler will be used for the next cycle.

    Not all of it. Some of this heat is lost up the chimney, unless there is a stack damper.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    HVACNUT Member Posts: 5,253
    Can you post some pics of the boiler and controls? Its possible the limit is set too high so the flame (gas or oil?) stays on for the duration.
    Or return temp is too low. Are you able to check supply and return temps at the boiler while the heat is running?
  • HomerJSmith
    HomerJSmith Member Posts: 2,266
    edited November 2019
    I'm cheap so I find cheap ways to do things.

    I would use a fan control with a single pole normally open relay and a thermodisc that will open at the desired temperature that you want the pump to stop moving water. the pump would be connected to the relay on the fan control and to the aquastat relay. Both connections must be on the same electrical panel buss. The thermodisc would be strapped on the outlet of the pump and connect to the transformer secondary on the fan control between the transformer and the relay.

    The way it works--the aquastat on a call for heat would turn on the pump relay energizing the pump and when the temp of the water exiting the pump reaches the close temp of the thermodisc the thermodisc points close energizing the pump, too. As long as the power from the aquastat on the boiler and the fan control are on the same side of the buss everything will be ok.

    The call for heat is satisfied, the aquastat relay opens cutting power to the pump, but the thermodisc is still closed which keeps the fan control relay supplying power to the pump. The pump continues supplying hot water until the water exiting the pump falls below the temperature that the thermodisc opens cutting power to the pump. Walla.

    Of course, you can get a Taco Switching Relay like a SR501 instead of a fan control and use the thermodisc in place of the thermostat connection on the SR501. Same buss, tho.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,247
    How is all of that easier than a strap on aquastat?
  • HomerJSmith
    HomerJSmith Member Posts: 2,266
    Ya, Steve, I can see that. How would your sequential operation work? Inquiring minds want to know.
    JUGHNE Member Posts: 10,791
    I did the strap pipe mounted pipe aquastat because this was a converted gravity system with 2 4" supply lines, cast iron boiler without vent damper, and the building was used only in the morning as an office. The intent was to milk all the heat out of the large piping and boiler because it virtually shut down until the next AM.

    The tstat would call for heat....boiler comes on via 24 vac from tstat...also energized pump relay. Aquastat is open at this time, it is wired across the NO contacts of pump relay. Tstat or boiler limit is satisfied and fire off....boiler relay off. But by now aquastat closed and continued to run pump until supply cools down as desired. One device and a couple of wires did it.
    EBEBRATT-Ed Member Posts: 13,797
    What @JUGHNE said is the best way out.

    I have done this many times.Use a strap on aqustat set so that the pump will run when the water temperature is over 130 deg (you don't want to cool the boiler below that) so you need a "reverse acting aquastat" one that closes its contacts on a temperature rise

    To much heat lost to the basement which does keep the basement warmer but some heat is lost up the stack while the boiler is sitting there hot.

    With the aquastat wired in the thermostat will start the boiler and the circulator the thermostat will stop the boiler when the stat is satisfied and the circulator will continue to run( until the boiler cools to its setpoint (130) set on the new aqustat
  • Dave H_2
    Dave H_2 Member Posts: 527
    edited November 2019
    Depending upon how your system is controlled or zoned; Zone Valves or Zone Pumps;
    You can use either the ZVC-exp or the SR-exp controller that has Post Purge Operation.
    What that means is when the last zone is satisfied, it will automatically take the Priority zone and turn it on therefore taking the extra energy in the boiler and putting it into the indirect tank to be used for Hot water in the house.

    Dave H.
    Dave H
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 6,063
    HAY... @HomerJSmith
    This is what @STEVEusaPA is talking about
    and i think it is cheeper then a switching relay or fan center and a thermo-disc because the L6006 is rated for line voltage limit and reverse operation.

    very simple to use the make on temp rise/break on temp fall contacts on the L6006C strap on Aquastat.

    Can work with any circulator relay to remove heat from large mass boiler and dump it to the radiators.

    You don't want to do this if you have a tankless coil making your hot water. of if your boiler is designed to maintain temperature for any other reason.

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    JUGHNE Member Posts: 10,791
    Is that L6006C rated for a dead short? Looks like that is what will happen. IMO
  • HomerJSmith
    HomerJSmith Member Posts: 2,266
    edited November 2019
    JUGHNE, very observant. The grounded conductor (white wire) is always connected. The switch is on the black wire. To use the Honeywell L6006C, the make on temp rise micro switch has to be connected to the motor black wire connection and to the 110V power into the aquastat black wire connection point, L1. Polarity is maintained.

    Did I mention that I was cheap? An Aquastat is 5 times more expensive than a fan control and thermodisc. Well, maybe 4 times. But, then again labor counts. But isn't the homeowner's labor free?

  • HomerJSmith
    HomerJSmith Member Posts: 2,266
    edited November 2019
    By the way a 110V 2 conductor circuit doesn't have a neutral. Only 220V single phase has a neutral. But, you do not always need a neutral wire.
    JUGHNE Member Posts: 10,791
    Just FYI, the only way you get 110/120v IS to have a neutral. White wire, (groundED BTY) and a black hot. That hot is one leg of a 220V single phase system.
    220V single phase may not need a neutral (again groundED) for operation.

    To differentiate between groundED (typically white) and groundING (green or bare)......... GroundED white does carry current as return and groundING green is non current carrying safety conductor.....carries current in the event of a fault to trip the breaker.

    That is the way it has been since before I was licensed in 1969.
    But the next code cycle is changing the terminology, the white and green function will not change, just the wording?????
  • HomerJSmith
    HomerJSmith Member Posts: 2,266
    edited November 2019
    I have dig out my NEC book. The NEC refers to a single phase 110V white wire as a grounded conductor. One of the questions on a licensing exam is "What is the difference between a grounded conductor and a grounding conductor?"

    A neutral wire on a 220V sys. is two 110V legs 180 deg out of phase. When the current on one leg is the same as the other leg, no current flows thru the grounded conductor, therefore it is called a neutral white wire. That was my understanding. My codes are older. It's hard for me to believe that the NEC would switch on calling the white wire on 110V circuits to a colloquial term when neutral is specific to 220V circuits.