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Old 10 Series Honeywell to new Honeywell

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I cant seem to wrap my head around the wiring for a new Honeywell digital thermostat from an old 10 series. I have a red, white and blue wire. If I don't connect the blue I get nothing and if I do connect it to o/b it wont shut off my heat. Red connected to R and white connected to W. Using an old boiler, just radiant heat. I have tried many combinations of wiring and I cant figure it out. The relay from the boiler is R19A7K 115 volts.

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  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,634
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    Send a picture of the relay if you can.
    Was your old thermostat connected to an oil burner stack mounted control or to a switching relay? Stack controls with R, W & B can use a 2 wire thermostat connected to R & W. Not sure which relay you have.

    If the relay requires a three wire input you may have to change it or you could have a bad relay. Try this

    Disconnect the thermostat wires from the relay and use a piece of wire to jump the R & W terminals. If the relay does not work replace it.

    Post a picture of the relay so we can see what you need to replace it with.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,634
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    Looks like you need a Honeywell RA845 relay to replace what you have but post a picture.
  • HunterG08
    HunterG08 Member Posts: 2
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    here is the relay:

  • Big Ed_4
    Big Ed_4 Member Posts: 2,807
    edited November 2023
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    Use the Blue and White ... The Red powered a small heater.. ((small disks , colored for size)) ... in the old thermostat . It was an early heat anticipator or to put it in todays words ....It cycled the thermostat .....

    There was an error rendering this rich post.

    mattmia2
  • Steamhead
    Steamhead Member Posts: 16,904
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    ISTR when using a 2-wire thermostat with these Series 10 controls, you hooked it to R and B.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,634
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    And if you need to replace the relay you can use a Honeywell RA89A. The wiring on the new one is the same as what you have except it will work with a two wire thermostat
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,634
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    @Steamhead

    Pg 250 in Burkhardt's book. Had to look it up myself couldn't remember.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,124
    edited November 2023
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    I learned about the series 10 this way. W - B means Will Begin. W - R means Will Run

    In order to keep burners from short cycling the series 10 was designed with a holding circuit that was tapped into the control transformer at the mid point. This was enough power to hold a relay circuit closed but was not enough to pull the relay in. So when a call for heat was completed both the W>R and W>B contacts were open. As the room cooled the first set of contacts in the thermostat that would make were W>R. That would not pull the relay in because it's connected the lower current portion of the control transformer with the common (W) side of the control transformer. When the room temperature dropped further the second set of contacts closed W>B and the relay or other control would pull in the burner contacts. As soon as that happened the burner would fire and the heat would start to go into the ductwork or radiators. In pretty short order the W>B contact would open but the W>R contacts stayed closed and HELD the already connected relay contacts in place. After the call for heat was completed, the W>R contacts would open.

    When Honeywell introduces the Famous Honeywell Round Series 80 Thermostat with the mercury bulb on the bimetal coiled spring, they were using the weight of the mercury as a seesaw to create the differential that the series 10 created with the holding circuit

    The EASY FIX with the Series 10 to Series 80 controls is that all you needed to do is drop the B wire from the circuit and just use R and W on the old Series 10 control with the new Series 80 thermostat.

    In order to prevent overshooting, most of those thermostats were equipped with a Heat Anticipator that you would select or adjust, based on the current draw of the control you were connecting the thermostat to.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • Big Ed_4
    Big Ed_4 Member Posts: 2,807
    edited November 2023
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    This brings me back ... Thanks Guys

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