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Burner Control Problem while converting to a Digital Thermostat

I have an oil furnace with a Honeywell R8184G4009 burner control and conventional T87 "Round" heating/cooling thermostat. Recently changed out the stat with a digital smart stat RTH9580WF, which like many newer stats requires a connection to the common or neutral on the 24V transformer. Original wiring did not have a "spare", and the red and white from the burner control runs back to the stat and connects to Rh and W respectively, and the blue wire from the 24V transformer power to Rc on the stat. Y and G were both connected to the stat as per color code. Modifications to the wiring included intercepting the white at the furnace from the burner control and connecting to 24V transformer common, which essentially ties one side of the burner control T circuit to C and also allows the stat wire W to carry C to the new stat (connected to C), while Blue (carries 24V power) was connected to R on the new stat. Furthermore wire R was tied to W on the stat to carry heat call to the burner control, and the Y and G wires correspondingly to Y and G on the stat.

Unfortunately, upon calling for heat it did not take long before the burner control failed. I suspect the current to the control is too high, but no compensation or adjustment is available on the stat, nor have I found anything online that addresses this issue. The old stat does have an anticipator on heat, the cool side has a 4700 ohm resistor, and as many may know, the heat side is adjustable. These both add resistance to each of the circuits. I believe the solution to make the new stat functional is to place resistance into the heat control circuit; probably on the white wire running to the burner control. Also, it seems a resistor may be needed on the cooling circuit to equal the old stat characteristics, but this is a question for the experts as well. Noteworthy, all control circuits (W, Y and G) terminate at 24V common after passing through their respective relays. Cooling and fan work fine based on limited testing.

Thanks in advance for any suggestions to remedy this condition. I imagine others may also benefit, as technology is being introduced to older systems.

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 17,736
    edited October 2020
    T-T on the burner control is looking only to have a closed or open circuit at the other end. C needs to be a common return -- that is, connected to ground.

    The old reliable T87 did have an anticipator for both heating and cooling -- but basically it was a switch, either open or closed (the heating/cooling variety was SPDT -- single pole, double throw. R is the common, and W and Y are the two throws). On the heating side, when the switch was closed it allowed current to pass through the heating (adjustable) anticipator, heating it. The cooling anticipator (that 4700 ohm resistor)(not adjustable), on the other hand, allowed a small current to flow (from R to Y) when the thermostat was NOT calling for cooling, and was cut out of the circuit when the thermostat was calling for cooling.

    Your nice new thermostat needs an independent common -- C -- from the 24 VAC transformer, although some of them can be made to work -- after a fashion -- using a resistor to allow current to flow to the thermostat when it's not calling for either heat or cooling. Adding a resistor in series on either side isn't going to do it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,444
    edited October 2020
    You’re wiring it wrong. Don’t you have a fan center as one of your controls, if you have a furnace and an ancient Honeywell 8184G?
    If you smoked the primary control you can have your service tech switch out your control to something modern that has what you need and simplify your wiring.
    steve
    HVACNUT
  • Steamhead
    Steamhead Member Posts: 15,025

    You’re wiring it wrong. Don’t you have a fan center as one of your controls, if you have a furnace and an ancient Honeywell 8184G?
    If you smoked the primary control you can have your service tech switch out your control to something modern that has what you need and simplify your wiring.

    Agreed. That R8184G needed to be replaced anyway- its trial for ignition is probably 45 seconds, whereas current standards call for 15 seconds.

    The "fan center" is probably a 4-inch-square unit with a transformer and a relay on it. Does your thermostat cable connect to such a unit?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • Big Ed_4
    Big Ed_4 Member Posts: 1,827
    I would , , run a new 18/7 wire (always run a spare ) . or Take.... lets say the G fan and use it for a common and jump the Y wire which powers the condenser to power the fan relay too ... But you will loose the control at the thermostat to switch fan to manual on ..
    I have enough experience to know , that I dont know it all
  • refiner49er
    refiner49er Member Posts: 4
    Thanks for the comments. Running a new wire would be challenging without surgical techniques, lol. Also, the new stats have air circulation features which I would like to advantage at times. However, I wonder if the heat call from the new thermostat (24V) could operate a compatible SPST normally off relay, which in turn can provide the burner TT circuit with the desired open/closed signal?
  • Big Ed_4
    Big Ed_4 Member Posts: 1,827
    edited October 2020
    You can add a relay to close TT on the primary relay ... I would use a RIB relay

    I have enough experience to know , that I dont know it all
  • refiner49er
    refiner49er Member Posts: 4
    Thanks Ed, I also see a more modern burner control, Honeywell R7284B1024 and it is actually less expensive than the 8184. Looks like this would be the upgrade to it's predecessor. The question in this case is whether this control is similar regards to the TT circuit, or could accommodate a 24V heat signal? I certainly won't make any assumptions from this point forward... ; )

    The frustration that led me to post is there is no guidance or specs pursuant to NOT using 24V to actuate a burner control, nor could I find information online that discussed changing over to a digital stat. In any event, thanks again for all your input!
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,444

    Thanks Ed, I also see a more modern burner control, Honeywell R7284B1024 and it is actually less expensive than the 8184. Looks like this would be the upgrade to it's predecessor. The question in this case is whether this control is similar regards to the TT circuit, or could accommodate a 24V heat signal? I certainly won't make any assumptions from this point forward... ; )

    The frustration that led me to post is there is no guidance or specs pursuant to NOT using 24V to actuate a burner control, nor could I find information online that discussed changing over to a digital stat. In any event, thanks again for all your input!

    Which is why people call on a professional when they have an issue.
    steve
  • Steamhead
    Steamhead Member Posts: 15,025

    Which is why people call on a professional when they have an issue.

    THIS!

    @refiner49er , where are you located?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • refiner49er
    refiner49er Member Posts: 4
    All over the place actually, between SE of Cleveland and Vancouver Washington. Also working on a interesting new project which will be deployed in East Africa next year, dehydration of fruits and vegetables using heat pumps, coupled to a hydronic circuit with CHP and solar. Will be a totally energy independent, aside from a small diesel generator for primary power. May add biomass or biogas as a future upgrade, however we are starting "simple" with the first pilot plant.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 11,095
    I agree with @Big Ed_4 about using a relay. Different transformers can play nice together if wired correctly (the Taco 3 wire zone valve come to mind) But I don't like mixing transformer power from two transformers. It makes it more difficult to troubleshoot and I usually avoid that