Isolation relay for the oil furnace

[@alanshamoun5577]

Thank you so much! 4 years old and still relevant and helpful. I couldn't figure this out by looking at diagrams, and could not find any helpful photos. This video tutorial was great.

[@67NewEngland]

You should put the words "C wire" in title. You'd get a million views. Tons of people asking/looking for solution to t-stats needing a Common wire.

[@JSunSea]

Thank you for helping me install my Ecobee3 lite thermostat. Your tutorial was extremely helpful and gave me the confidence I needed to complete my installation with your KZbin presence. My old 1928 gas burning boiler never felt newer!😁

[@grayfurnaceman]

Glad it helped. GFM

[@josequintero7971]

Omg thank you very much! I had a idea of how to wire it but this just confirmed it! Like the other comment said, a lot of people need this information.

[@joetamzarian1817]

Just hooked up my new smart thermostat to my old oil furnace and this worked like a charm! Thanks

[@grayfurnaceman]

Glad I could help. GFM

[@jeffreynewton9157]

Great video. I have the exact set up on my furnace. Now I know what an Isolation relay is and does. Thanks.

[@Batti2323]

This is just what I needed! I think a schematic might be helpful, but I can get it from here. Thanks for all you do! You have saved me some real money.

[@grayfurnaceman]

Welcome GFM

[@ianagar805]

Best HVAC education videos out here! Videos help so much!

[@EddieLeverich]

You did a very good job explaining this!!

[@grayfurnaceman]

Sometimes I don't know if I am getting across or not. Thanks. GFM

[@dieselhater]

Use those alot when replacing a 8184M control with the large transformer. When we install a newer furnace with a regular control alot of times there is only four wires at the thermostat. So we need the relay to isolate the oil burner control from the AC relay.

Most all older furnaces need to be isolated from the new programmable thermostats.. In my home I have two furnaces where one powers the touch screen thermostat and the other must be isolated from it with relays that initiate the call for heat and the manual operation of the blower fan from the thermostat to circulate air when desired.. The problem I ran into was that the signals to my relays were 24vac and very low in amperage.. This low power was not enough to keep my isolation relays activated so they would chatter like crazy so I had to add a 1/2 wave rectifier and a capacitor to turn the weak AC into DC at about 12v which solved the problem since an AC relay coil does work with DC.. You can use a diode and capacitor or you can use a voltage rectifying transistor.. Another option if you don't already have the relay is to buy a solid state relay which requires less current to switch..

[@twitter.comfixwifi992]

Thanks for the advice, and it works great. A extra isolation relay could be used for another smart thermostat if it's wired in series. Honeywell had a outage for several hours recently, couldn't control the primary thermostat that operates the auxiliary heat oil furnace when it's below below 34 degrees, and the heat pump when it's above 34 degrees. The extra isolation relay would allow me to use a Sensi smart thermostat in series after the (Honeywell isolation relay) so there would be a option to lower the temperature below the Honeywell thermostat. W 2 connected to a outdoor thermostat routes the the 2nd stage heat signal to the heat pump but if the temperature drops below 34 degrees the heat signal is diverted to the isolation relay so it operates the oil furnace. The American Standard 4TWB3060B1000CA seems to operate on the W 1 wire without the W 2 wire but makes me wonder if it's a 2 stage heat pump?

[@raymondbailey7045]

Great video. Lots of help, keep up the good work.

[@pleappleappleap]

Hi! I installed a smart thermostat on my oil burning forced-air furnace. I got it working, but I wasn't able to figure out how to connect the thermostat into the Honeywell Fan/Limit switch. So right now, the thermostat can call for heat, but can't control the fan. Any advice?

[@perucabana]

how is for utica gas boiler with 2 wires it will be the same?

[@dritanshabani6396]

Great video you always have great and very informative videos

[@grayfurnaceman]

Thanks for the support. GFM

[@JF0913]

Thanks for sharing your knowledge

[@christopherbagge1137]

This is a great video. I recently purchased the ecobee smart si, to connect to my old new york boiler. I new I needed a third (common) wire, so I purchased the Taco SR502-4. I rewired the two circulator pumps to the Taco and initially connected my old Honeywell mercury thermostats; one for each zone, to the Taco. This worked well. Once I received the Ecobee I simply connected three wires from the Taco to the thermostat and it did not work. I needed an isolation relay to act as the switch. I used the setup you describe here. My question is, since I have the 24V terminal on the Taco could I have used that in place of the 24V transformer?

[@grayfurnaceman]

Christopher Bagge I would leave it at that. Sometimes the transformers in the controllers are not big enough for that. GFM

[@bruceleblanc8813]

Hello Could you use a fan control center such as the White Rodgers 90-130 with this set up? Thank you and great vids Bruce

[@franciscocastellanos9157]

I have found a couple of oil furnaces using a fan center control with built in relay and transformer. The primary burner ignition control terminals (TT) are connected to the W from thermostat and to the R in the transformer joined together with R from thermostat. These two furnaces have been working for years just I knew the need to use an isolation relay to prevent signaling the primary control with 24V. I could prove 24v coming to the control. This threw me out. Any suggestions ? Almost forgot to mention the C wire is not in use on the thermostat, runs with batteries. Love your tutorials videos

[@grayfurnaceman]

If by chance, the transformers were wired in sequence, the cad cell relay transformer may survive, but that would be unusual. Usually, the smaller transformer fails. GFM

[@twitter.comfixwifi992]

Thanks important information. Was wondering if I could wire up the relay, so the thermostat would make the oil furnace become the back up heat? Also what kind of relay is that?

[@grayfurnaceman]

You can. Just wire it to 2d stage on the thermostat. GFM

[@darylbroughton8761]

Could you help me I have a ADC T3000 thermostat all electric home. But I can't find an hvac to install. But it does look simple

[@MikeDellOvo]

Thank you for helpful info. My oil furnace has the TT primary control but also has a control box with c y g r mounted in the furnace with nothing hooked up to it. Would I be able to avoid purchasing a relay and transformer by just using the c and the r terminals to power the smart thermostat and then Rh and W to the TT terminals. I did test between c and r in the furnace control box and there is 24 volts there. Any help is greatly appreciated.

[@grayfurnaceman]

You can use that for a power source for the thermostat, but you will still need an isolation relay for the TT terminals. GFM

[@stevew9585]

Looking for advice. Hello, I have a Williams Oil-O-Matic Fuel Oil Furnace that I am guessing is from 1960 something. It has a Stack Relay and a Fan Limit control. I added a 2 ton Heat Pump and am uncertain about how to energize the fan for cooling or heat pump heating? I have a single speed blower that provides about 800 cfm. I understand I can install a relay between the thermostat's call for heating and the stack relay to isolate the fuel oil heating cycle from other functions. I also understand I could use a fan center which has it's own relay. The fan center N.O. and N.C terminals usually get connected to different speeds of a motor, one speed for heating and another for cooling. But I have one speed so I'm confused on how to energize the fan without over lapping the controls. Plus I have a heat pump so its one speed for three purposes.

[@grayfurnaceman]

Wire your fan center relay NO contacts in parallel with the heat operated fan switch. The thermostat should energize the fan relay thru the G terminal. GFM

[@darylbroughton8761]

My Adc t 3000 themostat reads system protect on the hear mode and the unit shuts off for 5 minutes. I have ordered a isolation relay to correct the issue. But I don't know how to install it correctly. So my unit want cut off and go in protective mode.

[@dlinberg7561]

Can you explain how I could possibly connect the issolation relay to the back up heat on my Honeywell TH8320R1003? There's a white wire connected to the back up heat terminal but I'm wondering if it's even being used. There's 12 wires ran to furnace and one set of 4 wires not stripped and not used.

[@grayfurnaceman]

Probably too complicated for a comment. But I will say the white at the outdoor unit is usually used for backup heat. It could be commented to the w2 terminal of the thermostat. GFM

[@R34l1ty4U]

I am not an electrician.... But can you explain why you need a relay plus the transformer???. I tought you could use a new 24v transformer output and connect it to Rc and C.... Then your T-T cables to Rh and W1. What am I missing?

[@JohnHolmes69]

I got it working without the relay... I am using a Google Nest. Hopefully, I will not experience any issues.

[@carolbroverman6453]

@@JohnHolmes69 Hi Can you explain how you did this without the relay? I have a very old gas boiler with just 2 wires for the thermostat. Which Google Nest thermostat do you have? The 2020 or the E or third generation?

[@JohnHolmes69]

@@carolbroverman6453 Carol, because I did not have a C wire, Google sent me a dongle that I could connect that somehow draws power from the device and allows communication as well so it works with just two wires.. This furnace is at my cottage but I found a video that talks a little about it. In the video, you may be able to see how this dongle is wired. In the video, i am asking about also allowing fan to function independently. Currently, the fan is only controlled by furnance, so I can not control fan myself (force fan on to circulate air when furnace isn't firing). Off video, we jumped two terminals and fan turned on, that is why I am asking about adding the third wire. Hope this video helps. If not, I can try and take better photos next time I am up at the cottage kzbin.info/www/bejne/jJ6ah6VojM-qmZo

[@michaelcharles4033]

Great tutorial GFM, all,I need now is to purchased the relay, so,I can get my econee3 connected to my Burnham steam boiler, btw do I need a separate Transformer or I can use the one supplied with the boiler?

[@grayfurnaceman]

You can use a White Rodgers 90-370. The one on the boiler will work if it has 40 va capacity. Its marked on the transformer. GFM

[@uncleandy9927]

I don't really see how you wired the transformer? where did the power source for the transformer come from? thanks

[@RobHVAC]

Great video and tip.

[@grayfurnaceman]

Thanks GFM

[@joshl3456]

Hey I have a similar situation I have a heating only system within ecobee thermostat which is similar to The Nest in your video but I have a relay for single-pole double throw and I was wondering if you can help me wiring it

[@riveraalvin]

great video, how do you wire it if you have 2 zones?

[@grayfurnaceman]

I think you would need 2 separate relays wired in parallel. GFM

[@josephborbone4480]

Hi Gary. Great video. This will help me signficantly. One question: you say the relay so a SPST, but when I look up that number is says it is a SPNO. What do you recommend ? Thanks.

[@grayfurnaceman]

It is both. It is single pole single throw but it is also normally open.

[@ToddFun]

what is the power supply that is in the primary control that you speak of. Batteries? What happen to the 2 big fat yellow wires connected to the Honeywell primary control and what was there purpose before your modifications.

[@grayfurnaceman]

The primary control (cad cell relay) shown has connections to the 120 volt underneath. The control has a small 24 volt transformer inside that supplies power to operate the control and send power to the thermostat. The 2 yellow wires are to the cad cell (light sensitive), that "sees" the flame to prove the flame has been established. Hope this helps. GFM

[@ToddFun]

grayfurnaceman Yup, that helps. Thanks.

[@Legalmachinist]

Thanks, this was exactly what I needed! Where would you suggest is the best place to tap the 120V supply so that it remains within the emergency furnace shutdown circuit?

[@grayfurnaceman]

If there is a 4x4 box where the power comes in to the furnace, mount it there and hook it to the black and white wires. Hope this helps. GFM

[@Legalmachinist]

Indeed, mounted transfer on cover plate on main power junction with small evilbay sourced relay next to it. The real challenge was pulling a new line to replace the two wire line but is in and the new Zwave thermostat is working on my oil/hot air furnace. Thanks!

[@grayfurnaceman]

Legalmachinist Glad it works. GFM

[@JohnBachand]

Thanks, I have steam heat with a domestic hot water coil on separate stat. Would like a smart wifi thermostat upstairs, I have at least five wires to thermostat now, only using two. Do they make a transformer/ relay pack as a one piece unit? Also, the domestic hot water stat wires are under the same two screws as the heating thermostat wires. is there any complication there?

[@grayfurnaceman]

This video explains the fan center, which has both the relay and the transformer. kzbin.info/www/bejne/bYmpo4itbN2EkLc No complication that I can see. GFM

[@michaelwright6742]

Great video. I followed this process and worked great for powering my wifi thermostat. However ever since, my fan runs all the time, 24/7. I've double checked the wiring. Any ideas?

[@grayfurnaceman]

All I can tell you is you have mixed up some wires. GFM

[@michaelwright6742]

@@grayfurnaceman Thanks, I'll check it out more.

[@GamerDjsquared69]

Great video! i have the same burner but i have a HoneyWell L7224U aquastat which the thermostat connects to that with T T terminals. I bought a 24vac transformer and looking to see how i would wire this up and would i need the relay?

[@grayfurnaceman]

You will definitely need the isolation relay. Wire it up the way the video says. GFM

[@GamerDjsquared69]

so am i eliminating the wires from the aquastat and just using the wires off the cad cell? I am just trying to clarify what i am doing. And the isolation relay i am slowly figuring out.

[@GamerDjsquared69]

And on my primary control the T T wires are jumped to each other

[@grayfurnaceman]

I think you are in over your head here. GFM

[@GamerDjsquared69]

So i am not in over my head, it was very simple. Hard wired the transformer and sent the 2 wires from that up to thermostat, and added 1 to the C wire and the other to the RH. And works perfect..

[@xJamesxKingx]

I was told i need an isolation relay bc my nest thermostat keeps losing power and not communicating to the analog oil burner. I was under the impression I judt needed the relay and not a transformer. Thoughts?

[@grayfurnaceman]

If you are trying to connect the Nest to a 2 terminal Cad cell relay, you will need the transformer. Generally, It is best to use a fan center that contains a transformer and relay. GFM

[@xJamesxKingx]

@@grayfurnaceman I'm looking at replays that say they contain a transformer. Is that accurate?

[@grayfurnaceman]

@@xJamesxKingx All cad cell relays have a transformer inside. However, if the control has just 2 terminals marked T & T, the transformer is too small to operate anything but itself. GFM

[@ramiaburoomi9513]

Gd day, I followed ur instruction on how to add a common wire. I bought the relay, connected the wires as specified. My new wifi Honeywell lit up, boiler fired up when i turned the thermostat on heat, but my three zones are not opening up. They stay closed, then boiler shuts off without circulating the heat into the house. How do i go about wiring the zones to the switching relay or what can i do to have my system up and running. thank you in advance

[@grayfurnaceman]

+Rami Aburoomi If you can send me a wiring diagram of the system I may be able to help. GFM

[@ramiaburoomi9513]

+grayfurnaceman Gd morning.. can i have an e-mail address so i can send u the diagram i drew up Thank you

[@grayfurnaceman]

+Rami Aburoomi Send to [e-mail] GFM

[@ramiaburoomi9513]

+grayfurnaceman Gd day, i sent u the diagram explaining how i connected the wires by email

[@whitegtp100]

What did you connect the transformer too? You didn’t show that

[@grayfurnaceman]

This is an add on part to isolate the thermostat from the control wiring. The R and C of the transformer is the power source. GFM

[@jvrandomvideos32]

what terminals ( + & - ) can i use on the Honeywell L8124A aquastat to power up the (Additional Transformer) ?

[@grayfurnaceman]

You can use L1 and L2 for 120 volts to power a transformer. GFM

[@jvrandomvideos32]

@@grayfurnaceman Thanks for getting back to me ! Many Thanks!

[@LubaLuba1]

I think I have a bad relay because my furnace not turning on and I can hear a low humming when I manually turn entire furnace power off and a dull click from this relay can I buy one from depot or lowes

[@grayfurnaceman]

I have seen them there. Take a pic of yours with the part # and you should be able to match it. GFM

[@TepaleJeff]

Stupid question… where do I connect the 120 part of the transformer

[@grayfurnaceman]

It goes to the incoming 120 volt power located in the junction box of the furnace. GFM

[@TepaleJeff]

⁠​⁠@@grayfurnacemanjunction box where the primary control would be or can I wire it to the switch ? Or it doesn’t matter? Thank you

[@goalie2998]

if i have a cad cell relay being controlled with old 2 wire thermostat. i plan to add a cooling coil into the existing duct work. i ran 5 conductor t stat cable to new t stat. i neex to isolate the existing cad cell relay with a relay. and add a second 24 volt transformer. to power t stat, and condensor coil. so far does this seem almost correct?

[@grayfurnaceman]

Yes. GFM

[@goalie2998]

+grayfurnaceman thanks for the help gfm! one more question the ezisting furnace is forced hkt air only. they have a transformer with all the terminations on it. including 3 violets that control the fan motor relay. however the installer bypassed the transformer and relay. my guess is they powered the fan from the load side of the cad cell relay. is that common practice? im an electrician so the furnace controls are not my specialty, however it makes sense with a little guidance.... lastly the condensor contactor. that is strictly triggered via the t stat? so i can splice the yellow t stat wire with the red going outside . and land the white on the common of my transformer.... thanks again for the help.

[@goalie2998]

+goalie2998 2 violets*

[@grayfurnaceman]

You cannot power the fan relay with the cad cell relay. It is too small. The fan was probably powered by the heat operated fan switch. You are correct about the wiring to the condenser contator. Good luck. GFM

[@goalie2998]

+grayfurnaceman thanks for your help! lots of great info.

[@plasenciaw]

do you have a wiring diagram for adding a C wire?

[@grayfurnaceman7640]

I do not. It is pretty simple. Find the common (C) on the air handler, then run a wire from that common to the common of the thermostat. GFM

[@kents4199]

Can't quite make out the model number of the White Rodgers relay. Is it 90-290Q?

[@grayfurnaceman]

Right now I can't remember. Any 24 volt coil relay will do. GFM

[@MikeLikesBeer1]

How can you tell if the problem is the relay instead of a motor or the transformer? My motor spins fine and the reset button has not been tripped. Feels like it should be a relay? What do you think?

[@grayfurnaceman]

+Mike LikesBeer If power is to the motor, the motor has either failed or the manual reset is open. No power to the motor, possible cad cell relay failure. GFM

[@MikeLikesBeer1]

grayfurnaceman I pulled the cad relay and checked the main power under the relay. there aint no power that registered on my multimeter. There is power to the system. This is the first time I have tried to run it this year. I have no idea what could be wrong with it. I checked the fuse and its good. I checked the transformer and it seems good on the multimeter 24v and checked the fan limit switch and there is power running to it. but there is no power to the fan and burner? What would cause that?

[@MikeLikesBeer1]

grayfurnaceman There is power to the fan limit switch but I dont know how to tell if that is preventing power to the motor or not?? Its an older hallmark unit and the fan limit switch is two piece. It don't look like the ones on the internet that are a one piece dial type. Mine are two strips. The only thing I have not done yet is pull the cover to the main switch where the fuse is and see where the power stops??

[@MikeLikesBeer1]

grayfurnaceman cad cell relay/primary control. I hope I got that right.

[@grayfurnaceman]

+Mike LikesBeer If power is available to the control, and with a call for heat, no power out the control has failed. GFM

[@tdavidock]

Thanks- great video. Question. In doing this on 3 zone system, I plan to tap the power from the wall mounted zone transformer. Would I still need to use the relay with the zone transformer?

[@grayfurnaceman]

What are you using the isolation relay for? GFM

[@tdavidock]

Sorry- wasn't clear. I want to install an ecobee thermostat. I need a common wire, but with my boiler's TT setup and no C, I was looking for a place to tap into for power. There is a separate zone valve transformer that I was planning to use for my C. I just want sure if I would also need to install an isolation relay since it's controlling the zone valve. I have 3 wires in the wall for this setup.

[@grayfurnaceman]

I would install the isolation relay. Using the wall mounted transformer should work ok. GFM

[@AJ-we9kd]

Hi gfm, Can I use a 24V SPDT NO/NC Relay and not use the normally open? I can always spring for the SPST for $3 more.

[@grayfurnaceman]

Of course. An unused contact never fails. GFM

[@TheGeorgeBandMusic]

hwhite, lol, i wonder if you say cool hwhip

[@fuzzyvision1219]

Hhhhwight