Oil boiler with line voltage convert to 24v

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Old 11-16-19, 04:54 AM
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Oil boiler with line voltage convert to 24v

Looking for advice on replacing my line voltage thermostat with a 24v thermostat. I've included photos of the boiler and thermostat in this Google photos link: https://photos.app.goo.gl/jGKxz83HAk9TbuCP9

I traced the wires coming in to the boiler back to a junction box by my stairs. There's a line leading back to the panel, one leading up to an emergency shut-off, and one leading to the thermostat.

Thanks for any help.

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Last edited by PJmax; 11-16-19 at 03:03 PM. Reason: imported one pic from link
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Old 11-16-19, 06:36 AM
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It’s a bit hard to tell what that control is, you could replace that existing Stat with a new line voltage one , it may be easier. https://www.homedepot.com/p/Cadet-Si...H401/202563495
 

Last edited by PJmax; 11-16-19 at 03:07 PM.
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Old 11-16-19, 07:43 AM
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I thought about just replacing it with a line voltage thermostat, but I really want the functionality of a programmable (preferably WiFi capable) thermostat. Haven't been able to find any line voltage models.
 
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Old 11-16-19, 03:06 PM
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Here's the problem.

You need three wires to operate a wifi stat. You only have two. In the picture I put an arrow pointing to the 24v thermostat connection. You could remove that jumper and connect a standard thermostat to that point. You could actually locate your heavy 120v current stat wires and move them to the 24v point but you are still missing a third wire for a C connection.

You could use a separate 24v transformer to operate a wifi stat but you still need at least three wires.
 
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Old 11-16-19, 04:15 PM
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Pete,

Thanks for the reply! Any chance you could provide more details on how to bring in that third wire?
 
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Old 11-16-19, 04:23 PM
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I do it all the time. I run a new low voltage cable. Either a five or eight wire cable.
 
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Old 11-16-19, 04:31 PM
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Not having a ton of experience with electrical, am I to assume that the transformer is set up similar to a door bell transformer -- mounted to the side of my panel?

Any chance you could point me to a wiring diagram?
 
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Old 11-16-19, 04:49 PM
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I labeled the two low voltage contacts in your picture. Two wires would connect from there to R (Rh) and W on the thermostat. A separate 24vAC transformer would connect to Rc and C on the thermostat. You could use the type of transformer that mounts to an electrical box or panel...... or..... use a plug-in type wall wart. I left you a link below to a popular transformer for wifi stats.

24vAC wall wart
 
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Old 11-17-19, 06:10 AM
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Hi, what is the model # of that control? Best bet if you want LV Tstat, pull new cable to the Tstat location an 18/3 or 18/5 best to use.
Geo
 
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Old 11-17-19, 08:00 AM
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Life may be simple for herrma29. In the photo upper left corner is arrow pointing to two terminals jumper-ed with bare copper wire. Those may be T T terminals for low voltage activation of burner.

herrma29
can test this by removing jumper and measuring voltage across terminals. If it is 24 volts those are TT terminals.

To confirm this, with jumper removed, temporarily raise HI temp setting to 200F.

If burner does not start after 60 seconds then jumper terminals.

If burner starts they are TT.

Remove jumper and return HI temp to original setting.

Wire terminals to thermostat RH and W for low voltage control.
 
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Old 11-17-19, 08:50 AM
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Yes. That is exactly what I posted previously.
 
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Old 11-17-19, 06:33 PM
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My post #9 was how to confirm that connecting TT terminals activated burner before connecting it to thermostat.

Modern thermostats with many features and terminals often are improperly connected and setup. Herrma29 should start with confidence that connecting TT started burner.

Herrma29's control unit is archaic and should be junked. He could cut fuel costs by 20% and improve system operation with Out-door-reset and modern burner control.

https://www.supplyhouse.com/Tekmar-2...iler-4150000-p

https://www.supplyhouse.com/Honeywel...ic-Oil-Primary

https://s3.amazonaws.com/s3.supplyho...s/R7284Bro.pdf
 

Last edited by doughess; 11-17-19 at 07:10 PM.
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Old 11-21-19, 04:29 PM
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Thanks for the replies! I hope to get to it soon. Honestly not too familiar with this kind of work, but I would assume it makes a difference which wire goes to which screw, no?

 
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Old 11-22-19, 07:37 AM
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herrma29 Yes, the difference in terminals can result at set temperature whether burner or AC is started.

Many modern thermostats often have 3 to 5 minute delay when powered is first connected to C and RH (heat) RC (cooling) before they activate anything. When connecting or trouble shooting that delay can often confuse things.

NEXT AT THERMOSTAT before connecting wires to it, temporarily connect wires from TT. If burner starts THEN connect correct T T wires to RH/RC and C

If burner did not find start, find out why before connecting anything to thermostat.

Footnote: the thermostat delay is to protect air conditioners compressors from burn out do to frequent starts. Usually the feature cannot be disabled even if AC is not on system.
 

Last edited by doughess; 11-22-19 at 08:18 AM.
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Old 11-28-19, 01:05 PM
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Ok, so I tested the voltage between the two TT terminals and it read 28v.

I'm not quite sure how the new thermostat is supposed to control the boiler though just by wiring to the TT terminals.

The only way for me to get a reading on the terminals was if I had power to the unit. The only power in is directly controlled by the line voltage thermostat. When the thermostat is on to provide power, the unit runs, even with the jumper removed.

Am I missing something?
 
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Old 11-28-19, 03:42 PM
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If burner starts THEN connect correct T T wires to RH/RC and C
@ doug....... this is not correct.
It should be Rh and W. A thermostat requiring a C connection won't work here.
Also.... why are we discussing A/C as there is no mention of A/C.


Opening the TT terminals should not allow the circulator to operate.
Is the circulator coming on with TT open ?
What is the model of the aquastat.

When you connect a low voltage thermostat...... the line voltage one will be bypassed.
 

Last edited by PJmax; 11-28-19 at 05:25 PM.
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Old 11-28-19, 05:05 PM
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Correct. I removed the jumper and the burner still fired. The aquastat is a Honeywell L8124C

Here's a video I took of the unit: https://photos.app.goo.gl/wBsxFGjAF7hojhrb7

The wiring is configured such that, when the emergency shut-off and thermostat are closed, the burner runs, even with the jumper removed on the TT terminals. If either are open, the burner does not run.
 
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Old 11-28-19, 05:31 PM
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My mistake..... I meant to type circulator not burner. I changed my last post.
The burner is controlled by the limit switches. The thermostat starts the circulator and based on the boiler temperature.... the burner will cycle.
 
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Old 11-28-19, 06:07 PM
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So the burner will fire if within the limits, even if the thermostat isn't calling for heat? Because that seems to be how it is working.
 
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Old 11-30-19, 05:21 AM
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I believe I've answered my question. It appears most boilers are configured to keep a constant supply of hot water available -- the thermostat only triggers the circulator.

The way my boiler is wired now is abnormal. When the thermostat opens, it cuts power to the boiler entirely, allowing the water in the system to cool to ambient temperature. I assumed this was normal, as this is my only experience with a boiler and it makes sense on a level: why burn fuel to keep water warm if you're not going to be calling for heat?

I'm curious to see how efficient one way or the other is.
 
  #21  
Old 11-30-19, 04:30 PM
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That is the way hydronic systems work.

Room thermostats activate zone valves or circulator.

Boiler aquastat or out-door-reset controls water temperature. On some controls the setting is labeled “Limit” as in upper.

Out-door-reset can reduce fuel cost 20%. ODR is a standard feature on new modern boilers.

An alternative is cold start. Letting boiler cool down until next call for heat. There are many factors to determine which system to use.

https://www.supplyhouse.com/Tekmar-2...iler-4150000-p
 

Last edited by doughess; 11-30-19 at 06:15 PM.
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Old 12-02-19, 03:12 AM
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Hey Doug,

In post #12, were the two items you shared meant to be used in conjunction with one another, or is the outdoor reset a replacement for my aquastat, with additional capabilities?

My thermostat is wired up and controlling my boiler wonderfully now. Thanks, guys!
 
  #23  
Old 12-03-19, 08:10 AM
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Out-Door-Reset is replacement aquastat with a second sensor on outside wall.

The 180F boiler water temperature commonly used on USA systems is needed only on the coldest days. For most of the heating season lower more economical temperatures starting at 140F and up can be used.

For years, before installing ODR I adjusted boiler temp every month or so according to outside temp. October 140F, December 160F, January to March 180, April 160F, May 140F.

ODR's for $158 just do it more directly and save up to 20%. On a $1,000 fuel bill that is $200 every year. https://www.supplyhouse.com/Tekmar-2...iler-4150000-p

ODR's can save money in other ways. Setting shorter burner run time reduces stack temperatures and increases efficiency. I set delta-T at 5F.

Stack Losses: …..The lower the stack temperature, the more effective the heat exchanger design, and the higher the fuel-to-steam efficiency. ( From Page 6, right column bottom paragraphs)
http://cleaverbrooks.com/reference-c...cy%20Guide.pdf

Some DIY's are big on long cycles that result in higher stack temps and less efficient operation. For them Tekmar 256 ODR's have option for longer cycles. Whatever sells !?

Look at the charts on stack temperatures versus efficiency and take your choice. See Page 7 in link. (charts use net temperature, measured stack temp minus room temp)
 

Last edited by doughess; 12-03-19 at 09:46 AM.
  #24  
Old 12-06-19, 04:10 PM
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The Beckett Burner Manual chart on Efficiency vs Net Stack Temperature (Page 26) is better than one in Post 23 from Cleaverbrooks.pdf

https://www.beckettcorp.com/wp-conte...to-Oilheat.pdf

Note : Subtract room temperature from measured stack temp for “Net Stack Temp ºF.” used on chart.
 
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