# Boiler outdoor reset control



## COLDIRON (Mar 15, 2009)

Most commercial and industrial buildings that use hot water for their air handler hot water coils have what is called a reset schedule with outside thermometers that changes the hot water temperatures according to outside ambient air temperature.

Example: Not true figures just an example . 

Outside air Temp Hot water temp

55 & above 130 & lower

45 140

35 150

25 160

15 170

5  180

I have not seen this in residential housing but I am sure someone has it somewhere.


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## liquidplumber (Dec 31, 2009)

*Reset*

Outdoor reset is doable on that boiler but, whether or not it is worth doing depends on many things.

What do you use for domestic hot water?
What type of heat emitters do you have?
What is age of house?
There are many other factors but this will be a start.


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## beenthere (Oct 11, 2008)

Outdoor reset is very common on residential systems.

Do you have a tankless coil in your boiler.
If not. You can use outdoor reset.

Savings of 15% or more are possible. Depending on your areas winter conditions.


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## Joe F (Jan 27, 2008)

I don't have a tankless coil, my hot water comes from a basic stand alone gas water heater. If I remember correctly, the high limit on my boiler is set manually by a "thumb wheel", would that wind up being replaced? Any good references I should look at to get familiar?


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## beenthere (Oct 11, 2008)

No, the limit control stays the same. And set the same. The outdoor reset is wired in series with the aquastat.


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## liquidplumber (Dec 31, 2009)

*Try this*



Joe F said:


> Any good references I should look at to get familiar?


http://lmgtfy.com/?q=outdoor+reset


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## tk03 (Sep 30, 2008)

The best way to do outdoor reset on that boiler is system reset not boiler rest. It will reset the system but let the boiler run up to whatever temperature it needs to.
More reset info.
Look down the right column and click on Outdoor reset.
http://www.comfort-calc.net/tech_area_index.htm#HWB


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## COLDIRON (Mar 15, 2009)

beenthere said:


> Outdoor reset is very common on residential systems.
> 
> Do you have a tankless coil in your boiler.
> If not. You can use outdoor reset.
> ...


Not Really that common.:no:


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## beenthere (Oct 11, 2008)

SULTINI said:


> Not Really that common.:no:


Maybe not in philly.

But around here. Very few new boilers go in. That don't have outdoor reset installed with them. Weather as standard with the boiler, or as an add on option.

Weil McLain Ultra, it comes with the boiler as standard(both oil and gas version of the boiler).

Buderus, it comes with the Logamatic control(both oil and gas version of the boiler).
Along with some other brands.

Most residential mod/con boilers now come with outdoor reset as standard. Those that don't recommend it. And its sold as an add on upgrade.

At least half of my boiler sales have outdoor reset.
And my competition is offering it also. So they're seeing the same trend as me. People want to save money. And are willing to pay a little extra up front to do so.

What residential mod/con are you selling that doesn't have it.

And is there a reason you don't offer it as an upgrade to new boiler sales/swap outs of non condensing boilers. Or as an energy saving upgrade/add on to customers for their current boiler.


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## Scuba_Dave (Jan 16, 2009)

So a reset replaces the controller/aquastat...I see prices of $350 or so....
I have a Honeywell controller, circuit board stamped 8805
I'm going to be replacing the boiler (23 years old - not in great shape)
So I'm thinking its better to just wait & have one installed with the new boiler

I've adjusted my Hi-limit temp down
Once the weather warms up I'll turn it down more for the Spring


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## Joe F (Jan 27, 2008)

tk03 said:


> The best way to do outdoor reset on that boiler is system reset not boiler rest.


What's the difference?


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## H. Phillips (Jan 5, 2010)

I think many of the older boilers did not like running at a lower water temp. I think they were prone to cracking at lower temps, not sure. If running fuel with high sulfur lower temps can cause the sulfur to react with the moisture and other exhaust gases and condense out as sulfuric acid which would corrode (rust out) the boiler. Not commonly a problem with the more refined fuels used in housing. So for those boilers you would use a mixing valve to temper the water temp down by mixing the boiler water with some return water, that way the boiler runs at its maximum water temp all the time. The disadvantage is that the boiler should have higher efficiency at the lower water temp so you would not gain that efficiency.

Read the manufactures instructions, the should list a minimum operating temp if there is one.


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## beenthere (Oct 11, 2008)

Scuba_Dave said:


> So a reset replaces the controller/aquastat...I see prices of $350 or so....



NO.

It doesn't replace the controller/aquastat. It is installed in series with the controller/aquastat.

Outdoor resets controls are NOT safety controls like a aquastat is.
So if you had one installed on your current boiler. It would be reused on your new boiler.


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## COLDIRON (Mar 15, 2009)

The only thing a reset controller does is change set points on water circulation temperatures other than that the boiler operates just as it would with thermostat controls and safety controls unchanged.

If it gets real cold outside the water temperature gets hotter if it gets hotter outside the water temperature goes down.

It just gives you control over the water temperature, it's not a constant.


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## Joe F (Jan 27, 2008)

Is there a particular brand/model I should take a look at? I looked at a Taco 700 series thinking it would hook up to my ZVC, but I don't think they're compatible (I have 1 pump and 4 zone valves vice multiple pumps).


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## beenthere (Oct 11, 2008)

The PC700 works with single circulators.
Is your ZV panel, an EXP panel.


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## Joe F (Jan 27, 2008)

Hey beenthere,

I'm assuming EXP means it has an expansion slot. I pulled the cover and didn't see an expansion receptacle and "EXP" is not part of the model number of the one I have.

Edit: OK, I just looked and I see that there is a ZVC404-2 and a ZVC-EXP-1. So, it appears that I would need to get the EXP model to use the PC700. Might have to swap that out this summer...


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## beenthere (Oct 11, 2008)

Or use a different outdoor reset control.


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## Joe F (Jan 27, 2008)

beenthere said:


> Or use a different outdoor reset control.


 
Is there one in particular that you like?


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## beenthere (Oct 11, 2008)

I prefer the Weil McLain BCP.
But use the Tekmar at times also. Both are good reset controls.


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## Joe F (Jan 27, 2008)

I just took a look at the Tekmar 256 Reset Control. It appears that it would get wired between the ZVC and the boiler. ZVC end switch connects to the 256 boiler demand and the 256 TT terminals wire to the boiler TT terminals (does that sound right?).

So, if that's the case, I don't think I understand how the reset control works to control the boiler water temp. When the boiler gets a demand signal, it starts the pump and fires the boiler, water temp is set by an internal boiler circuit. No? How does a simple open/closed 2 wire signal remove the demand signal for fire, but keep the pump running?


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## beenthere (Oct 11, 2008)

The Tekmar monitors boiler temp. And will drop the call for heat to the boiler when the water temp reaches the reset temp the Tekmar determines is correct.


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## Joe F (Jan 27, 2008)

beenthere said:


> The Tekmar monitors boiler temp. And will drop the call for heat to the boiler when the water temp reaches the reset temp the Tekmar determines is correct.


But then won't the pump quit running too?


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## beenthere (Oct 11, 2008)

Is your ZVC panel controlling the circ. or is teh boilers aquastat.


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## NHMaster (Dec 21, 2009)

You can use the Taco PC700 without having to have the zone control relay (sr or ZR series)

Tekmar makes the PC700 for taco.


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## Joe F (Jan 27, 2008)

beenthere said:


> Is your ZVC panel controlling the circ. or is teh boilers aquastat.


The end switch from the ZVC is connected to the boiler (I believe boiler TT). If my system understanding is correct, that would mean that the boiler aquastat is controlling the circ.


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## beenthere (Oct 11, 2008)

Circ just needs rewired to the ZVC to control it then.

Where there is a will there is a way.


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## Joe F (Jan 27, 2008)

OK. I'll take a look at the wiring schematic in the boiler manual tonight. Maybe I'll post a picture of the actual wiring. Thanks


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## Joe F (Jan 27, 2008)

Well, from what I see, there are 5 terminals:

W G Y R C 

The end switch from the ZVC connects to G & R. W has nothing connected to it. G has a blue wire. Y has a yellow and an orange that looks like it goes to the aquastat. C has 2 yellows and R has a red and a dark blue. 

I looked at the manual, but I didn't do too well in determining what each wire is supposed to do, so I added a picture.


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## beenthere (Oct 11, 2008)

All of those are low voltage wires.

The line voltage wires for your circ. Are inside the junction box that control is mounted on.


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## NHMaster (Dec 21, 2009)

www.taco-hvac.com has all the wiring diagrams for their stuff

www.tekmar.com has the same thing

honeywell's site also


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## Joe F (Jan 27, 2008)

beenthere said:


> All of those are low voltage wires.
> 
> The line voltage wires for your circ. Are inside the junction box that control is mounted on.


I understand that I have line voltage being controlled by low voltage. Does the circ pump wiring need to be separated? I don't see a provision on my ZVC for line voltage control. Only line voltage on the ZVC appears to be the power supply to the unit.


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## beenthere (Oct 11, 2008)

Yes. the line voltage of teh circ has to be removed from the relay of the boiler.

On your ZVC. You should have main end switch, extra end switch.

Use the main end switch to control circ. And the second end switch to operate boiler.

Or. if you use the Weil McLain BCP, or Tekmar.
The main end switch tells the BCP, or Tekmar it has a heat call. And the BCP or Tekmar turns on the circ and boiler.

Witch control are you going to use. Its easier if we only talk about one outdoor reset control for wiring.


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## Joe F (Jan 27, 2008)

When I remove the circ from the boiler relay, I'll need to add a pump relay (SR501) into the system correct? As far as wiring, I'm looking at the Tekmar D256. If I'm reading the schematic correctly:

ZVC Main end switch connects to the Tekmar (boiler demand). Tekmar goes out to the boiler.
ZVC second end switch connects to the circ relay (SR510) and then line voltage out from the 501 to the pump.


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## VelvetFoot (Mar 9, 2009)

I am totally no expert. Maybe you are making this more complicated than it is. I just recently added a 256 to an Argo-controlled boiler. My case was more complicated because I wanted to use priority for the domestic hot water and had to add a relay. I downloaded the picture below from the web and have no connection or approval or whatever from the originator, but it helped me.


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## Joe F (Jan 27, 2008)

VelvetFoot said:


> Maybe you are making this more complicated than it is. I just recently added a 256 to an Argo-controlled boiler. My case was more complicated because I wanted to use priority for the domestic hot water and had to add a relay. I downloaded the picture below from the web and have no connection or approval or whatever from the originator, but it helped me.


I'm sure I'm making it more complicated than it is :huh:.


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## beenthere (Oct 11, 2008)

Joe F said:


> When I remove the circ from the boiler relay, I'll need to add a pump relay (SR501) into the system correct? As far as wiring, I'm looking at the Tekmar D256. If I'm reading the schematic correctly:
> 
> ZVC Main end switch connects to the Tekmar (boiler demand). Tekmar goes out to the boiler.
> ZVC second end switch connects to the circ relay (SR510) and then line voltage out from the 501 to the pump.


No you wouldn't have to, the outdoor reset control has its own built in relay for that.

But. My head is in left field this week.

All you have to do with the reset control is have it break the orange wire from the relay center on your boiler to your high limit on your boiler. That will shut the burner down, but allow the circ to stay running.


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## Joe F (Jan 27, 2008)

The second end switch from the ZVC would be the input to the reset control?


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## beenthere (Oct 11, 2008)

Yes. That will tell it that there is a heat call.


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## Joe F (Jan 27, 2008)

Thanks!! My wife will be so excited to see me tearing into the heating system again!

I'll let you know how it goes.


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## tk03 (Sep 30, 2008)

Sure would have been easier to do the Taco ZVC-EXP control and just plug in the Taco PC700 OD reset control to the ZVC panel.


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## Joe F (Jan 27, 2008)

I agree it would be simpler. I came up withh a cost difference of $300 between the Tekmar 256 and the ZVC/PC700 combo. I'd also wind up replacing a 1 year old ZVC-404 with a ZVC-404-EXP. Kinda hard for me to justify.


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## Scuba_Dave (Jan 16, 2009)

Found this chart as an example of reset control Temps
Not sure if it is accurate at all


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## secutanudu (Mar 15, 2009)

I read this thread and still don't understand how an outdoor reset can lower the temperature of your boiler water...if the aquastat is set for 160/180....how does the reset prevent it from turning on when the water drops 1o 160? 

Maybe this is a related question....why is it called a "reset"?


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## tk03 (Sep 30, 2008)

Your boiler should not run until there is a demand than stop when the demand from the Tekmar ends. If your control does not maintain temperature all the control of the boiler is from the Tekmar. The Tekmar demand or no demand id from the thermostat. The Tekmar will control the water temperature from the heating curve which is determined by the settings for OD air high and low and boiler water temp high and low.


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## secutanudu (Mar 15, 2009)

Sorry....having a little trouble understanding what that all means...


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## beenthere (Oct 11, 2008)

An outdoor reset is wired in series with your boiler controls, temp control circuit.
So that it can stop the call to the burner, so the burner only runs if the outdoor reset circuit is closed.

Its call an outdoor reset. Because it "resets" the boilers temp(high limit temp) by the outdoor temp.


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## secutanudu (Mar 15, 2009)

Oh, so it goes between the aquastat and the burner? 

It must have two thermostats, right? One inside on the boiler and one outside?


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## beenthere (Oct 11, 2008)

Yes, it has 2 temp sensors.

Depends on aquastat and burner as to how its wired in.


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## secutanudu (Mar 15, 2009)

Great, I understand now. Is this something I could easily install myself? I am familiar with electrical work, not boilers so much.

I have an oil-fired Weil McLain boiler from about '94.


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## beenthere (Oct 11, 2008)

There not hard to install and set up.

Just don't make a mistake and wire it that it bypasses the boilers aquastat's high limit.

MUST be in series.


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## NHMaster (Dec 21, 2009)

Both Tekmar's and Taco's web sites have the wiring diagrams for just about every situation you could come up with. BTW, Tekmar manufactures the same control for Taco. There are other makers out there as well like the Beckett Heat manager.


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## beenthere (Oct 11, 2008)

NHMaster said:


> There are other makers out there as well like the Beckett Heat manager.



Which is a joke. And a knock off of other manufacturers control scheme.

Beckett even admits. that at a bout 20° outdoor temp, the HM doesn't do anything to save you money.


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## Scuba_Dave (Jan 16, 2009)

Hey !!
Now it makes sense to me too :laughing:
I'm probably going to wait until we get a new heating system installed
Until then I will reset manually once (if) it warms up here


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## NHMaster (Dec 21, 2009)

what you want is a Buderus boiler with the logamatic control.


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