Please help a noob set up a Tekmar 256 to my boiler

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Old 12-29-12, 08:42 PM
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Please help a noob set up a Tekmar 256 to my boiler

Hey everyone. I have some questions about wiring up a Tekmar 256 outdoor reset controller to my boiler. Although I do a lot of projects myself, this is my first real experience with the heating system. My goal is to try to improve the efficency of this old boiler without making drastic changes. I'm hoping that running the boiler a little cooler will help with that.

My system is pretty old and seems pretty basic. I have a gas-fired boiler with a single zone. No AC. The house has cast iron radiators on the second floor and baseboard radiators on the first floor.

Before I touched anything, I made a diagram of how everything is set up now:



Here are pictures of the components/connections:

Temp controller (set at 180*):



Boiler:



Gas Valve Connections:





Relay Box Controller Thingy (& Inside Cover):





Connections on Tekmar Controller:



From reading the Tekmar's manual, it seems like terminals 5 and 6 got to the TT terminals on the relay box, 7 and 9 got to my thermostat, and 8/9 go to the transformer.

Like this:



Assuming that's correct (and I don't pretend that it is), how does the boiler get connected? Also, what, if anything, gets connected to 5/6 on the relay box? Finally, does the temp sensor get eliminated by the Tekmar? I would think so, but just want to confirm.

Thanks in advance for any help you can lend.

Patrick
 
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Old 12-29-12, 09:03 PM
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it seems like terminals 5 and 6 got to the TT terminals on the relay box
You said this and then asked how the boiler gets connected ?
You answered your own question.

The input sensor gets mounted to the copper supply line pipe. Next to existing temp sensor.

In the Tekmar product description I see the following:
Microprocessor control. This is not a safety (limit) control
I think I would leave that temp sensor just where it is as a safety shutdown.

Wait for the replies from the regulars too.

P.S. Nice diagrams
 
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Old 12-29-12, 09:15 PM
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I understand that it seems obvious that "Boiler" on the tekmar would go to the boiler, but that's not how the instructions show it. The instructions show that 5/6 on the Tekmar go to the TT terminals, and not the boiler.

I'll see if I can find an electronic version and post them.

EDIT: Here's a link with the instruction manual. Page 14 shows 5/6 going to the TT terminals. (Maybe someone can even tell me what "TT" stands for!)

http://www.tekmarcontrols.com/images...e/256_d_07.pdf

Also, I should have been a little clearer on my first post - I'm fine with the sensor connectors (outdoor and water temp). But does that mean I leave the current temp sensor hooked up as-is? I think the Tekmar also has a MAX temp for the boiler.

As for the diagrams - my wife called me a dork when I was making them, so I knew I was on the right track!
 

Last edited by BaltPatrick; 12-29-12 at 09:23 PM. Reason: Added link to manual
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Old 12-29-12, 09:26 PM
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my wife called me a dork
Jeeze, where have I heard that before?

Patrick, it's going to take some time to get you straight on this, but it's gettin' late and I gotta go sleepy...

I'll get back with ya on the morrow...
 
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Old 12-29-12, 09:27 PM
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(Maybe someone can even tell me what "TT" stands for!)
T T stands for "Thermostat" connections, but your old berler won't have them called exactly that.

Just looked again, you aren't gonna let me get outta here that easy, are you?

The T T connections are on the 845 Honeywell relay box, that's where the Tekmar wires will go.

You are going to leave the temp control (your HIGH LIMIT) control (the PENN box) connected... along with the wires to 5 and 6 in the 845... and the wires on the gas valve obviously need to stay.

I normally draw up schematics for situations like this but my computer crashed the other day and I can't find the install disks for my CAD program... so I hope I can describe it to you, then you draw it and I'll check it... deal?
 
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Old 12-29-12, 09:28 PM
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Thanks man. I appreciate any help you can lend.
 
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Old 12-29-12, 09:32 PM
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Goodnight Troop.......




Yes....the Tekmar does have the ability to control max temp but it says it's not a safety.
I'll leave this in Troopers hands. He'll fill you in....in the AM.
 
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Old 12-29-12, 09:34 PM
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night PJ!.................
 
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Old 12-29-12, 09:39 PM
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OK, last one...

actually, on second look, you've got the wiring of the 256 correct,

but you need to leave all that other wiring the way it is...

we'll talk more about the settings and stuff tomorrow...

this time I'm really leaving!
 
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Old 12-30-12, 07:10 AM
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One aside question here...just how do you make those diagrams??
 
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Old 12-30-12, 07:43 AM
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I used Microsoft Paint and a lot of patience. The only "problem" I found is that you can't draw white wires on a whire background.

I'm much more of a visual person, so I knew I would be lost without pictures and a decent diagram.
 
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Old 12-30-12, 09:32 AM
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OK, I looked again at the diagram, before and after, and yes, the Tekmar wiring is in fact correct, and yes, you leave the wiring on 5 & 6 , and to the gas valve, and to the PENN (high limit) control, and to the transformer.

So basically what you are going to do as per your drawing is

ADD connections to the existing connections on the transformer to power the 256 (24VAC)

MOVE the thermostat from the 845 to the 256

ADD connections from the 256 to the T T on the 845

=========================================

Here's the thing that you need most to understand about using ODR on a CONVENTIONAL, "NON-CONDENSING" boiler:

You must NOT set the BOIL MIN below 150, and I would personally be a bit leary about going below 160 with your system.

Much has been written here about FLUE GAS CONDENSATION which can severely damage and destroy boilers, flue pipes, and chimneys. It's all about the 'dew point' of the flue gases and with an GAS fired system that 'dew point' is around 135F. When the flue gases contact a surface that is LESS than the dew point, the water vapor in the gases condenses on that surface. That condensate is ACIDIC and if allowed to persist in the liquid state will EAT any metal it comes in contact with.

The dew point at 135-ish... you ask why set BOIL MIN so much higher?

Because the 150-160 setting is the SUPPLY, the HOT out of the boiler, where your temp sensor for the TEKMAR will be placed. The COOLER RETURN water will be at LEAST 20F cooler and this will flow into the boiler and cool the cast iron. If you get a high flow of too cool water back into the boiler, the gases will condense on those fire side surfaces inside.

So you have to compensate for the "DELTA T" (difference in temp) between the supply and the return.

This limits the amount of savings ODR allows with a CONVENTIONAL boiler, a sad fact of life. You don't want to save $50 in fuel only to destroy your boiler system (which looks in REALLY great shape for it's age!... unlike me!)


The house has cast iron radiators on the second floor and baseboard radiators on the first floor.
Mixing cast iron rads and fin-tube baseboard on a single system can be problematic.

Let me ask first though... is the baseboard upstairs a copper tube inside with aluminum fins?
OR, is it CAST IRON BASEBOARD?

The reason it can become a problem is because when the cast iron rads get hot, they retain the heat and slowly radiate it into the space, whereas the low mass fin-tube baseboard heats and cools VERY quickly in comparison.

The downstairs will probably remain warmer, longer, which would result in the boiler not being called on for heat, while the upstairs will cool and may become too cool for comfort.

more later, I'll let you 'digest' your breakfast...
 

Last edited by NJT; 12-30-12 at 03:37 PM.
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Old 12-30-12, 09:35 AM
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OK... I can't let it go...

Looking at the boiler pic, it appears that you have separate runs on the supply and return from both the up and down stairs heating loops. It would be fairly easy to zone that system with electric zone valves to remedy any problems that you might discover with heating balance between the up and down. A thermostat wire would have to be pulled, but the rest of the work would be at the boiler and accessible. Something to put on your Cheerios.
 
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Old 12-30-12, 09:38 AM
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Last thing for now...

I would like you to read both of these 'sticky' posts. I'm CERTAIN that your expansion tank air charge needs to be maintained...

In this first one are step by step instructions for checking and charging the expansion tank (the red tank to the left of your boiler). It talks about the relief valve leaking... and even though yours may not be at this point in time, if you don't maintain the air charge in the tank, it WILL, sooner or later. Be proactive and prevent that.

http://www.doityourself.com/forum/bo...sion-tank.html

This one's title is self-explanatory:

http://www.doityourself.com/forum/bo...ure-gauge.html
 
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Old 12-30-12, 10:47 AM
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Thanks Troop - You've given me a lot to digest. I'm going to look over what you wrote and post up a new diagram tomorrow. (I have to take a break to hang out with my mother-in-law, or my aforesaid wife will be calling me things worse than "dork!")

Thanks again!

Patrick

BTW, the first floor is copper tubing baseboard w/ aluminum fins, not cast iron.

When you talk about condension, you gave a temp for oil-fired systems. Is it the same for gas?

Also, I had a boiler service done when I brought the house in 2010, and they charged up my expansion tank with what looked like a little CO2 cartridge. Anyway, I'll try to write more soon. Thanks.
 

Last edited by BaltPatrick; 12-30-12 at 10:51 AM. Reason: Add'l info
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Old 12-30-12, 03:42 PM
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you gave a temp for oil-fired systems. Is it the same for gas?
Oooops, my bad, good catch. I edited my post.

GAS is around 135, and OIL is said to be around 115-120, depending on who you believe, but I suspect that oil is more like 125.

they charged up my expansion tank with what looked like a little CO2 cartridge.
It might have been nitrogen. Just as they are putting nitrogen in car tires these days, so are some guys using nitrogen in expansion tanks. Commercial installations often use nitrogen in the big steel compression tanks.

Happy New Year!
 
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Old 12-30-12, 05:11 PM
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I had always assumed that nitrogen gas, with a molecular weight of 28, would be slower to diffuse through a rubber tank bladder (or tire) than air. But i just looked it up, and air has an average molecular weight of 29: Molecular Weight - Gases and Vapors

Since air is about 80% nitrogen, then the other gaseous components of air must be heavier than nitrogen. So why is nitrogen being used to fill tires or bladder-type expansion tanks? For tires, I understand that there is an extra charge for nitrogen filling? Nitrogen is essentially inert, so that would reduce corrosion of metals.

Maybe the repairman was, in fact, using CO2, which as a molecular weight of 44, which should reduce diffusion through rubber.
 
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Old 12-30-12, 07:46 PM
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I think the N2 in car tires is probably the gas industry trying to make money. I don't buy into the claims that it's 'better'. Race cars use nitrogen, airplanes use nitrogen, but it's because they don't want the associated water vapor introduced into the tires. My truck wheels aren't corroded on the inside... the rubber doesn't oxidize on the inside faster than I can wear out the outside. No, to me, I find the extra charge for N2 in a car tire ludicrous.

I believe that you are correct that it will diffuse through the membrane FASTER than regular old air.

In a STEEL compression tank though, using N2 makes sense because of the fact that N2 is not an oxidizer as O2 is. It should drastically reduce if not eliminate corrosion inside the tank... but is that an issue? Ask your 60 year old tank!

Maybe carrying a CO2 cartridge to fill expansion tanks is easier than lugging an air compressor? And definitely easier than using a hand pump!
 
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Old 12-31-12, 02:20 PM
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Ok, thanks again for all of the suggestions. I made up a new diagram.



Assuming this is correct, then I have a few more questions:

1) Do I need the Penn temp sensor? I'm leaning towards eliminating it if possible for 2 reasons - 1 general decluttering and 2, I don't want any conflicting signals between it and the Tekmar.

2) Can anyone describe the "thought" process of my boiler with this hookup? For example, ​my understanding​ is thatunder the old system, the thermostat called for heat, the relay turned on the circulator pump and gave the boiler permission to fire. If the temp sensor read under 180*, it closed the circuit allowing the boiler to fire.

Having an explanation like this helps me visualize what's going on. What I'm specifically concerned with is if the thermostat calls for heat, the Tekmar decides that the water temp is already warm enough so it doesn't fire the boiler. Will the pump still circulate until the thermostat is satisfied?

3) Sounds silly, but is there a reason why all of these connections use wire nuts? My DC experience is to use solderless or solder connections with heat shrink wrap. Any reason I can't use that for all of these splices?

4) What is the squiggle (middle) terminal on my gas valve? My DC experience shows this is they symbol for a resistive load. Does it simply act as the neutral terminal?

About the expansion tank, I should be clear that I don't actually know what it's charged with - just that it LOOKED like a CO2 cartridge. How often should that tank be inspected?

Anyway - Thanks again everyone!

Patrick
 
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Old 12-31-12, 05:21 PM
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1) Do I need the Penn temp sensor?
YES! you ABSOLUTELY DO NEED IT! It is a primary SAFETY CONTROL! Without that control in place the boiler could heat up to whatever temp it wanted to. The Tekmar is NOT a primary safety control. You MUST leave the Penn control in place!

What I'm specifically concerned with is if the thermostat calls for heat, the Tekmar decides that the water temp is already warm enough so it doesn't fire the boiler. Will the pump still circulate until the thermostat is satisfied?
Oh crap... you're correct! I forgot all about the circ won't run! Time for plan B.

I did find the disks for my CAD program... I'll draw something up for you.

Any reason I can't use that for all of these splices?
Makes it that much more difficult to change components when they fail. There's nothing wrong with wire nuts. There MAY be something in the National Electric Code about that... and remember, none of this wiring is DC. It's all AC.

4) What is the squiggle (middle) terminal on my gas valve? My DC experience shows this is they symbol for a resistive load. Does it simply act as the neutral terminal?
The 'squiggle' is showing that the connections to the SOLENOID COIL that opens the valve are on the TH and TR terminals. The center terminal has NO CONNECTION inside the valve, it is there as a convenient point to make the connection between the THERMOSTAT (TH) and the TRANSFORMER (TR).

A squiggle is not the symbol for a resistor. Resistor symbol is like a sawtooth. What you are seeing there is the symbol for an INDUCTOR, which a solenoid coil IS.

How often should that tank be inspected?
The air charge should be checked and adjusted at a MINIMUM of every two years. YEARLY is better. Read this again:

http://www.doityourself.com/forum/bo...sion-tank.html
 
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Old 12-31-12, 05:37 PM
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Soldered 120-V splices are not ever approved by the National Electric Code - wire nuts are, but they must be inside a UL-approved electrical box (not dangling in mid-air). For 24-V control wiring, there is more flexibiity.
 
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Old 12-31-12, 06:24 PM
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Hey Troop, thanks for the feedback. I looked at the thread on the expansion tank, and once I get this project squared away, I'll turn my attention to that.

If I leave the Penn sensor connected, should I leave the temp setting at 180*, or can I lower to something else?

If the circulator pump isn't running, I suppose the system would still work, but then only by gravity. If there's a way to get the pump working independent of the boiler, I'm all ears.

Gilmorrie - Thanks for the info too. I didn't plan to solder any of these connections, but I was going use the solderless crimp connectors. As you can see in some of my pics, all I have are wire nuts dangling mid air. The wiring is a patch on top of patch - some of the wire is really ancient looking with cloth insulation.

Once I get the final wire diagram done, I planned to replace all of this old stuff, but use the crimp connectors w/heatshrink. I'm not too worried about constantly undoing connections - the next likely time for that is when this whole kit-n-kaboodle gets replaced, so wire connections will be the least of my problems.

Troop (or anyone else) - thanks for helping me with this diagram. I hope this not only can help me, but other people who are setting up something like this. I'm trying to be meticulous with the diagrams and pics so people like me can use this information in the future.

Happy New Year everyone!!

Patrick
 
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Old 12-31-12, 08:44 PM
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should I leave the temp setting at 180*, or can I lower to something else?
Yes. Leave it at 180. The ODR will control the temperature, but it may need to fire to 180 in the coldest of winter and if you turn the PENN down, it won't be able to.

Here's how you need to wire it up:



Thermostat calls for heat, activates 845 relay.

845 relay turns on circ pump, AND CLOSES CONTACT AT 5 & 6.

5 & 6 then in turn send demand to 256.

256 powers gas valve through high limit switch.
 
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Last edited by NJT; 12-31-12 at 09:27 PM.
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Old 12-31-12, 09:04 PM
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Awesome Troop. Gracias!

I confess I stared at your drawing for about 10 min trying to mentally follow the circuits, but it makes sense to me now.

I'll post up with my results. Thanks again everyone!
 
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Old 12-31-12, 09:08 PM
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Patrick, I put a revision up just now that will make it easier to wire with 2 wire thermostat wire all around.

2 wires from transformer to 256, 2 wires from 256 to gas valve, 2 wires from 256 to 845, 2 wires from gas valve to high limit control.

Happy New Year!
 
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Old 12-31-12, 09:17 PM
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Thanks again, but I can't see the revised diagram. I just see a little blue question mark.
 
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Old 12-31-12, 09:22 PM
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Hit refresh, try it again, I think I messed up.... not unlikely!
 
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Old 12-31-12, 09:31 PM
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It's working now. Thanks!
 
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Old 01-01-13, 01:59 PM
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One last pointer Patrick, I think you know this already, but just in case:

When you install the sensor on the boiler SUPPLY out pipe, try to get it as close to the boiler as possible and insulate the pipe around the sensor and to each side, at least 12". This will make the sensor as responsive and accurate as possible.
 
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Old 01-07-13, 04:31 PM
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Earlier in this thread, there was discussion about pressurizing bladder-type expansion tanks with nitrogen instead of air.

I accidently ran across this 5-year-old posting by rbeck:

Also to add a fact about the bladder type tanks. The bladder is oxygen permeable so the oxygen ends up in the system. That is why many tank manufacturers have gone to charging with nitrogen, plus nitrogen is way more stable with temperature changes.
 
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Old 01-07-13, 08:51 PM
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So, even if the N2 is a smaller molecule and permeates through the membrane faster, it's not corrosive O2 that's getting into the system...

yes, we knew about the greater temp stability, but again, that's because of the water content. N2 from a can is DRY gas. I don't believe that O2 is any softer or harder than 02 as far as compressibility goes. Add water vapor to the equation and along with it comes temperature instability.
 
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Old 01-08-13, 09:49 AM
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Just a bit of an update:

I've got everything wired up the way Troop has it diagramed in Post#23 and everything seems to be working as designed. When there's a call for heat, the circulator pump turns on, and if necesssary the boiler fires a short time later. The Tekmar went through a quick setup; I started out with the values that were already programmed in there. I think it set the boiler design at 160* and the Boiler Min at 140*. I set the outdoor design with the factory setting of 10*. I left the Penn box at 180*, but based on the Tekmar's settings, it should never get there.

It's too early to tell if everything's exactly the way it should be, but no problems so far. We keep the heat around 66* and we've been comfortable in the house. I haven't been running down to the basement however to see what temp the Tekmar has the boiler at, and it'll take at least a month or so to know if there's been any impact on my gas bill. The outside temps have been in the high 30s/low 40s. I also took the opportunity to remove some of that ancient wiring that was hooked up to the boiler (some had cloth insulation) and re-wrire everything with new wire. (I wondered why the last person used so much electrical tape instead of wire ties, then I realized that plastic wire ties might not have been available the last time this thing was rewired!)

As for the temperature sensor, I placed it as close to the boiler's output as I practically could. Immediately out of the boiler is a large (maybe 2 1/2") cast iron pipe, which transitions into smaller copper to go to the expansion tank. I put the sensor on the copper thinking that the copper would give a better and more responsive heat transfer, and it would be easier to get insulation around the smaller pipe than the giant cast iron one. I can post up pics when I get home, but in my boiler pic above, you can just make out a piece of the cast iron sticking out from behind the boiler. The sensor is mounted just to the right of the expansion tank. I didn't have a 12" section to insulate (it was about 6"), but it's the whole pipe segment between the cast iron and the expansion tank.

My next project will be checking the expansion tank, and then putting some better weatherstripping around my doors.

Thanks again for everything.

Patrick
 
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Old 01-08-13, 03:16 PM
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Everything sounds fine Patrick, but I might set the BOIL DESIGN up to 175-180 or so. You might need that extra range when it gets cold out. It won't go there unless it needs to.

Good Luck and let us know of any perceived savings (or problems, hopefully none!)
 
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Old 01-13-13, 11:32 AM
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Trooper

Hey there Trooper, I was just looking at your diagram, pretty neat. Isn't terminal 7 supposed to be common.

Nut
 
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Old 01-13-13, 04:05 PM
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Hi Nut, thanks...

Term 7 is one side of the relay in the Tek...

it is being switched to common when term 5 & 6 on the 845 relay box 'make' during a heat call.
 
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