To hot - Boiler Control and Thermostat CG8

Check to see if the 256 is set for the type of Terminal Unit your system uses (Terminal Unit is their way of saying the tyoe of radiator you have).

You describe "recessed fin tube" as the radiators you have. In this case you set the Tekmar 256 to BOIL DSGN to 180° and the BOIL MIN to 140°. This appears to be where you are already set. Try to adjust those numbers to BOIL DSGN 172° and BOIL MIN to 140°. See if that reduces the room temperature to 70°. This will move the curve for the coldest day to be a little cooler. it may not adjust the top of the curve (the warmest days) enough to notice.

Next try moving the BOIL MIN to 135° and see if that helps. Always wait 24 hours between adjustments to see how each change makes the room temperatures to change.

Remember to record all your settings and then record the results after at least 24 hours of operation. It sometimes takes time for all the parameters to get your temperature just right. Eventually you will get a feel for that control and how it works in your building.

to be clear, the Tekmar 256 does not have a setting number four (4) for a heat emitter type. The chart gives you the starting point for the two settings. BOIL DSGN and BOIL MIN based on that type of emitter. Your tekmar 256 is already set that way. I am suggesting that you adjust BOIL DSGN from 180° to 172° for the first step in adjusting the reset curve.

with a cast iron boiler you probably can not make the swt low enough to match the load of the building on mild or moderate days without the boiler condensing (unless you have a separate mixing system to make the system water cooler than the boiler).

you probably need a t-stat input to cycle it on warmer days.

When using the Enertrol with or without the Pin Timer, you still used the existing room thermostat to control the room temperature in the homeowners living room. That thermostat was not removed when the Enertrol was added.

You have a one zone building with 4 units that overheat. The ODR from American Stablis or Tekmar did (does) not have any provision for room sensing. That is done with a standard room thermostat placed in one of the dwelling units to sample a representative room for the entire building. That thermostat is (was) subject to tenant tampering so you may want to use a remote sensor thermostat an locate the actual control in a locked room away from tenants.

That thermostat will connect to the system the same way it would if there was no ODR at all. The ODR just connects in series with the burner limit. The thermostat connects to the control the brings on the burner and the pump to heat the rooms. If that does not make sense… ask me to explain it in more detail.

I can not be sure if this is your exact wiring diagram since I do not know if you have a WM CG-8 series 2 or series 12 or any of the other intermediate CG series boilers from WM.  But it should be close enough for this explanation.  I believe this is one that is close to the 1990s CG boilers from WM.  So let's start with the basic diagram here   

You can see how Weil McLain recommended the boiler be connected to a thermostat by looking at the purple line. It starts at 24v. transformer, then goes directly to a thermostat. From the thermostat the power continues to the relay Coil CR in the orange box. From there the power has a return path back to the 24 v. transformer. When the thermostat calls for heat and completes the circuit, the CR gets energized and closes 2 sets of contacts.   CR1 and CR2. Contacts CR2 complete the circuit from  120 v. to the circulator pump.  Contacts CR1 complete the 24 v. circuit thru all the safety limits to operate the burner. 

There are no outdoor reset devices in the original wiring recommendations from Weil McLain.  With a 4 unit building and only one zone for the entire building, I can see that overheating some rooms may become a problem.  That is why someone may have decided that outdoor reset was a good idea.

In order to add outdoor reset the control that measures the boiler temperature and the outdoor temperature must be able to turn off the burner but not turn off the circulator so that control must be set in the LIMIT circuit shown in blue.  The limit circuit has no control over the circulator so that pump can continue to operate regardless of the water temperature.  There is a limit on the diagram that is labeled “ADDITIONAL LIMIT (SEE NOTE 6)”   This is where the outdoor reset control can break the circuit to the burner without affecting the circulator operation.  

I have added the automatic vent damper end switch that proves the vent damper is completely open. Once the vent damper is completely open, that safety switch completes the circuit to the burner circuit by powering the ignition control with 24 VAC.  then the return path from 24 V. (GRD) is connected with a return path to the 24 v transformer source.   As you can clearly see in the blue line on the diagram, all the safety devices like the high limit, spill switch, vent damper end switch, and rollout fuse are all in series with the burner circuit.  If any one of the safety controls, or limits or operating controls open for any reason the burner will stop operating and that main gas valve will close.  

Now understanding the simple logic of outdoor reset will help you understand that input from the room temperature sensor may not be easily added to the equation. The outdoor reset measures the outdoor temperature with a resistance change from the outdoor sensor. The boiler temperature sensor is then measured the same way and added to the equation to determine the ideal temperature to shut off the burner.   

The equation or Logarithm calculates the two temperatures and determines at what combination of the two temperatures the limit contacts should open or close.  It is just that simple.  As one temperature increases the other temperature should decrease and at that set-point of the two temperature calculation will always equal a constant number in the reset control to open the contacts or close the contacts.  This is the simplest control for ODR.  Here is an example of how it might work.  The operator selects a desired temper combination.  It might be when the outdoor temperature is 32°F the boiler temperature needs to be 170° to heat the building properly.  If you add the twi numbers together you get 202°.   On a 1 to 1 reset curve the number must always be 202  so when the outdoor temperature increases to 52° the boiler temperature of 150° will be sufficient to heat the building.    When the outdoor temperature reaches 62° the boiler temperature will drop to 140° and the reset control will open the contacts to stop the burner.  

As you can see, a 1 to 1 ratio may not be ideal so the reset curve may need to be adjusted to a 1.5 to 1 ratio or a 2 to 1 ratio depending on the conditions at that particular location.   That is all the Takmar 256 does.  You get to select the reset ratio and the start and stop boiler temperature based on the outdoor temperature.  

Adding the room temperature to this algorithm is doable but that control now becomes more expensive because you need the logic of the control to prioritize the room temperature over the other two temperature inputs.  In your case you can just put the indoor temperature sensor in one of the rooms and connect it to a standard thermostat that can turn the circulator pump on and off, as shown in the following diagram.  

here is an inexpensive room thermostat that can use a remote sensor ICM thermostat you will need to purchase the optional outdoor sensor and connect it this way: ICM remote sensor

I hope this helps

I don't believe you need the Tekmar 260. What you have will do the job

Your diagram is very similar to the one I used.

I get the feeling the Tekmar does use the 'Demand Input' for its algorithm. Although IMO Tekmar does a very poor job of explaining the overall use of the 'Demand Input'. Since the indoor temperature is what determines the demand. In this case it is the only way the Tekmar 256 can monitor indoor temperature.

If this was my system I'd add a relay that has 2 independent output contacts, so the thermostat controls the overall use of the boiler (the boiler's thermostat connection) and the 'Demand Input' to the Tekmar 256. The Tekmar 256's boiler contacts will control the boiler's burner as described above.

More info here;

https://www.watts.com/our-story/brands/tekmar/references/essays