Tekmar 356 question

Looks like the Boiler Supply / Boiler Return, Mixing and the Outdoor Reset Sensors have the same resistance properties.

so this light bar graph never lights or shows any movement?

if you had a spare tekmar sensor you could wire it to #2&3 and put an ice cube on it. Or an ice cube on the outdoor sensor. The actual sensor is under the white cover.

That would tell the control to ramp up the pump speed.

One way that you test sensors is a glass of ice water, and a cup of boiling water, two known or close temperatures, then look for 32 and 212 degrees resistance readings.

But it is easy enough to check all the sensors resistance., right on the control. You will need to know the temperature at the sensor to see if it matches the resistance.

Remove the leads from the control to measure the resistance of the sensors

If I was a Tech that wanted to verify the operation of the Tekmar and other like controllers I would have a 100,000 Ohm 10-Turn Potentiometer (-5 degrees to over 383 degrees simulation) and/or a resistor decade box I could substitute for the sensor(s).

That control usually tells you if and what is wrong via error codes on the screen.

If you are not seeing error codes, test the sensors for resistance, and scroll thru settings.

The small DIP (toggle) switch left of the terminal strip is easy to miss, make sure you are in advanced to change settings. The chart below shows what screens are available in Advanced/ Installer mode. Adjust appears in the upper right screen in advanced mode

It only needs a few pieces of info to start working, the manual walks you through typical settings and how to apply them. Basically outdoor temperature for when it starts thinking, 68- 70 typically then the temperature you want to maintain at the system sensor location.

If you don't have original design numbers just pick something, like 0° for a design day temperature, 70 for design indoor temperature. The control then calculates and displays mx target, after the boiler fires it

After that lights and icons tell you what the control is doing.

If you can, take a spare sensor the 082 is a universal sensor it can be used anywhere.

If you have a spare circulator wire it to the control, hold the pump in your hand and you will feel it ramp up as the % lights come on. If you press the test button the pump will ramp up regardless of what the sensors are telling it to do. If the lights sequence up the pump on the system should also, maybe you will hear it revving up., It could be a stuck or failed pump. So having a spare pump serves as a troubleshoot and replacement should the system pump be bad.

With a 2 hour drive I would have all the options along with you. Pump, sensors, ohm meter, new wire connectors. It's not a super expensive control compared to multiple 2 hour trips, to have a spare with you. If you don't break the seal on the box, your supplier would probably take it back.

Often times it is best to be in front of the control when you have a support person on the phone. Facetime is a great troubleshooting tool that we use, it let me see the screen as you make adjustments.

I think you mentioned that you hit the test button and the light bar did ramp up. But did the pump?

With no errors on the screen sensors should all be connected, but certainly one could be out of spec and not sending proper info. The screen or the resistance test confirms sensor accuracy. Every sensor connected can be read in the view screen.

Mix supply sensor, doing that with the Boiler supply sensor is contingent on the BOIL MIN adjustment and could be confusing. Sure add that to your testing tool box.

In my mind, using the substitute resistance for a sensor is a complete test of the Tekmar 356 and its settings. and you can easily simulate other temperature conditions. As previously mentioned the sensors can be verified with an ohmmeter (multi-meter) if the sensor's temperature is known.

I build a number of simulators for our solar controllers. The engineer that came up with the design had me put a little rebel resistor in series with the POT. As I recall is serves several functions, allowing more range and prevented a short when cranked all the way down? Is that the intent?

These controls uses 1000 ohm sensors.

These were 20 turn POTS.

@hot_rod adding fixed value resistors to a potentiometer circuit would most likely limit the simulation range and/or offset the potentiometer's simulated range to a more desired temperature range.

For this application, a 10K at 77 degrees F (25 degrees C) thermistor I like a 10-turn 100K potentiometer. It provides a temperature range of -5 degrees to over 383 degrees simulation. Obviously the resistance range that simulates 212 to 383 is pretty useless, but it is less than 1/10 of one turn (1000 Ohms) of a 10-turn 100K potentiometer (212 F = 678 Ohms, 383 F = 72 Ohms). However, if desired, you could go above the 383 degrees of simulation resistance with less than 72 Ohm and test the Tekmar's short circuit detection functionality.

Also with 10-turn 100K potentiometer you can count the turns 10,000 ohms per turn (easier math for me), in this case so you can loosely keep track of the resistance without using the ohmmeter with simple testing.

I would wire the potentiometer so the resistance increases when turned Clockwise. If you want the potentiometer to increase the simulated temperature by turning the potentiometer Clockwise you could do that too, personal preference.

It's all about knowing how you want your simulator to work, its capabilities and knowing the component values to get that accomplished. Simulators can be as simple as a single potentiometer and some clip leads or in the case of the Tekmar 356 using 3 potentiometers since there are three sensors. Features like WWSD can be verified in the winter, outdoor reset can be verified in the summer, Mix and boiler temperature all at the same time without moving things around.

If it was me and I did a lot of Tekmar work (and the need was there) I'd put three potentiometers in a box with ohmmeter test points and an isolation switch for quick setup and changes. I'd use good test prod wire so I would not be repairing it all the time. I like tools that make my life easier.