To hot - Boiler Control and Thermostat CG8

AlwaysLearning2024

Hi everyone,

Trying to wrap my head around a “too-hot” condition in my 4-family apartment building.

Current Installation:

• WM CH8 series 11 (202,000 output)
• 2-Pipe reverse return hydronic system with fin-tubed recessed heat emitters.

The previous boiler control (which I do not remember, yet used small mechanical inserts that set times, and a knob to set the temp — very easy), was replaced with a Tekmar 256 with outdoor reset and pipe-probe.

I’ve had too-hot issues since the 256 was installed.

256 parameters are:

• Outdoor design is set at 10 degrees (Cincinnati, OH)
• Min 140 / max 180.
• Design 68 degrees

With these settings, I’m still nearly 78 degrees in room.
There is no external room temp sensor.

Curious if anyone has some tips or a better solution.

Thank you!

Jamie Hall

Constant circulation in the radiation and primary/secondary piping?

If so, start playing with the outdoor reset curve on the Tekmar. Your problem is running the ater through the radiation at too high a temperature.

AlwaysLearning2024

thank you @Jamie Hall . Yes, constant circulation. 1 zone.

I’ve been using the “automatic” boiler differential on the 256.

How would I start to adjust the outdoor reset curve on the 256v

EdTheHeaterMan

Here is the manual Tekmar 256. at the bottom of page 2 it reads "To make an adjustment to a setting in the control, press and hold simultaneously for 1 second, all 3 buttons. The display will then show the word ADJUST in the top right corner. Then select the desired item using the Item button. Finally, use the and / or button to make the adjustment."

EdTheHeaterMan

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.

AlwaysLearning2024

Thank you, @EdTheHeaterMan .

Yes, chose 4 as the heat emitter type.

I'll make the initial change of 180 to 172 and report back.

More soon!

EdTheHeaterMan

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.

109A_5

The demand input may be there for a reason.

AlwaysLearning2024

Thank you @EdTheHeaterMan

Seems there is a heat emitter type that corresponds with a number in the menu system on the 256. The choice of number "4" chooses the fin-tube variety.

Thank for @109A_5 — Seems that is connected properly and the boiler is firing.

Curious if using a 260 with a indoor room air sensor input could also help even out the heat? Or is this overkill?