Trane TZEMT400bb32 Shuts Off Before Target Reached and Short Cycles Back On

I replaced our battery-powered t-stat with a Trane TZEMT400bb32 about a year ago. I had to install an AC adapter to power this unit. We have a very basic set up with a Weil-McClain furnace and oil heat with radiators (hot water). There is no heat pump or AC. There is only the temperature sensor in the T-Stat itself.

Here is the issue. It seems to be run-time-related or something. The schedule is set to 61 over night. At 7am it turns on to heat the house to 68. What is happening is that it gets to 66 after an hour or so then shuts off before reaching the target.

Then after a short period of wait time, it comes back on for a short period and shuts off prematurely again.

We have played with the Heating Delta Stage 1 On and Off settings to no avail. I have also tinkered with the T-Sense Match setting thinking that the temp sensor isn't being queried ofent enough or something.

I am about to reinstall the old unit to see if that helps. Does anyone have any advice? Does the furnace have some sort of overheat protection or something? We have it cleaned out yearly. It does NOT have a filter.

Thanks in advance. This has been driving us nuts and hopefully doesn't break our furnace.

Edit: Its a boiler not a furnace.

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JLMCDANIEL avatar
1 month ago #2
JLMCDANIEL
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Is the max temp set in the installers section?
The Delta Stage 1 off should be 0 unless it heats about set temp.

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echardcore avatar
1 month ago #3
echardcore
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Thank you JL. The max temp is set to 75 and I had the Delta Off at 0 previously. But we've monkeyed with it so much I've set that back. Let's see. Any other possibilities?

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JLMCDANIEL avatar
1 month ago #4
JLMCDANIEL
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Make sure that the multistage is set to no.
There is also an adjustment to the reading temperature so you can adjust it if off. Check you room temperature and make sure the displayed temperature is correct.

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echardcore avatar
1 month ago #5
echardcore
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Thanks again JL! I think its fixed! I have the multi stage turned off and I did calibrate the sensor with another thermometer. No more short cycling! I think it was that Delta Off setting. After changing so many different things you lose track. I read the manual a dozen times and also read the manuals for similar models. Glad we don't need a service call!
Cheers

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JLMCDANIEL avatar
1 month ago #6
JLMCDANIEL
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Glad it is working for you. Good Luck.

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echardcore avatar
2 weeks ago #7
echardcore
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Hi again. The problem came back. I tried playing with some more settings like T Sense Match (sensitivity) and others with no luck. I swapped in the old T-stat and it seems like the issue isn't happening but there is a faulty button preventing me from editing the schedule. I guess I'm going to buy another unit but here's my issue now.

I have a strange situation where I have two wires coming out of the electrical box on the boiler that magically turn into 3 at the T-stat. I can see the splice. Red and white at the boiler and a green appears at the t-stat. What the heck? Is this necessary? I want to get a new wire. Could this be part of the issue?

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JLMCDANIEL avatar
2 weeks ago #8
JLMCDANIEL
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"G" is for running the fan on a forced air furnace when switching from fan auto to fan on. Would not be used on a boiler. It should not cause a problem because it is an output from the thermostat.

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2 weeks ago #9
echardcore
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Thanks much. Didn't think that was needed. Wonder why they (previous owners/techs) did that. I'm going to install a new wire when I install the new unit. I picked this up based on good reviews.

Lux Products TX9600TS Universal 7-Day Programmable Touch Screen Thermostat https://www.amazon.com/gp/product/B0044UYVFW/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

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JLMCDANIEL avatar
2 weeks ago #10
JLMCDANIEL
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Be sure to read and understand the setup procedure.

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echardcore avatar
2 weeks ago #11
echardcore
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So it happened again with the original thermostat. Is there any possibility that that extra wire might be sending a signal to turn the boiler on? The green has to be spliced into either the red or white. I'll find out when I take the wore down this weekend. The t-stat might be sending a "turn fan on" signal which is activating the boiler. Not sure if this is possible or not.

Otherwise I'm going to need someone to come out I think.

Edit. My SO says I'm explaining it wrong.

Target temp isn't reached. Boiler shuts off before target is reached then comes on again shortly after.

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JLMCDANIEL avatar
2 weeks ago #12
JLMCDANIEL
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If the green is spliced into the white wire it would turn on the boiler when the fan switch on the thermostat is turn on instead of auto. Just disconnect the green wire at the thermostat.


Check the anticipater in the thermostat if it is an old type http://homerepair.about.com/od/heatingcoolingrepair/ss/adj_anticipator.htm

If it is a programmable unit check the settings.

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echardcore avatar
2 weeks ago #13
echardcore
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Okay it is programmable.

The guy at home depot mentioned an exhaust fan. It's that anything I need to worry about?

Also. This problem only seems to happen in the AM when the house is at its coldest and it runs for an hour or so. It seems that with the modern Wi-Fi T-stat, it won't reach target, stops, and comes on again shortly after. The older T-stat that's installed now, it overshoots, goes off, then comes back on.

Really hard to describe. Very frustrating and worried about the short cycles damaging the system.

Can it be overheating?

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