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2 Questions (Outdoor Reset, Short Cycle)

jt3 Member Posts: 31
Boiler Triangle Tube Solo 110

Question 1

Re: Outdoor Reset Sensor Accuracy

Does anyone compare the reading from the outdoor sensor with the actual outdoor temperature and make sure they are close? (within a degree or two)  Checked mine a month or so ago when we started needing heat and the house seemed kind of cool.  Found the outdoor sensor reading a consistent 6 to 8 degrees F higher than the actual temperature.  (checked the temperature at the sensor location with a digital and outdoor dial thermometer which read within a degree of each other while the outdoor sensor was reading 6 to 8 degrees higher.  Have done this several times over the last month, always with the same result.)  I am assuming that this will make the “Target” temperature for the boiler lower than it should be since the sensor thinks the outdoor temperature is warmer than it actually is.

Short of changing the sensor, would raising the Reset Curve for Coldest and Warmest Day by 6 to 8 degrees compensate for the difference or would this cause some other problem that I’m not seeing?

 Question 2

Re: Short Cycling

Changed my primary zone pump from a Taco 007 to a 008 dT set to 20 degrees.  When I did, I checked with TT Tech support to see if it the internal circulator setting should be changed.  It is currently on the highest setting and he suggested leaving it there to prevent flashing in the heat exchanger.  Except on a DHW call which maintains a 40 gal indirect tank, the system short cycles.  Will be adding some high output baseboard to the system next year which should help but until then was wondering about the options.  The CH Post Pump Time is currently set at the default of 1 minute.  The boiler is firing for about a minute, getting the return temperature a couple of degrees above the target temperature and shutting down.  The circulator continues to run and about 1 minute later the burner begins the firing sequence again.  Since the burner won’t fire during the Post Pump, was thinking of extending the Post Pump time to 3 to 5 minutes to see if I can get a larger drop in the return

temperature and a longer firing time on the burner when it does fire.  And again, could this cause any problem that I’m not seeing?

Any better (no cost) options than what I’m thinking.



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  • SWEI
    SWEI Member Posts: 7,356
    next steps

    Measure the resistance of the outdoor sensor with a DVM after disconnecting it from the terminals on the MCBA.  Values at different temperatures are listed on page 31 of the Troubleshooting Guide.  If it's off, TT should send you a replacement.

    Look at INFO parameters 1 & 2 while the boiler is firing.  Turn the circulator down until you get a 25-30 degree difference between the two when the boiler is running at high fire.

    Is there some reason the boiler is piped with primary/secondary piping?  What kind of radiation and head do you have in the distribution loop?

    I assume there is a third pump dedicated to the indirect.  What kind of pump, and what kind of piping ties it together?
  • Paul48
    Paul48 Member Posts: 4,469

    try lowering the delta-t of the circulator. I would think that expecting to maintain a 20* delta-t at anything other than design temp is unrealistic. With the variation you know exists with your outdoor sensor, and the fact you mention adding emitters(which suggests you know the boiler is over-sized), your boiler is losing the battle.
  • jt3
    jt3 Member Posts: 31
    SWEI & Paul


    Is the MCBA the old TT Controller?  I should have mentioned that mine is the

    Trimax.  Looked in the TT Literature section and didn’t see anything that looked like a troubleshooting guide for the Trimax.  I have the Installation  / Maintenance Manual and the Control Application Supplement but don’t see anything for troubleshooting the outdoor sensor.  (Will take some readings tomorrow to see what I get.)

    I’m guessing that the “Info parameters” you are referring to are either in the troubleshooting manual which I don’t have or they are deeper into the control system than I have access to. (My documentation refers to everything by a function name such as CH1 & CH2 Minimum & Maximum Setpoints etc.)

    I didn’t do the plumbing but my understanding is that this boiler is supposed to be piped primary & secondary.  The boiler is piped as shown in Fig 9 on pg 21 of the installation manual.

    Heat is provided by 2 zones of the basic Slant Fin Baseboard.  1st floor zone is about 150’ total length of  ¾” copper.  That length includes about 45’ of baseboard.  2nd floor zone is about 180’ total length but only has about 25’ of baseboard.  System worked well with the old boiler and 180 degree water but doesn’t put out much heat when your running 130 degree water through it.  That’s why I’m thinking of replacing some of the 1st floor standard baseboard with high output.  Probably replace 14’ plus add another 12’ and if I’m reading the charts correctly, it should kick the output up by about 50% over what I have now.  Besides giving me better heat when the system is putting out 130 degree water, it should also allow me to turn down my max temperature so I don’t need to run 180 degrees except in extremely cold weather.  (Design temp for my area is 8 degrees.  I should be able to set my max temp lower

    than 180 or leave it at 180 but set my outside temp to zero or below. 

    Indirect is pumped by a Taco 007, ¾” copper to an AMTROL 40 gallon tank about 8’ from the boiler.  AMTROL is fed from an 80 gallon solar hot water tank so the  AMTROL acts as the backup to the solar tank.  Some days the AMTROL gets 130 – 140 degree water from the solar tank, other days it is basically ground water temperature.  Just depends on how much sun and how long it shines.


    If I understand my problem correctly, I’m not pulling the BTU’s out of the water fast enough, i.e. the water returning to the boiler needs to be cooler so that it doesn’t short cycle.  Because there is an internal boiler pump that is probably pumping at somewhere around 5 gpm in the primary loop and my heating zone is probably moving 1.5 to 2 gpm, the majority of the water being heated is circulating in the primary loop and not cooling at all.  The boiler will not fire during the post pump

    cycle, even with a call for heat.  What I’m thinking is that by extending the post pump time, once the boiler stops firing it will give the zone pump time to circulate all of the water in the system and bring it all down a few more degrees.  This not only keeps the boiler from cycling back on after only a minute or so, it lets it run a little longer when it does fire because all of the water in the system should be cooler.  By dropping the dT to 10 degrees the water will circulate faster but it probably wouldn’t cool down as much. (just a guess, don’t know for sure.)  What I really need is 4” thick concrete floors with radiant heat but that ain’t happening in a 100 year old New England Colonial.  : )


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  • Zman
    Zman Member Posts: 7,441

    This is much easier with the trimax. I just finished a system very similar to yours. The boiler circ when piped primary/secondary should be on 1 . That is from the West coast tt trainer.  On the trimax you can view the boiler delta t on either the main screen or in the info menu. I think a delta t on the system side of 10 to 20 is good.

    I think the issue you are experiencing is that the lower water temps are reducing the output of the baseboards and causing short cycling. The low cost fix is to raise the boiler temp curve. This will cost you some efficiency. The other option, as you suggested, is to install low temp baseboards.You can look for the sensor test procedure in the old manual, it hasn't changed.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • SWEI
    SWEI Member Posts: 7,356
    sensor test

    Thanks, Carl.

    Went looking for the 12k thermistor table last night and don't see it anywhere in the TriMax books.  The Service Technician's Troubleshooting Guide seems to be temporarily AWOL as well  I'm emailing Page 31 to him -- trying to get the OAT sensor to 77F this time of year can be a challenge.
  • jt3
    jt3 Member Posts: 31
    Zman & SWEI

    Thanks Guys,

    Bumped the reset curve Coldest Day setting from 8 to 16 degrees which kicked the target temperature from 142 to 148.  Dropped the boiler circulator down to the lowest setting which got my dT readings on the boiler to between 8 and 10 degrees with both heating zones running.  (007 & 008 dT set at 20)  With both zones running the total cycle time was about 3:45.  (Fan Start to Fan Start)  Haven’t seen it yet with just the 008 running.  Going to start adding a minute at a time to the post pump time to see if I can stretch the cycling out without affecting the heat.  If I can put in the high

    output baseboard and change the 007 pump next year it should make a difference.  Also need to figure a way to scavenge some heat off the main zone return line for the cellar.   Without the old WM down there it is already starting to get chilly.  That should also help with the cycle times as it will pull more heat of the return.


    Got your note and responded.  Will let you guys know what I get for readings when I get the new meter.

    Thanks again,


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  • SWEI
    SWEI Member Posts: 7,356
    primary circulator

    If you're seeing only 8-10F on high fire, you're still moving 3x the water you need to (but is that at high fire, under a heavy load?)

    Again, I'm curious why you have primary/secondary piping at all.  One of the primary benefits of the TT fire-tube HX is the elimination of the need for primary/secondary piping in the vast majority of applications.  The factory-provided circulator is fine for the indirect, but a smart circ works far better in most installs.
  • jt3
    jt3 Member Posts: 31

    The 8 to 10 degree differential is with both circulators running.  I know the 007 is moving too much water but don’t have the cash right now to change that one out.  (will change if I hit Powerball tonight : )  ) The boiler fires on medium or high fire (solid black flame icon) and then throttles back to a lower burn. (just a black outline for the flame)

    The installer put in Primary / Secondary because that is what the installation manual recommended.  It also recommended a separate pump for the DHW so there is a 007 pump for that loop too.  Boiler pump just circulates in the primary loop. You bring up an interesting point though that I had wondered about which is "Should the indirect also be on a dT pump?"

    Did get a note today that the multimeter is now scheduled for delivery today so might have it by the time I get home this evening.


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  • SWEI
    SWEI Member Posts: 7,356
    boiler piping

    8-10F will work, you can optimize later once you measure at full load.

    There's a statement at the beginning of the boiler piping section of the I&M manual titled "best practice" that smells like lawyer-speak.  It's followed a mountain of piping diagrams, only two of which show direct pumping configurations (page 22.)  Installers and designers who have experience with TT or have been through the factory training will direct-pump in most cases -- it simplifies the system and reduces both first cost and ongoing (operating) expenses.  Either way, it will work.

    Indirect on a ∆T pump would be great, but they can get pricey.  The Taco HEC-2 (BumbleBee) should be priced very similarly to the equivalent 008VDT circulator (but it only comes in that one size right now.)  Keep your eye on it - they're supposed to start shipping quantities in January.  Putting the HEC-2 where it will run the maximum amount of hours and moving your current VDT pump to a less-used position (like the indirect) would be ideal.

    I'm not really a fan of boilers with built-in circulators since we end up replacing them in the majority of installs.  If the boiler manufacturers provided circulators modulated by the boiler controls, I'd completely reverse that position.

    I've attached a (hopefully readable) chart with the 12k thermistor values.
  • jt3
    jt3 Member Posts: 31
    edited December 2012


    Made some changes since the last post.  Bit the bullet and replaced 23’ of SlantFin

    15 with Multipak 80 plus added an additional 4’ of the Multipak 80 plus 2’ of the SlantFin 15, all on the 1st floor zone. 

    Had eliminated the setback on the thermostat at night but the house still seemed to drop a couple of degrees overnight and took quite a while to get back up to temperature in the morning, especially if it was a cloudy day. (no solar gain).  With the new baseboard I don’t think the temperature is dropping at night.  The 4’ Multipak and 2’ “15” went into areas that were unheated before and depended on the heat from the rest of the zone to cover them.  (6’ x 7’ entry way with stairs to the 2nd floor and a small 8’ x 8’ bathroom) Those 2 pieces probably made a big difference in reducing the temperature drop at night.

    Haven’t had a chance to check the cycle times but will do that in the next couple of days. 

    As far as the outdoor sensor goes, I’ve checked it on 2 different occasions now and got the following:

    Digital Reading           Ohm Reading              Solo Reading

         33.6                             34.4                             42

         46.4                             23.6                             54

    If I am reading the chart correctly the Ohm readings are lining up close to the actual digital thermometer readings but the Solo is indicating a temperature about 8 degrees higher.  If that is the case, changing the sensor won’t make any difference.  Anyone know if there is a calibration setting that the techs can do to bring the Solo readings more in line with actual temperatures?

    Everyone take care, stay safe and you and your families have a very Merry Christmas and a Happy, Healthy and Prosperous New Year.

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  • SWEI
    SWEI Member Posts: 7,356
    outdoor sensor

    Am I correct in assuming that "Digital Reading" is a digital thermometer mounted near the TT sensor?

    Are the "Ohm Reading" numbers in thousands of Ohms, or have they been translated?
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Common Sense

    The boiler is oversized and the fix was a buffer

    tank not adding hi output. Your still not pulling btu/hr

    out if the boiler.

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  • jt3
    jt3 Member Posts: 31

    That’s correct.  I have an indoor/outdoor thermometer with a remote sensor.  I balanced the sensor on top of the TT Sensor cover and left it there for an hour or so before I took the readings.  I also used a large outdoor dial type thermometer

    which read within a degree of the digital thermometer reading as a double check. 

    The multi-meter used is an Innova 3320 Auto-Ranging unit.  Nothing fancy but you switch it to the Ohms scale, apply the probes to the wires, and the system determines the proper scale to use.  The display will show a “k” or “M” above the reading if the unit is using one of the higher ranges.  While I didn’t remember seeing

    the k or M, I also wasn’t specifically looking for it since I expected the reading to be in the range that I saw on the scale.  Because of that I just took another reading this

    morning and they are on the “k” scale (1,000?).  This mornings readings were Digital Thermometer 47.1, Ohms 23.2k, TT Outside Temp Display 54 degrees.  Again,

    the Ohms reading would appear to me to be close to what the digital thermometer

    is showing, not what the boiler display is indicating.  (I’m sure I could figure it out exactly but that math class was 50 years ago and I’m kind of rusty on the concept. (Grin))

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  • jt3
    jt3 Member Posts: 31

    I'm finally coming to that same conclusion.  However, changing the baseboard did make a difference in the comfort level in the house.  Will see how things go this winter and probably add the buffer tank next year.  Was going to redo the primary loop and where the secondary loop connects to it but, if I understand the buffer tank concept correctly, the spacing between your supply and return becomes a mute issue since everything runs through the buffer tank. 

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  • SWEI
    SWEI Member Posts: 7,356

    The required math is not exactly simple http://en.wikipedia.org/wiki/Thermistor but the answer is 49.3F for 23.2 kΩ.  I'd call TT and ask why the boiler OAT is off.
  • jt3
    jt3 Member Posts: 31

    Thanks SWEI,

    That formula is a good example of why they publish tables / charts.  I'll check with TT tomorrow or Tuesday and let you know what I find out.

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  • jt3
    jt3 Member Posts: 31

    Spoke with TT today and there is no way to adjust the display reading to match the OAT sensor.  The work around would be to boost the "Minimum Temperature" setting by 6* which is what I had already done. 

    Also asked if there was a way to adjust the "Differential" on the heating zones (CH1, CH2) like there is on the DHW zone.  Currently the boiler kicks back on when the output temperature drops 2 degrees below the target temperature.  Figured if I could set a 10* to 15* differential it would help with the short cycle times.  No Such Luck.  That one is not adjustable.  Will watch and see how it goes if the weather ever gets colder.  (almost 60* here today)  Never thought I'd be wishing for colder weather to see how the boiler works.  : )

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  • gennady
    gennady Member Posts: 839
    boiler sizing

    do heat loss calculations

    cut boiler output lower to match heat loss ( you will loose you turndown ratio thou)

    remove zoning, meaning manually open zone valves or set thermostats for 99F

    set 008dt to 35 dT

    you happiness will come to your boiler.
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