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HELP, Weil-Mclain Ultra 155 is not modulating

Tom Elam
Tom Elam Member Posts: 57
I don't have a Parameter 11 on my boiler. I think my boiler is a Series I.


  • Tom Elam
    Tom Elam Member Posts: 57
    HELP!, Weil-Mclain Ultra 155 is not modulating

    Our boiler is not modulating the flame. We purchased and had it installed in the summer of 2004 so I believe it is an Ultra Series I. We use the boiler only for heating the house.

    Today the outside air temp was 52° in Kingsville Maryland.
    I noticed it took about 2 minutes for the boiler water temp to get up to 162° so I know something isn't right.

    The Control Mode parameters are set as follows;

    1. DHW setting 138

    2. DHW setup 01

    3. Space heating setup 01

    4. Outlet Water Temperature 156

    The Information Mode readings were;

    1. Measured outlet water temperature 162

    2. Return Water Temperature 154

    3. This fuction not used -22

    4. Outside temperature 52

    5. Flue temperature 146

    6. Target outlet water temperature 156

    7. Outlet water temperature change 00

    8. Return water temperature change 00

    9. This fuction not used 00

    According to the chart in Figure 5 of the boiler book the Target outlet temperature should have been somewhere around 110°. This boiler is firing hard and running up to the Target outlet temp (Parameter Mode 4)as if the outside air temp was 32°. The Outside temperature sensor is working because it indicates 52°(Information Mode 4).

    Does anyone have an idea of what might be wrong with the boiler? There are 2 small fuses on the control module, a 4 amp slo blow and a 5 amp fast blow. I haven't checked them but I don't think the boiler would even run without either one of them.

  • tim smith
    tim smith Member Posts: 2,752
    Mod temp to high

    Could be a defective outdoor sensor or water temp sensor. I don't know for sure whether when fails does it ramp up to high temp setting or would it just stay at min. setting. Tim
    I just went out and checked control supplement, if something else awry in system, and boiler running long cycles, the control adjusts temp up I think 5 or 10 degrees or so for every 10 minutes of uninterrupted heat cycle. Just a thought other than one of the 3 sensors.
  • Tony_23
    Tony_23 Member Posts: 1,033
    Incomplete info

    Need to know your "foot" setting for water temp. This would be the lowest water temp at the highest outdoor temp. It determines the base of your curve. All water temps will fall between the "foot" and the "top".

    If your design temp is 32 (doubt it), you can start there. Otherwise, you need your design temp programmed in, in place of the current 32.

    You should call the installer or servicer to do this, these settings are not accessible by the end user in general.
  • Tom Elam
    Tom Elam Member Posts: 57

    Thanks for the reply,

    The outside temp sensor showed 52° on the boiler and that matches the outside air temp. The differance between the water return temp and outlet temp is 8° so they are probaly working also.
  • Tom Elam
    Tom Elam Member Posts: 57

    I don't see what my "foot setting" is on the Information Mode so I don't know that set point. In the Boiler Manual Operating information it says the Parameter mode Left digit shows 3, Right digit should show 1 and "Do not change this setting as it might affect boiler performance".
  • Floyd_47
    Floyd_47 Member Posts: 2
    I think your wrong...

    judging from the info you got there the boiler is running at a low fire, otherwise your flue temps. would be at or higher than the return water temp. That boiler will run lower than return temps. at those output temps. when it is running at a very low modulation. Now that being said, I think the your reset curve is messed up and the temps. are higher than they need to be for the outside temperature that you have. This could be the result a a number of things... If the boost feature had kicked in the cycle before and raised the reset temps., the boiler will only back them down 1 degree per minute of off time and thus the target temp could be skewed...
    The only way you can really know what is going on is to have an experienced installer or serviceman hook a computer to the module through an interface and look into what the control module is doing.

  • Tom Elam
    Tom Elam Member Posts: 57

    Can you recomend a good tech in my area to check it out?

  • > Can you recomend a good tech in my area to check

    > it out?


    I installed an Ultra 105 3 years ago, and have changed some of my settings to squeeze more out of it for comfort and efficiency! Par #11 is temp boost, what is it set at? Factory setting is 10! Every 10 mins it will raise the temp 18 degs until the room temp has been met! I run mine at 0, so there is no temp boost! The system runs almost continuos and the condensate pump runs alot! Which is gooood! Better efficiency at lower return temp! Changing par# 11 to 0, & my outside temp 47-50 deg, my target temp is 94-112 but if I change par #11 to between 1 & 30mins it raises the target temp up to about 156 deg at the same outside temp of 47-50deg! My high limit is 160! Hope this info helps!


  • Is there a parameter listed for temp boost in your manual? If not contact your local tech or regional are rep. I checked WM site, no tech manual for series 1. Our company installed maybe 1 or 2 of the series 1, rest of our installs the past couple of years has been series 2, haven't had any problems with them!
  • Tom Elam
    Tom Elam Member Posts: 57


    I just woke up 11:30 am, raised the bedroom thermostat then ran down to the boiler. Outside temp is 58. The boiler water outlet temp slowly got up to 122° then the boiler stopped firing.

    I sat in the basement and did my morning devotionals and listened to the boiler cycle. When the burner stopped firing the boiler water outlet temp was 138.

    I ran upstairs to fire up the computer and started typing this message. I went to check on the status of the boiler and it was firing again. This time it stopped firing at 152 boiler water out temp.

    I completed a couple of chores and checked on the boiler and it is firing again. The boiler water outlet temp got up to 150 then the thermostet told the boiler to shutdown because it was satisfied.

    This whole deal took 50 minutes to complete. I lookd at the visible emission from the boiler stack and it appeared the boiler was not firing at the max rate.

    In conclusion: The boiler kept raising the water outlet temp every time it cycled. Is my concern justified or am I over reacting? Do you think this is something covered by my warrenty or will this be an out of pocket expence?

    I want the boiler to run as efficently as possible. The house is 1850 ft2 rancher with 2 zones of baseboard heat and a radiant zone in a bathroom floor.

  • Tom Elam
    Tom Elam Member Posts: 57

    Yes it does. Parameter 3 is my space heating setup. Quote from manual; "Left digit shows 3, Right digit should show 1, DO NOT change this setting as it might affect boiler performance"

    Do you think this may be the ticket? Should I put in a 0 and watch what happens?

  • If you can't locate or get any info from the service tech that installed it contact the following, regional WM rep. The person I deal with is Ed Sanders

    Phone: 856-866-7400
    17000 Commerce Parkway, Suite B
    Mt. Laurel, NJ 08054
    Fax: 856-866-8828
    Hours: 8:00 a.m. to 5:00 p.m.
    Monday through Friday

  • Tom Elam
    Tom Elam Member Posts: 57

    I put in a 0 on parameter 3 and it appears the boiler will not fire. I killed power to the heating system to attempt to reboot the controls. When I powered it back up parameter 3 was back at 1.
  • Tom Elam
    Tom Elam Member Posts: 57

    Great! Thanks for your help Mike. Tom
  • Floyd
    Floyd Member Posts: 429

    Stop, already... your getting yourself in a tither over nothing... the boiler is doing axactly what it is programmed to do out of the box. Now, if you want it to do something else you need to find someone who can make it do what you want.
    That boiler is programmed to boost the output temp. 18* every 10 minutes.. my guess is that the flame is cycling but the call for heat is still there and the circ. pump is running, so the boost is kicking the temps. up, just as it should...
    Try "find a contractor" on this site for someone in your area that may be able to help.

  • Tom Elam
    Tom Elam Member Posts: 57

    I you are corret, the boiler is doing what it's programmed to do. I could see it increase the water outlet temp every time it cycled. I just want to get the max efficency out of the boiler. I don't understand why there is even an outdoor reset if the boiler water outlet temp is just going to eventually climb to the target temp anyway.

    I got a few local heating specialists off of Weil's web site. Are there any specail credentials that I ask for when I look for someone to reprogram the boiler?

    Thanks for your help Floyd, Tom
  • Tony_23
    Tony_23 Member Posts: 1,033

    It's probably oversized for the load to start with. Now it's grossly oversized since it's 58 deg out. It's likely modulating as low as it can, 31,000 BTUH, and needs 10,000.

    Get someone who knows how to program it for no boost and correct outdoor design temp and you'll be good. Have them do a combustion analysis while they are there, it's important.
  • Tom Elam
    Tom Elam Member Posts: 57
    The saga continues...

    Ok I found a tech to program the boiler! He asked me to figure out what paramertrs I want him to enter. This is what I've gleaned from everyone so far;

    1. Disable boost. Set it up for no boost at all.

    2. Correct outdoor design temp. Last Febuary was the 5th coldest on record. The temperature got down to 10°. Do I set the outdoor design temp for 10° or do I give myself some leeway and set it at 5°?

    3. Perform combustion analysis after making the adjustments.

    Thanks again for sharing your wisdom with me,
    Tom Elam
  • Uni R_2
    Uni R_2 Member Posts: 589
    Outdoor Reset Curve

    Tom, you might want to play around with the attached spreadsheet so that you can get a visual idea of the curve. The object is to try and keep your water temps out of the red zone where your boiler will not be condensing but still be able to maintain heat in your home.

    As you can see, the default curve for the Ultra tends to be very steep because of the max outdoor temperature being set at 32. I think someone meant 0°F when it was being spec'd from Honeywell Europe but this was a Celcius based controller that's been fudged to do Fahrenheit (the reason for 2° increments) so 0°F may have been thought to mean 0°C, hence it is 32°F.

    You can plot the curve down further than design if you want. Last winter the temps here went below design a few times. At design the curve flattens and the boiler temperature doesn't get any higher. The minimum outdoor temp available is -4°F (but that can be extended to -14°F by using P_09 and setting it to 10, although then you have effectively shifted the curve 10° to the right, and the boiler temps would all happen when it is 10° colder outside than in the graph).

    You can populate data in any of the white boxes. It's nice for keeping track of the curve settings in case it takes a few tries to get it optimized.
  • Tony_23
    Tony_23 Member Posts: 1,033

    No lower than 10, if that's what you've seen. No "cushion" required, it's already there.

    That being said, if you find someone with an ASHRAE handbook it will tell you the design temp for your area.
  • Tom Elam
    Tom Elam Member Posts: 57

    Thanks Tony.
  • tim smith
    tim smith Member Posts: 2,752
    Regarding design temp

    I would not set outdoor design at lowest temp seen, set it at local design temp, maybe 15 or so, with water temp design at low design od temp set at what you need based on heat loss. Then set the max temp at the limit of the emmitter to prevent floor damage based on flooring. The program will run temp higher up to max temp if you drop below design outdoor temp.
This discussion has been closed.