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Buderus G115 Strangeness

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JWH
JWH Member Posts: 13
in Oil Heating

I got a call from a customer stating that their boiler isn't keeping up with the load during a current cold snap. It has been -25 to -30 here for a week. The boiler is a roughly 20 years old Buderus G115 with Riello F5 burner.. The house is all radiant slab heat. I did the annual service on this boiler two months ago. Nothing wrong on visual inspection. Unit has been running constantly and not breaking 130 degrees. I check the unit with a combustion analyzer and all is as I left it. Stack temp 340 degrees F, CO2 11.43, O2 5.6, trace of smoke. Its had a .60x60B and 175 PSI pump pressure. I upfired the unit to .65x60W and 190PSI then adjusted to 11.5 CO2. The unit gained a few degrees of water temp. Everything in the house is calling for heat, but this unit has heated this house at -50 in the past. Am I missing something or is this a load problem rather than a boiler problem?

Comments

  • kcopp
    kcopp Member Posts: 4,614

    What type of tubing is in floor?

    Are you sure its O2 barrier? Is it Onex epdm tubing?

    Are you sure the circulator(s) is running? Any chance to shoot the floor out for temp? Flir camera?

    HydronicMikeJWH
  • JWH
    JWH Member Posts: 13
    edited December 13

    The slab tubing is barrier PEX. I looked around the house with an IR camera, I can see all the tubing is warm in the slab. I didn't see any glaring cold spots. The system is all pumps and they all work. Lack of flow would cause the house or part of the house to be cold, but it would not also make the boiler run 24/7. If there was scale buildup in the jacket or soot in the flue passages, the stack temps would be high.

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 19,455

    Strange.

    I wonder if something is interrupting the burner operation? But you said it is running constantly. The heat must be going somewhere.

    JWHGrallert
  • HVACNUT
    HVACNUT Member Posts: 7,198

    Max SWT is only getting to 130°, so what's the return temperature? Whats the mix temperature? Amp draw on the circulator(s)? Are there flow meters on the manifold(s)?

    Too much draft? Should be -.02 at the breach. Riello wants 326° net stack temperature with a .65 nozzle on the G115-4.

  • JWH
    JWH Member Posts: 13

    I spent most of yesterday there. The burner never shut off. I had the combustion analyzer connected monitoring. Draft was -.02 at the breach. Yes, when I upfired to the .65 nozzle, stack temp rose to about 375 degrees. I installed the second stage baffles and the stack temp came down to about 330 degrees. I didn't do an amp draw on the circ pumps and there are no flow meters. Supply temp stayed around 130 and return temp at the 4way mixing valve was around 80 degrees. There are a few HT zones that I don't know exact return temps on, but the supply and returns felt the same. I shut off zones and the boiler comes up to temp and turns off. Its so cold at the moment that all the zones are cold and makes diagnosing which zone is the problem difficult.

  • psb75
    psb75 Member Posts: 1,099

    Well, don't they say that a properly designed and built system should theoretically run constantly in "design conditions" i.e. when temps are the in the targeted "design degree" range? A report of more of the HT and slab "delta T's" would be helpful to you and this forum. Even reports of room temps would be helpful data.

    Ironman
  • kcopp
    kcopp Member Posts: 4,614

    -25 is Cold… Very cold. Is that normal for there? Has that been typical for the last 20 years?

    Was that what the system was designed for?

    Sounds like everything is working fine.

    Has the envelope changed in the last year?

    Ironmanhot_rod
  • HVACNUT
    HVACNUT Member Posts: 7,198
    https://forum.heatinghelp.com/discussion/comment/1877013#Comment_1877013

    Its -25° to -30°. He says it can maintain temperature at -50°.

    @JWH , how is the pressure? Is the feed valve open? Is it possible there's a leak and it keeps feeding cold water?

  • psb75
    psb75 Member Posts: 1,099

    Oh yeah. I missed that… MINUS 50! Kind of crazy. Must be MN or AK. Or Canada.

  • Ironman
    Ironman Member Posts: 7,849
    edited December 13

    A 40* delta T on the slab is way too high. It sounds like too little flow or else the slab is imposing more load than the tubing can emit.

    Do you know for certain that it was able to keep up at -50*? Was that just for one night or for an extended period of time like you’re now experiencing?

    What’s the design temperature for your locale?

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Big Ed_4
    Big Ed_4 Member Posts: 3,348
    edited December 13

    Is there a set back on the system ? Does the thermostat use a floor sensor ? Heat loss .. AC system in the house ,with open defusers and return grill ?

    There was an error rendering this rich post.

  • hot_rod
    hot_rod Member Posts: 26,527

    The heat load calc and system design was done at a -50°F design day?

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • psb75
    psb75 Member Posts: 1,099

    I think the OP froze up! Too late.

    JWH
  • Tom_133
    Tom_133 Member Posts: 956

    I had a similar situation, and it turned out to be the buderus control on top of the boiler, the clock setting was off PM to AM so the night time set back was happening all day. After a good few hours of working on that I found the issue, and taught the customer that a 10 degree setback on a radiant system was not going to work well.

    Its most likely not the problem here, but a funny antidote.

    Tom
    Montpelier Vt
    JWH
  • JWH
    JWH Member Posts: 13

    Sorry for the delay. Design temp is normally -38F. The rooms were set for 68, but only getting to 63. System is 30% glycol and has a tank that has an on demand pump to feed the system, but I keep the feed valve off. I want to know when there is a leak. -40 happens occasionally most winters. -50 is rare, but has happened multiple times in past 20 years.

  • JWH
    JWH Member Posts: 13

    I have been wondering about the control. It is the old Logimatic. They aren't user friendly... The mechanical hour meter in the control stopped working at some point in the past so I can't tell hours. If it was shutting down, it would be less than 63 in the house.

  • JWH
    JWH Member Posts: 13

    The house has smart thermostats and they had been turned down to 60 for more than a week. Then they were turned back up to 68 anticipating people coming back, but it never got above 63 after 4 days of running. No setback on the boiler. Outdoor reset, but that wasn't causing the issue.

  • Big Ed_4
    Big Ed_4 Member Posts: 3,348

    Try not using the set back durning the cold days …Slabs can take 6 hours heat and 6 hours to cool. …

    There was an error rendering this rich post.

    JWH
  • JWH
    JWH Member Posts: 13

    I recomend not doing setbacks on radiant unless you'll be gone at least 2 weeks. The house was empty for a month.

    kcopp
  • JWH
    JWH Member Posts: 13

    It warmed to -10 outside and all zones satisfied.

  • Ironman
    Ironman Member Posts: 7,849

    I think that you have the answer: the outdoor temp dropped to -28* with the system in setback, then when it was set to come back up, it couldn’t because the mass of the slab and structure was too much for the system to overcome.

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    HVACNUTGrallertJWH
  • Big Ed_4
    Big Ed_4 Member Posts: 3,348

    Check the program in the Nest , it could have taken control :)

    There was an error rendering this rich post.

  • Tom_133
    Tom_133 Member Posts: 956

    The good news is you dont have too much boiler, or not enough. If no setback and the outside reset is setup well, than its a good match!

    Tom
    Montpelier Vt
    JWH
  • Big Ed_4
    Big Ed_4 Member Posts: 3,348

    Also ..There is no boost on Buderus constant circulation controls . Reset works ok in the milder weather but shut it down in the colder days..

    There was an error rendering this rich post.

    JWH
  • GW
    GW Member Posts: 5,135
    edited December 14

    we talking F or C ?

    May need to increase capacity or reduce heat loss

    Slab—- insulated? Running water or high water table?

    ahh yes just read some more- setting back on a slab isn’t a good move. Adding in extreme cold- downright user error

    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
    JWHIronman
  • JWH
    JWH Member Posts: 13

    All temps are Fahrenheit. Yes, the garage is the only slab on grade, and is insulated from the ground. The rest of the house is over an insulated crawlspace that I didn't have access to. Radiant tubing is in 2 inches of concrete overpour. Running water and high water table were both things I considered. It may have been just bad timing. They have gotten away with setting back the temperature while out of town and turning it up shortly before coming home in the past. This time it coincided with a cold spell and the boiler that is big enough to maintain has no reserve to overcome the excess load. The house warmed up when outside temps came up. It's forecasted to be in the -30s in a few days, so we'll see…

  • Ironman
    Ironman Member Posts: 7,849

    The G115 can be up fired by 10%, but not down fired. So, you may be able to increase the firing rate a little more.

    I don’t have the spec sheet readily in front of me, but it gives the parameters if you can locate it in their literature.

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    GrallertJWH
  • GW
    GW Member Posts: 5,135

    if the temperatures are extreme, as you indicate, no normal heating system is designed to handle that, at least in my part of the woods, Massachusetts

    Negative 25 to 30 is silly cold

    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • JWH
    JWH Member Posts: 13
    https://forum.heatinghelp.com/discussion/comment/1877392#Comment_1877392

    Yes. Changing from the .60 to the .65 nozzle at 190 psi was the upfire spec. It changed from 112k btu to 124k btu.

    Heating systems here are designed for an average coldest day of -38F.

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