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First House.... Oversized, Short Cycling System.

Sean_34 Member Posts: 1
Hello, this will be our first full winter in our (first) house. I replaced the 6” galvanized exhaust pipe from the boiler to the chimney (SS liner, brick chimney exits roof in middle of house/garage) last year as it was in very, very bad shape. I am aware that it hasn’t gotten very cold yet, but am concerned with the very short cycling of the boiler, remembering the rotted exhaust (condensation).


Viessmann Vitorond VR2-33 (2003) w/ Riello F5 and Vitotronic 100 KK5 controller 167*F high limit

Vitocell 100- 42gal indirect DHW HL-135*F diff-7*F

Taco SR506

Taco 007 circulators


1250sqft ranch, built in 1993, I calculated heat loss approx 27K BTU/HR@ 10*F

zone #1 Kitchen/Livingroom has 24’ of ¾”slantfin 15? - H/L for that area 14K (under radiated??)

zone #2 Bedrooms 37’ of ¾” slantfin 15? – H/L for that area is 13K

zone #3 ½ finished basement, heat is off down there until I can swap out ZURN potable PEX. (doh!)

zone #4 DHW 1” copper

Tstats zones 1&2: 68*F morning, 64*F during day, 70*F evening, 66*F night ; 2*F DIFF

Not being an expert on the subject Id say the boiler is oversized 300%?. I have been researching the Tekmar 260 as it seems to me when installed properly can extended periods of time between burn cycles/ increasing length of burn itself. Saving fuel is nice but my primary concern, after comfort, is equipment health and longevity. Since turning the heat on this season I am averaging 2min-on 10min-off cycles; that’s with zones 1&2 calling. Ive seen a couple 10min runs maybe when 1,2&4 call on cold start?

Boiler is wired cold start, I just connected the internal pump aquastat last night (wasn’t done previously) which now energizes the Zc terminal of the SR506 (allowing circulators to run) once boiler is heated to (90*F) desired temp.


Is it better to have the circulators come on for boiler cold start and heat the zones and boiler together or allow the boiler to get to a higher temp before turning the circulators on (thermal shock)?

Will the Tekmar 260 be effective at giving me longer, more effecient burn times.

Thanks in advance. –Sean.


  • icesailor
    icesailor Member Posts: 7,265
    Short Cycling:

    The colder it gets outside, the longer the burner will run. Wait until it gets really cold in January and see how long it runs.

    Sounds like it is fairly normal to me.
  • Jim Davis_3
    Jim Davis_3 Member Posts: 578

    The circulator pump should come on no later than when the burner comes on.  I used to recommend starting the pump just before the burners come on. 

    Short cycling does not eat flues.  Underfiing the equipment and combustion air problems do.  Controls can be set for longer on/off differentials to make the cycles longer. 

    Flue temperatures should be in excess of 400 degrees in oil, even in just two minutes.  If not there is something wrong.
This discussion has been closed.