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Is my boiler operating correctly?

pwr_hngry Member Posts: 2
edited November 2019 in Radiant Heating
I have a Bosch Greenstar 151 Combi boiler that was installed last summer. Now that winter is upon us, I want to make sure it is doing what it should. It is fairly efficient at heating my hot water in my house and it is holding my temperature stable at 71 degrees. I have read a lot about short cycling and other issues and I want to make sure that my boiler is working alright. I am pretty sure that I do not have the outdoor temperature module.

House is about 2500 sq ft. Single level.
Heating is 7 loops but on a single zone.
Heat is radiant baseboard

The heat knob is currently set to 5 but, here in Wisconsin, we cannot consider it to be cold yet since the temperature is not getting much below 20. We will see -30 a few times before winter ends. I am wondering if I should crank it up to Max for my radiant baseboards? I read somewhere that they are most efficient when the water temp is around 180?

When I watch the boiler in these "warmer" temperatures, my zone pump stays running but the boiler temp will cycle up to 135 and the burner will shut down and then the water temp will cool down to 105 before starting another burn. The whole process takes about 5 minutes to get up to temp and about 10 -15 to cool back off. If I push it up to 72 or 73 the boiler goes into high burn and runs all the way up to about 153. Like I said, it is holding my temperature steady. Everything seems to be working correctly but I thought I would ask to see if I might be missing something. Thank you for your time and for sharing your knowledge.



  • Jamie Hall
    Jamie Hall Member Posts: 18,915
    Doesn't sound too far off. The reason the boiler cycles is that you don't need all the heat that it is capable of -- at the moment (come January, you just might!).
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,184
    There are temperature sensors on the supply and return inside the boiler. The brains of the boiler are calculating the difference between the sensors and determining what you need. as you need more the water temperature will get hotter.
    Outdoor reset only happens if the outdoor sensor is connected. Is the an outdoor sensor? Was it wired in?
    Attached is what I got from Bosch tech support in the event that you don't get enough heat, this will make the boiler more like a conventional boiler, less savings on fuel cost.

    I needed it for a customer that "just wanted the house to be the way it was with the old heater!"

    She was 87 years old and set the thermostat to 76° F but the system kept the house at 69° all the time.
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • pwr_hngry
    pwr_hngry Member Posts: 2
    I really appreciate the input guys. I made the switch last summer from an outdoor wood boiler to the Bosch. My outdoor wood boiler was roughly 2000 pounds and I burned through 17 cords of wood in the winter of 2018 -2019. Going to this much smaller propane boiler (yeah yeah, I know, its not the size that counts!) :) makes me a bit nervous. My back definitely feels better though!