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Oil Fired Boiler - Cold Start vs Warm Start

cdvo871 Member Posts: 6
I recently had my 2 year old boiler (Weil McLain WGO-3) serviced by my oil company and the technician that serviced it changed some of the settings - most notably he set the low limit temp to 140F. Previously that was set to OFF and my boiler was only firing when the thermostat called for heat. I do not have a tankless coil set up; I have a separate DHW.

The temperature here where I live has been pretty mild, 50s and 60s, and the boiler is running throughout the day without any call for heat - this seems wasteful, especially given oil prices these days. What is the benefit of maintaining this low temp all day if I don’t have a coil and using it for domestic hot water? The boiler has been running on “ cold start” since it was installed 2 years ago.


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,368
    edited November 2021
    Did you ask him why?
    What type of aquastat is on the boiler?
    Why type of emitters?
    Maybe when he cleaned it he discovered the boiler was condensing a lot, so he did what he did.
    If that’s the case, then the best thing to do would be to protect the boiler with a mixing valve and put it back to cold start. Even at cold start, the boiler will stay warm with an indirect. If you used no hot water, the boiler would probably still fire 3x a day for about 10 minutes to maintain the indirect's tank temperature.
    The second best thing to do would be to change the aquastat to something like a Hydrostat 3250 Plus. It has an option for circulator hold off, which keeps the circulator off when the boiler temperature is under 110. Also has some other options like thermal purge, and if you change the well, LWCO. You can even add ODR, but not very effective with oil. Without a buffer tank, you’ll short cycle a lot.
    I’d give them a call and tell them your concern, and if there’s no real reason, turn the low limit all the way back down, or off, if possible.
  • cdvo871
    cdvo871 Member Posts: 6
    edited November 2021
    He didn’t clean it - I don’t think he ever opened it up; just performed some basic maintenance, changing oil filters, etc.

    Aqua stat is Hydrostat 3250 - not the Plus. I’m pretty sure it does already have a LWCO.

    Not sure what your mean about the indirect - we have a separate electric water heater for domestic hot water.

    He did say that the boiler running to keep the temp at 140F without a heat call wouldn’t run the circulator - but I do feel the house getting a bit warmer even though the boiler only runs a couple minutes, and circulator pump supposedly isn’t running.

    I’ll give them a follow up call and see what they say.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,368
    I misread separate DHW, for indirect.
    3250 plus is the only one they make.
    Download the instructions. You can change low limit to off, and turn Circulator Hold off to 'On'