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DHW Overshoot, Capacity / Step Modulation

I would like to maximize the efficiency from my HTP UFT-80W.
I notice that when DHW calls it overshoots the target 180F and gets up to ~187F before the boiler modulates down. Right now the burn time is a few min long and even with a tiny 20Gal DHW tank it recovers fine so we have not run out of hot water.
There are some settings I could use to prevent the overshoot but it feels like limiting DHW Capacity, lowering target temp or turning on Step Modulation would just slow-down hot water recovery, would that be beneficial in some way? Am I missing something?

Thanks for any advice in advance,


  • mattmia2
    mattmia2 Member Posts: 9,398
    You can lower the temp for the dhw call, the lower the return water temp, the more efficient the boiler will be. The return temp needs to be around 130 degrees to condense the water in the flue gases and get the claimed ~95% efficiency. at the 180 degree temp for the dhw call the return temp is likely not causing any condensing in the boiler and you are getting around 85% efficiency. you can reduce the temp until it doesn't keep up then turn it up a bit. the longer cycles it runs at a lower temp the more efficient it will be.

    I'm not sure how effective the step modulation would be, it would make more sense for it to modulate on rate of change than on time.
  • mattmia2
    mattmia2 Member Posts: 9,398
    I was running mine at 140 all summer without running out but I have a 40 gallon indirect. Now that the incoming water is getting colder I have had to increase it to 150.