In current generation, high-efficiency condensing boilers, how much should the supply water temperature vary from its target or set point temperature (T-set)? I ask this because our brand-new, Rinnai M090C (propane) boiler shows a variation of almost 50 degrees F, which I think may be the reason it does not effectively heat our house. Today, for example, with an outside temp of 50 degrees F, our boiler displayed a set point temp of 165 degrees F. However, over a period of several hours, while our first-floor thermostat was set to 70 degrees, and continuously called for heat without getting satisfied, the boiler’s supply side water temperature cycled between a low of about 125 degrees and a high of 174 degrees, as measured by the boiler’s internal sensors. The total time of each “cycle” was about 6.5 minutes, with the boiler firing (“C.Heating Active” mode) during each cycle for about 1.5 minutes and idling (“CH Pump Overrun” mode) for about 5 minutes. Is this normal for the M090C, and could this be the reason it is not effectively heating our house?
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