I am working on the theory that any hot water that is available from the solar system will pre-heat the water going into the Gas Boiler, but the elctronics and the modulating valve in the gas boiler will control the final output of the system. Obviousley it cannot cool the water, if the output from the solar system is hotter than what the temperature is higher than the setting on the gas boiler, but I can live with that. What are your thoughts?

  • That is the usual way, only use the gas to keep the water hot when the solar does not.
    – crip659
    Commented Dec 27, 2022 at 21:39
  • Will need to be careful if water temperature is above 120 degrees if young children/old people use it if no anti-scalding valves used at the faucets.
    – crip659
    Commented Dec 27, 2022 at 21:50
  • Do you directly consume the water going the the solar system, or does it have a coolant fluid (like your car's radiator fluid) that then goes through a heat exchanger to heat the actual house potable water supply?
    – FreeMan
    Commented Jan 27, 2023 at 14:41
  • Sanity check: are you talking about using solar to heat/preheat the water heater, or a forced-hot-water heating system?
    – keshlam
    Commented Jan 27, 2023 at 15:43

1 Answer 1


Check your gas boiler specs, to make sure the solar will supply enough pressure and flow.

Usually solar heaters have low flow and low pressure which will not work well for the gas heater.

  • Also, what happens in winter? Is the solar water heater drained, if it gets cold in your area? Commented Dec 29, 2022 at 2:07
  • In most places, @DrMoishePippik, the sun also shines in the winter...
    – FreeMan
    Commented Jan 27, 2023 at 14:39
  • 1
    @FreeMan shining is not the same as producing sufficient heat to keep pipes from freezing -- specially at night time. Commented Jan 27, 2023 at 19:40

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