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Eternal on-demand water heater

Installed an Eternal GU 145S in 2011 and now has an error message: "E27" - mixing valve issue.  Tech support says the mixing valve has gunked up and needs to be replaced.  Has anyone else had problems with these?
Often wrong, never in doubt.


  • Harry TuttleHarry Tuttle Posts: 1Member
    Seen this a few times...

    I have encountered that error and replaced the mixing valves a number of times on a few of those units.

    A question; how is the unit being used? I ask because on the units that I replaced them on where set up as a boiler for radiant floors rather than as tank less water heaters. According to the tech support person, they stated that those units are not designed to run like that, and the constant flow from the circulator causes cavitation, or something to that effect on the mixing valve. This causes the mixing valve to become "noisy" and the control board shuts down the unit.

    On those units, I ended up piping the radiant floor side to a plate heat exchanger, and added domestic to the outlet of the Eternal and so far the units are working normally again, and no call back for mixing valve issues. (One unit I replaced the mixing valve 3 different times until the tech support advised me that it could no be used as a "boiler")
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