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thermostatic mixing valve TMV not working with new tankless combi boiler.

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geofear
geofear Member Posts: 20
in Thermostats and Controls

I have recently installed a new Navien tankless boiler, which is working fine.

I have in a back bathroom a TMV mixing valve which does not appear to work with the new boiler. I have just replaced the valve to no avail. It makes no difference how I adjust the valve, max, min, or anywhere in between, I get no hot water, AND the tankless shows no DHW flow thru the status screens. (only this faucet, which is after the mixing valve, behaves in this way). The cold and hot lines are not reversed.

It appears to be a flow issue thru the valve ???

Thank you for any thoughts you might have.

PC7060

Comments

  • Big Ed_4
    Big Ed_4 Member Posts: 3,531
    edited April 20

    It seems to be a bypass .. cold water bypassing the boiler .. Bad facet or shower body ,any connection upstream from the boiler will cause that issue.. Shut off the cold in that section and leave open the hot .See what happens , if it gets hot …bypass..

    There was an error rendering this rich post.

  • tcassano87
    tcassano87 Member Posts: 144

    what kind of mixing valve is it and how many GPM does it allow through? What does the flow look like its possible that it might be so minimal that it’s not picking it up. Especially when mixed with the cold water
    have you tried removing the mixing valve and running the faucet without it?

  • pedmec
    pedmec Member Posts: 1,383

    when you open the faucet the mixing valve is seving check how many gpms are flowing thru the water heater. There should be a menu parameter on the screen of the water heater to show you the GPM's. which model navien do you have?

  • pedmec
    pedmec Member Posts: 1,383

    Navien needs a minimum 0.5 gpm flow to trigger ignition. it can be adjust a little lower

    bjohnhy

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