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Waiting a long time for hot water, then water doesn’t stay hot for long

Hoping this something simple. Weil-McLain wtgo-3, oil fired, isn’t delivering hot water right away to 1st or 2nd floor showers, waiting as long as 5 minutes,
then water doesn’t stay hot for long,about 5 minutes before shower goes warm. All faucets seem to be fine. Base heaters seem to be providing plenty of heat. Turned the high and low temps up, maybe helped a little but still having issues. What could it be ? ( no experince with this, but always been a DIY kind of guy), any suggestions ?


  • GroundUp
    GroundUp Member Posts: 1,406
    Indirect coil in the boiler I assume? Do you have a mixing or tempering valve on the output? Could be a bad mixer or a plugged up coil, has the coil been cleaned recently?
    rick in Alaska
  • SuperTech
    SuperTech Member Posts: 1,792
    I can't be sure of anything based upon the information you gave us, we need to know if you have a tankless coil or indirect tank.

    But from the sound of it I'm going to guess you have a tankless coil that might be full of hard water scale. You can have a pro descale the coil, but you really need to know how many times it was done before. The chemicals used are pretty nasty, I don't recommend trying this too many times.

    If you have a tankless coil the best thing you can do to assure you don't run out of hot water is to install an indirect tank. These are better suited (but not immune) to hard water conditions. The best thing about it is you could save up to 10-15 percent of your fuel costs, since you will no longer need to keep the boiler hot 24/7 365 for the tankless coil.
  • tryan
    tryan Member Posts: 1
    I have similar problem with the upstairs renovated bathroom that has Delta Shower valve with anti scalding. Rough valveR10000, Faucet T11864. Coil in Boiler cleaned, mixing valve, pro plumber install. “Idle HW in the pipeline lasts 3 minutes followed by 12 minutes of sub 100 at the shower head until boiler starts up and then a great HW shower. (Adults here no kids) We’ve been tricking the process by calling for heat for our baseboard which of course results in a great HW shower. I don’t want to go this way as warmer weather is coming.

    Downstairs shower valve without anti scalding is VG. I can adjust the shower valve as needed.

    The boiler closet is jammed tight w no room for a tank at this point. I’d like to find a work around w the anti scalding system. Would adjusting the stops at the shower valve do anything helpful?
    HVACNUT Member Posts: 4,596
    What are the aquastat and mixing valve settings?
  • rick in Alaska
    rick in Alaska Member Posts: 1,362
    The WTGO is a tankless coil boiler, so most likely the mixing valve is messed up, or the aquastat isn't responding right, or both.