Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

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: 1,868
    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 AlaskaMikeAmann
  • SuperTech
    SuperTech Member Posts: 2,126
    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: 5,756
    What are the aquastat and mixing valve settings?
  • rick in Alaska
    rick in Alaska Member Posts: 1,452
    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.
  • Lance
    Lance Member Posts: 258
    To guarantee hot water to remain hot you must restrict cold flow to the GPM of the coil. Often done with a fixed orifice, subject to water pressures. This input can be increased by raising the temp of the coil and adding a tempering valve for the mixed temp you desire. A limited short term demand solution. Any uninsulated hot water pipe is a heat emitter. It should be insulated. To achieve a rated GPM at the faucet the boiler must be capable of providing that input for all the temperature losses. Generally a steady 3 GPM demands at least 199,000 btuh. OF course this can go up or down depending on the temperature differences of the water. To achieve a short term demand with lessor btuh, a storage tank can help.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,600
    edited August 2022
    I can almost guarantee you that the original installer did not follow this piping arrangement on your Tankless Coil water heater. This is because, out of several hundreds of tankless coil boilers I have serviced over the years, I have only seen a hand full of them piped properly. And my hands are not that big. The rating of your boiler's water heater is 3.25 Gallons Per Minute (GPM) intermittent. That coil can supply 3 GPM constant flow if you maintain a steady boiler temperature. And I will bet that your shower uses more than 3 GPM.

    To check this, get a stop watch (there's an app for that) and a 5 Gallon bucket. Using a 1 gallon container, add 1 gallon of water to the bucket. Mark that level with a permanent marker. Add another gallon and mark that lever. Add a third gallon and mark that level, Then, using a 1/2 gallon container, add 1/2 gallon and mark that level. Continue until the bucket is marked to 5 Gallons.

    Take that bucket and turn only hot water in the shower. Simultaneously, and at the same time, start the stop watch and put the bucket in the shower to collect all the water from the shower nozzle. After 1 minute time has lapsed, look to see if the bucker is full to 3 Gallon mark. If the bucket has more than 3 gallons (or overflowed) at 1 minute, then you are using hot water faster than your heater can make it.

    You will need to adjust the amount of water thru the water heater to 3 GPM or less, in order to maintain a constant hot water flow.

    This illustration is from a popular mixing valve that I used over the years. Notice that there is a thermal trap in the piping design as is also illustrated in the Weil McLain instructions
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,248
    Hi, I've been to troubleshoot a "not enough hot water" job where the heater was being blamed. I "wandered outside of the boiler room" and measured flow from the showerhead at 8 gpm. No wonder they were getting short showers! Anyway, low flow (2.5 gpm or less) showerheads can do a lot to help water heating equipment behave. In this case, if 70% of the 2.5 gpm flow is hot, that's 1.75 gpm of hot. The tankless coil should have no problem with that, even when the teenager takes a 30 minute shower. :)

    Yours, Larry
  • HomerJSmith
    HomerJSmith Member Posts: 2,406
    Does the Lav in that bathroom put out hot water at a temp that you want? Run it and see if you run out of hot water in the same way as the shower. What are the other faucets doing. If so, problem probably lies with the boiler setup or mixing valve somewhere in the sys. What is the hardness of the water?
  • hot_rod
    hot_rod Member Posts: 21,878
    how old is the boiler? Has the coil ever been delimed?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream