Tankless water too hot for first minute - is this normal?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Mike_J, Feb 22, 2005.

  1. Mike_J

    Mike_J New Member

    Messages:
    6
    Location:
    Boston area
    I understand why hot water tanks can deliver water that's hotter for the first minute or so (heat rises to top of tank), but I have tankless hot water from an oil burner and for the first minute the water is very hot (160F) and then sometimes drops down to a much cooler temp (as low as 130-ish) but eventually settles down to about 145F and stays there. Is this sort of behavior normal from a tankless? If not what could cause this? We have a Watts Regulator mixing valve at the boiler that is set to the hottest setting--any chance the mix valve is too old and not working right?

    Mike J.
    Boston
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,258
    Location:
    New England
    yes...also, it takes a moment or so for the tempering valve to react. Last, it could have heated up some of the nearby water, so there is not much cold to actually flow to temper it for a moment. Unless you are in a commercial situation, over 130 is risky. My unprofessional opinion.
  3. Mike_J

    Mike_J New Member

    Messages:
    6
    Location:
    Boston area
    Thanks for the feedback. In considering your idea about the water in the cold pipe being heated, it suddenly occurred to me why the initial water is so hot. Tankless has no thermostat--the water is heated by simply passing through the coil, and when you aren't running the water it sits in the coil getting hotter in hotter as the furnace runs to heat the house. Between that and the two extra things you mentioned it' so obvious I'm embarassed I had to ask :)

    I totally agree--I think the mixing valve was turned all the way hot because the shower was too cold, which I fixed by simply adjusting the max temp limiter on the shower valve (previous owner should have read these forums before trying to fix things himself!)
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