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Bad Tempering Valve ????

I recently had my oil burner serviced by my local HVAC company for the winter. During visit I advised tech that I was losing hot water to the house with the water being luke warm to cool. Tech checked out system and stated due to winter heat demands on the oil burner I was losing out on hot water and suggested a indirect hot water heater be installed. I have had this probelm before which was a mixing / temp. valve issue. I recontacted my HVAC company and they sent out the tech who replaced or repaired the mix / tempering valve. This did not correct the problem. I am getting extremely hot water out of the coil to the mixing valve. This was checked while the hot water was running while a family member was taking a cool shower. There was no loss of temp. coming out of the coil. After the mixing valve my domestic hot water pipes are warm but not hot. I don't think mix / temp valve was replaced, I think a repair kit was used by the HVAC company.


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    edited December 2019
    Depending on the type, if everything but the mixing valve housing was replaced, should’ve worked, if that was he problem. Maybe it wasn’t adjusted properly.
    What was the cold water temp going into the coil, temp coming out of the coil, and what was the temp after the mix-all at the start of the shower and a few minutes in.
    Coil could need flushing/boiling, and of course an indirect on its own zone would be best-usually endless hot water, and boiler doesn’t fire every time someone uses a little hot water.
  • wood1967
    wood1967 Member Posts: 2
    TY for your feedback - I think just the guts of the valve were replaced not the entire valve itself. The valve is a Watts 70AF. Didn’t get a actual temp on the pipes going in/out of boiler or after mixing valve just by touch of the hand. Newbie here - any suggestions on getting a actual temp - Could the replacement repair kit have been bad and can I try another one from one of the big box stores. If I opt to use another repair kit do I need to drain the boiler to work on it or can I just shut off the boiler and main water supply to the house and bleed out the water to the home ?.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,525
    edited December 2019
    Negative on the boiler needing to be drained. That pressure is separated from the domestic hot water. If the internal parts of the housing have any corrosion the valve may not seat properly. place a tray or bucket under the valve. Turn off the cold water inlet to the coil and open a hot water faucet upstairs. This will backflush the valve body when you take the mixing valve apart.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    edited December 2019
    Best to buy the whole valve, and replace everything but the body, if a visual inspection doesn't show any damage.
    The repair kit doesn't have all the parts as the full valve.
    Also, heat can kill them too. If you boiler is getting over 200° could (shouldn't) damage it.
    Make sure you adjust it properly.
    They usually give you a little stick on thermometer to adjust the temperature, or you could use a K-type clamp on with a meter, or a meat thermometer, in a cup, in the sink.

    If you're still not getting the temperature you need, then it's most likely the coil. If you are, then your next culprit could be the mixing valve in the shower.
  • Intplm.
    Intplm. Member Posts: 1,790
    Watts 70F.......This is indeed a "tempering valve" and NOT a "mixing valve."
    The 70f is older technology and will not work in the long run. The 70f unit needs to be installed, trapped, well below the coil or heat source it is serving. (and even if it is,
    there is no guarantee it will work, new or old.)
    These things are problematic as a rule and should not be used for domestic hot water needs.

    You need a "thermostatic" mixing valve like this one pictured above made by Honeywell. There are other companies that make these too. Caleffi, Symmons, to name a few.

    Get rid of the tempering valve! Install a true mixing valve. A "thermostatic" mixing valve similar to the one pictured.
    Do this and your problems of a cold shower will go away.
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,230
    Hello, One more thing I'd add is to actually feel the three pipes coming to the mixing valve. You will feel the cold line actually being cold if the valve is mixing cold water in. If you get basically the same water temp in and out of the valve (at hot and mix ports) then the problem is likely a cross connection elsewhere in the plumbing.

    Yours, Larry
    rick in Alaska