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Aquatherm Combo Air Handler Water issue

TerryK Member Posts: 3
edited November 2020 in Radiant Heating

I tried to search for this problem but only found matches that were close to my problem.

Here goes. I have a brand new Aquatherm AC/Heat air handler that is piped into the complexes main boiler system which is shared with 20 other condos. I called them back for this issue, but they are scratching their heads... which is concerning. They even had to repipe the inlet and outlet pipes after the install because they plumbed it backwards. In plumbed into the Out and vice versa. I wasn't impressed but it was in and looked nice enough.
Anywho... The heat works fine. Water going through the pipes is at a good solid 120-130 degrees and 95 degrees coming from the registers. But when I turn on the AC, it still blows warm air. Not quite 95 degrees but not cold.

The air handler pipes are hot when the AC is on. (cooler on the return side and scalding hot on the inlet side) But when both systems are off and nothing is on, BOTH pipes remain scalding hot.

My assumption is that the hot water is flowing all of the time in both AC and Heat modes? My other assumption is that I would think the hot water should shut off unless it's in heat mode, right?

When I turn off the isolation valves at the wall, the AC blows ice cold. (The entire system has been replaced so the AC works great.... but it doesn't like to switch from Heat to Cold unless I turn off the hand valves.


  • TerryK
    TerryK Member Posts: 3
    Oops, somehow a few of the pictures weren't uploaded for some reason. Probably do something right on my end.

  • mattmia2
    mattmia2 Member Posts: 8,446
    If you turn the power off to the unit do the pipes stay hot? It is either that circulator isn't wired to only turn on when there is a heat call or the pressure difference between the supply and return is enough that it will open the flow check and flow through the pump regardless of if the pump is running or not.
  • Jamie Hall
    Jamie Hall Member Posts: 21,573
    I am not familiar with this unit, but a thought does occur to me. Is this set up to provide dehumidification as well as air conditioning? If so, what should happen is that on AC it should cool vigorously -- and then it should reheat to the desired temperature. if it is supposed to do that, is it doing it properly?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 6,175
    edited November 2020
    Two possibilities. One is what @mattmia2 said. the flow check is passing, or it got damaged during the piping and repiping or it is not even there. so with all electricity to the unit off. there should be no heat in the pipes near the unit. This may take a few hours to verify. You have to see it the heat goes away after 4 to 5 hours.

    I have seen this problem repaired with a zone valve added to the piping and the room thermostat operates the valve and the valve end switch operates the fan.

    The second is the wiring! is the control wiring keeping the pump operating all the time the electricity is turned on to the unit. If the pump is running 24/7 then the pipes will be hot all the time. Get the control wiring/system fixed.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • TerryK
    TerryK Member Posts: 3
    Thanks all. I will check all of those things and report back late tonight. :)