QUESTION OF THE WEEK: The Mystery Of The Fancoil Unit

This Question of the Week comes from the Building Owners and Managers Association (BOMA) International Group on LinkedIn.

I have an issue in my building relating to one of my air handling units (AHUs). I was in the process of winterizing the fancoil units, and I noticed that one of them is not getting any flow in the hot water coil (even though I opened both the manual and control valves). There is hot water flow in the other fancoil units, but I don’t feel any hot water flow in the heating coil of the fancoil unit. Any answer or suggestions would be greatly appreciated.

Anthony Black
Building Technologist
Angus & Associates
Toronto, ON 


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This post currently has 3 responses.

  1. Steve Rippert says:

    First check and be sure the control valve is not plugged or otherwise non functional. Then try bleeding the coil in case there is an air lock. Lastly, check and see if the coil itself is not plugged with sludge. Open the return line and have a bucket handy to catch what comes out. Run til the water is clear.

  2. Bruce Langele says:

    If I were you I would first borrow or rent an infrared camera and do the same as before then scan it with the camera, which should you exactly where the hot water flow stops?

    It maybe a clogged strainer, a valve that failed or in the wrong position of a 3 way valve. The control valve could also be set to be N.C. instead of N.O. You can check by looking at the valve stem (with the acturator removed). If you can you may want to try back flushing from the return side by closing all valves and opening the strainer bottom. Remove the screen then slam open the return valve several times and see if any dirt comes out. After this, do the same with the supply valve while the return valve is closed and the strainer still open.

    If you have gauges on both sides of any fitting (valve,strainer etc) you can check for pressure drop. Also check any triple duty & balancing-circuit setter valves for proper settings.

    If the coil is very dirty I would make sure that your water treatment is being done correctly?

    You should write down the order that you do these checks for future reference in checking any other coils.

    I hope this helps you.


  3. nigel says:

    Hi Anthony,
    You didn’t mention any stab valve or balance valve.
    We have often found that the small orifice in these valves collects sediment over time.
    From your description, you have flow or presence of flow in the pipe.
    My suggestion is, with the manual and control valves open, then open/close, open/close the stab/balance valve to squeeze out any sediment and let the water push the sediment out of the valve.
    if this works, incorporate this into the service agreement with the controls or HVAC company to be done on all coils on a regular basis.
    Hope this helps.

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