At wit's end with broken hydronic heating system

Discussion in 'HVAC Heating & Cooling' started by TGL11, Dec 14, 2007.

  1. TGL11

    TGL11 New Member

    Messages:
    2
    Hello there, I'm hoping that someone here can give me some good advice...

    I've had no heat for over two weeks, despite four visits by a heating/plumbing repairman and $2000 spent on services.

    Here's the problem. My hydronic heating system will work for about an hour tops, while the air coming from the vents slowly turns cooler and cooler until nothing but cool air comes through. I've also noticed that I can only get warm air from the system again if I let it "rest" for at least 12 hours, and then I get the same thing again: It'll produce warm air for about an hour tops, during which time the air becomes cooler and cooler until I'm running the equivalent of an airconditioner in the dead of winter.

    Thus far, I've had the the following items replaced:

    • Two check valves
    • One thermostatic mixing valve
    • One hot water coil unit

    Addtionally, the system has been drained and purged several times, the motor has been checked and confirmed as good, and there's nothing wrong with the hot water heater; it was installed new less that one year ago.

    At this point, I am weary of spending money on something that doesn't seem to get fixed...

    Any ideas?

    Thanks in advance for your help,
    ~ TGL
  2. leejosepho

    leejosepho DIY scratch-pad engineer

    Water heater or boiler, and are you sure it is big enough to do the job?
  3. cattledog

    cattledog New Member

    Messages:
    42
    Location:
    Portland, Oregon
    TGL11--

    Please give us some more information about your system, especially the heat source, the hot water circulation to the air handler, and the control system. Also, what is the heating load the system is designed for. The air side of the hydro/air system you describe does not sound like its a problem.

    It would appear that when you get a call for heat, the sytem works correctly at first with hot water reaching the air handler, but can not bring the space to temperature and the heat source can not keep up with the demand. What is the boiler/water heater doing when the system is blowing cold air? The "goes to cold with a 12 hour recovery" is troublesome. It does sound like you are using a water heater (gas? electric?) with a storage tank, and the fact that the water heater is new, does not guarantee that it is still working properly and has the recovery time needed.
  4. TGL11

    TGL11 New Member

    Messages:
    2
    Thanks to leejosepho and cattledog for your responses; they are much appreciated.

    To answer your question(s): The hydronic heating system is run from a gas-powered 50-gallon hot water heater complete with expansion tank. The hydronic heating system is tasked withing heating my a 1100-square foot condo, a single-storied unit on the top floor of my building.

    UPDATE: The heating/plumbing company that I've been working with decided to try something that seems to have fixed the problem: They replaced the circulation pump. They surmized that my former pump would work for about an hour, then overheat and lock up.

    Now that it's been over an hour since they installed the new pump, I am happy to report that the air that's been coming from the vents has been consistently warm. I'm going to keep my fingers crossed that the warm air continues.

    Thanks again,
    ~ TGL
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,032
    Location:
    Cave Creek, Arizona
    ?

    Why wasn't the problem diagnosed properly before they started changing parts? That is the most expensive way to repair anything, from automobiles to heating systems, and every thing in between.
  6. cattledog

    cattledog New Member

    Messages:
    42
    Location:
    Portland, Oregon
    I'm in agreement with hj, and your heating/plumbing company has some explaining to do. This is not rocket science.

    You told them the system was failing within an hour of turn on. It should not have been too difficult to arrive when the system was in failure, and they could have determined there was a call for heat, the pump was not circulating hot water to the air handler, and the water in the heater was hot and the heater off. It's not even a stretch to say that they could have watched the 1 hour cycle from turn on to failure. They would have focused on the hot water circulation and and all the relays, pumps, valves, mixers, etc involved in getting hot water to the air handler.

    The replaced hot water coil (the unit in the air handler, I assume) is particularly troubling. If the coil were plugged, why did the system work for an hour at a time?

    On the other hand, I'm curious about a 12 hour thermal lock out of a pump motor. Some motors have a manual reset, others are thermostatic. Was your statement about the 12 hour recovery period accurate? Do you know the make and model of the circulator? It would be interesting to know if there is some sort of unique thermal protection. I would have expected the system to be cycling on the pump cut out or to be shut down expecting a manual reset.
  7. leejosepho

    leejosepho DIY scratch-pad engineer

    Whew! Like the others have essentially said and as you had already been experiencing, that is a terribly expensive way to eventually stumble across a bad pump!

    Maybe you should let the condo association know about those parts changers pretending to be mechanics -- true mechanics know which part(s) to change -- so other residents can be warned to steer clear of them.
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