Circulating pump not moving water to air handler

Discussion in 'Maintenance and Troubleshooting' started by TimF, Nov 5, 2013.

  1. TimF

    TimF Member

    About a week ago, I was heading outside when I heard a noise which I thought must have been a squirrrel trapped somewhere in my basement. It turned out one of my two air handler circulating pumps was the culprit. The fitting on the input side of the pump was slightly warm (buffer tank = 90F) but the output fitting was stone cold. The pump motor casing was very hot. I checked the other circulating pump which was running at the time and both input & output fittings as well as the pump motor casing were slightly warm. I shut off the thermostat to the very intermittently squealing pump and let it cool down for several hours while I worked outside. Later that afternoon, I turned on the pump and it worked fine. I ordered a replacement pump (Grundfos UPS15-58FC) just in case. For the next 6 days the pump has run circulation problem and no noise. At this juncture, although the pump motor runs, the pump has failed to circulate water for the past two days regardless of how long between attempts.

    The replacement pump is being delivered today and I'm a bit concerned as I need to improve my chances for a complete fix as I have to leave town for three weeks this coming Saturday.

    My questions/concerns are:
    1) Is the pump itself the problem or simply a symptom of another problem?
    2) Is there anything I should be checking for before or during my replacing the pump?
    (I can isolate the pump by shutting off the valves on the input and output flanges)

    Thanks in advance for any insight, comments, suggestions.

  2. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Pump motor casing very hot = air in lines.
  3. TimF

    TimF Member

    Thanks....I'll look for air in the line. The output line of the failing pump does go vertical about 6" then makes a downward U-turn for about 3 feet via two 90 elbows. Since it is the first pump, it is altogether possible any air in the line coming from the buffer tank would get trapped there. Any air that makes it past the first pump would pass through the second pump enroute to the attic air handler. I suspect I'll need to look for air at the attic air handler as well since the line goes straight to the attic.

    I know there are no purging or fill ports in the external plumbing between the either circulating pump and their respective air handlers....should there be or do the airhandlers themselves typically provide air purging capabilities?

    Regardless on what I find for the failing pump in terms of air being trapped, I'm considering replacing the first 90 elbow with a T and then installing an Amtrol Float Type Air Vent (as I recall there was on my old oil fired hydronice boiler before the zone valvers) on a short vertical riser for added insurance. Your thoughts?

    Thanks again for your input.

    Tim F
  4. TimF

    TimF Member

    You were right on...I had a massive air blockage in that pump. I replaced the 90 elbow directly above the pump output flange/valve with a Tee and an Amtrol Float Air Vent. I then added Tees, ball valves and 4 feet of 175psi nylon reinforced vinyl tubing vertically on both the air handler input & output. Once I added about 1.5 gallons of food grade gylcol and bled the air out of the system using the two vinyl tubing setups, I cracked the pump output flange bolts, at which time the pump started pumping again.

    This is a closed, non-pressurized system (comprised of a HP, 65 gallon buffer tank, 2 circulating pumps & air handlers) which doesn't have an expansion tank. The system is two years old and was originally commissioned at the start of the 2011 heating season. The system has just gone through it's fourth season change (initially heat then cool then heat then cool and now heat). I'm thinking that the air problem could be due to the lack of an expansion tank to handle the contraction and expansion of the glycol due to the seasonal changes in water temp ranging from 50F - 110F. Does that make sense?

    Thanks again... It's nice having heat and three days to watch things before I leave.

  5. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    If it is truly an open non-pressurized system I do not think an expansion tank would help much. The question is how is the air getting in the system. Is the buffering tank equipped with an air vent?

    Chris thought air, I though trash eating the pump impeller.

  6. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    I'm not sure we've got the full picture.

    A radiant system is not too often closed (it has makeup water) and non-pressurized (it is pressurized). If yours is, you definitely need an expansion tank to deal with water temperature changes (and the resulting pressure changes).
  7. TimF

    TimF Member

    Mark and Chris,
    My apologies if I haven't explained the environment very well. I think of the system as a closed system because unlike a hydronic system which allows makeup water to be added through a pressure reducer or a system whereby some part of the system is open to the atmosphere, my geo system is neither of those. Basically my system centers around a 65 gallon buffer tank which is nothing more than a standard elctric water heater without the electrodes hooked up. The heat pump circulates water through the buffer tank via it's own, dedicated pump. The two air handlers are fed by their own ciculating pumps. Other than the standard pressure relieve valve on top & a hose bibb valve at the bottom of the buffer tank, there is another hose bibb on the line from the HP to the buffer tank. Yesterday I installed valves and hoses at the input and outputs at the attic air handler in order to be able to purge the air from and add glycol to the system.

    I hope this helps clarify...thanks for your interest and suggestions.
  8. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    OK. Makes sense. But yes, if I was called in, I would be recommending an expansion tank and makeup water. As it is, your system will end up with air in it as water blows the pressure relief valves when heated. These two, can be plumbed wrong so there is a bit more to it than just slapping them in.
  9. TimF

    TimF Member

    I recently added expansion tanks on the cold supply side to my DSH buffer tank and to my primary hot water tank where there are no valves or check valves between the expansion tanks and the water tanks. I can do the same with the geo buffer tank. I'm assuming a 4.5 - 5.0 gallon boiler expansion tank would be sufficient for a 70 gallon system at temps between 50F - 110F.

    I do still have the pressure reducing valve from my old oil fired boiler that I could plumb in for make up water. As I recall, I think it provided 10 - 12 psi. I could install it and test the pressure before setting the expansion tank pressure.

    Thanks again for bailing me out!

  10. mtrentw

    mtrentw Active Member Industry Professional Forum Leader

    Why glycol in a system with a temp range from 50-110??
  11. TimF

    TimF Member

    The attic air handler is subject to sub-zero temps (-15F last winter). The supply and return lines to the attic air handler are insulated, however, there are times when the air handler won't be called into action for an hour or longer.

  12. mtrentw

    mtrentw Active Member Industry Professional Forum Leader

    Makes sense. While it is very likely you'd cycle on frequently with temps that low, before water had a chance to freeze; a power outage, temporary shutdown or T-stat setback could leave it stagnant and freezing before too long. One of my two units is an attic unit and while I've got a glycol system and won't see attic temps much below 5-10 degrees, I do have DSH lines that give me some concern. Tried to insulate the bejesus out of them and hope they run enough to prevent a freeze. I am somewhat relying on the resiliency of PEX to freeze thaw cycles if it ever does occur.

Share This Page