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Radiant Heating - Taco Pumps Ran Dry for Few Hours - #30 Pressure Relieve Valve Popping Off Now

cloves Member Posts: 16
We have a closed radiant heat system and the supply to the pumps was turned off overnight and the thermostats called for heat. The following day when I got home I heard the pumps and they didn't sound right so I shut off the system. I checked the radiant side of the system and it was almost bone dry at one of the outlet valves. I proceeded to evacuate the air out of the system and then tested to see if pumps were still working ( I had flow when thermostats called. I noticed that pressure gauge (On the radiant side), which never has passed 12psi was now running higher 18+. Today I noticed that the #30 pressure valve was going off enough to fill a half bucket of water.

Water supply has been turned back on but something is clearly wrong with the system. We have a Taco 008 SS on the water side and a Taco 011 iron on the radiant side. Yes, they are high head pumps because our radiant guy was a moron who oversized the pumps. But that's a whole other issue.

Anyone have any insight on what could be causing the excessive pressure? The radiant side of the system is the one popping the #30 relief valve. I suspect my Taco 011 is damaged and causing excessive heat but having trouble wrapping my head around the why. The system uses a heat exchanger and since the supply side was the one starving for water not exactly sure if the problem is Taco 008 instead.


  • Jamie Hall
    Jamie Hall Member Posts: 18,949
    First thing to do is to check the expansion tanks(s). Then check any automatic water feeders.

    A damaged pump -- which is quite possible -- will not cause excessive pressure.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • GroundUp
    GroundUp Member Posts: 1,405
    A picture of the system would be very helpful. With the pumps off, static pressure should have been back to 12 where it was before. Did you fill the system manually or is there an autofill? Why was the radiant side low on water? Do you have a visible leak somewhere? Is this an open system of some sort or what do you mean by "water side"?
  • pecmsg
    pecmsg Member Posts: 2,896
    Have you found out why you lost water in the radiant?
  • Gordy
    Gordy Member Posts: 9,514
    edited November 2019
    First you have to find out why you lost system fluid in the first place.

    Prv popping off.

    Sounds like system is open, or non barrier tubing was used in the boiler side since a ss circulator, and HX is installed.