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Hot water heat system pump not running

blargendarg Member Posts: 5
edited November 12 in Domestic Hot Water
Hello all- I've done quite a bit of troubleshooting on this and just want to make certain I have my bases covered. Here's the scenario:

Standard Taco circulator pump doesn't run. I disconnected this and connected it directly to 120v and it runs fine.

Looking at the aquastat(L8148E 1257) there was obvious blackening on the board at the base of the relay, so I replaced it with one my father had in storage- it *looks* fine, but can't confirm it *is* with certainty. 

Relay wasn't clicking over on the new one so I jumpered T to TV and the relay itself works(looks like I also need a new thermostat), I have 120v at Line but not anything at C1/C2. I wanted to test the thermostat wire, so I jumpered the ends upstairs- relay clicked over as soon as I gave it power again, but nothing from the pump. I read that the pump should cycle on with the boiler around 145F, but it makes it all the way to 180 and boiler turns off and nothing.  Boiler and damper cycle just fine and so I'm still getting heat from passive circulation. It's just the one zone- no valves.

As far as I can tell, there must be something wrong with this aquastat as well. Is there anything I've missed here as to why the pump might not be running apart from that? I'm accustomed to this kind of stuff but these systems are complex- just want to be sure before I drop several hundred on a new part. Thanks for any guidance you can provide.


  • neilc
    neilc Member Posts: 2,502
    can you post pictures? and controls, all in one,

    do you have a meter and know how to use it?
    known to beat dead horses
  • blargendarg
    blargendarg Member Posts: 5
    edited November 12
    how's this? and yes, have & can use multimeter
  • blargendarg
    blargendarg Member Posts: 5
    Adding photo of connections for replacement thermostat, connected as the previous one was. Blue wire connected to R which connects to terminal TV in aquastat, White wire connected to W which connects to terminal T in aquastat and that's it. Red wire is not connected at either end. Can confirm this causes the relay to 'click over' with thermostat setting above ambient temp

  • Big Ed_4
    Big Ed_4 Member Posts: 2,523
    It seems the basement bargain has issues . I like the roll of BX :))
    I have enough experience to know , that I dont know it all
  • blargendarg
    blargendarg Member Posts: 5
    Just in case the pump needs relocating, haha. Not my doing, but it aint broke- so there it stays!

    Fair enough- it's unlike my pop have a perfectly good backup just sitting around so it kinda makes sense. 
  • hot_rod
    hot_rod Member Posts: 20,725
    When the relay clicks and you see it pull in is there 120v on the pump?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • blargendarg
    blargendarg Member Posts: 5
    Good thought. I tested this several times both at the pump connection at the board and at the pump itself. There is often, not always, voltage there briefly. Generally anywhere from 1-20v for a fraction of a second before dropping back to 0