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Pumps in series

rx7145 Member Posts: 7
edited February 2019 in Strictly Steam
I have three zones on the hot water boiler. One zone is a in floor radiant heat with a mixing valve and pump. When just the in floor zone is calling for heat both pumps are running but very little water is being pumped by the main pump do to the mixing valve. Is this a problem?

I’m also having trouble keeping the radiant floor loop cool enough. The mixing valve is set at 110° but I’m seeing output as high as 140°. Is the valve bad or is the dual pump setup causing this problem?


Pictures here: https://photos.app.goo.gl/7mnVeyxvDJnR84446


  • GroundUp
    GroundUp Member Posts: 1,654
    Looks like both the hot and cold side of your mixing valve are piped to the boiler return and the red handled valve is closed so there is no way to temper it any further. The return from the floor needs to be piped to the cold side of the mixing valve, not the return from the high temp emitters
  • rx7145
    rx7145 Member Posts: 7
    I’ve added a picture showing the hot/water lines. It seems to me it’s plumbed correctly.
  • DZoro
    DZoro Member Posts: 1,048
    The main boiler pump is forcing water into the mixing valve. If you were to fully open your boiler bypass valve it will act as a pressure relief to the mixing valve and allow it to work properly. I would also suspect ghost flow was a issue? The radiant recently added?
    Open the valve you have fully closed, that should allow the excess hot water to return to the boiler.
  • mikeg2015
    mikeg2015 Member Posts: 1,194
    I’m having trouble following it. But the mixed water off the mixing valve needs to go to the pump suction. The expansion tank and strainer should be located after that at the pump suction. The hot side of the mixing valve goes to the “return” loop on the cold side connect to the return on floor loop and has a T and then is piped to the Return header.

    There should be closely spaced T’s for these 2 connections. a maximum of 2 pipe diameters and located 10 pipe diameter from any elbows on either side. SO they should be 1-1/2 - 2” apart and at least 10” from any elbow on a 1” header.

    For the rest of the system, it looks like the zone valves are on the return piping. Is that what I’m seeing.

    Might be worth drawing this out and learning to sweat pipe. Then buy a sheet of plywood, some unistrut, pipe clamps and go to town building a new header this summer. There’s plenty of examples of an injection zone combined with multiple non mixing zones.

    Another solution is to remove all zone valve and use only zone pumps. (Less issues that way). then pipe it as a primary and secondary and use remade manifolds with balance valves. That’s my preference.

    Not to over complicated it, but if your going ot do it, do it right. You NEVER see pre WWII year old pipeline that looks like that.
  • icy78
    icy78 Member Posts: 404
    Unrelated but...is your water heater flue running downhill from the heater to the elbow in the corner? If so, thats dangerous. Should rise 1/4" per foot.
  • GroundUp
    GroundUp Member Posts: 1,654
    Looking at the new evidence, it looks like the zone valve in the vertical pipe opens on call for heat from the floor to allow hot water to the mixing valve? As has been mentioned, your main circ is then pushing into the hot side of the mixer and nowhere else which is screwing with the thermostat in the valve. The only right way to fix this is a repipe IMO, but I think you could put a band-aid on it by throttling that blue handled ball valve in that loop to make the flow rate through the floor loops higher than the flow rate through that blue handled valve to allow the floor pump to suck the mixed water through the mixing valve instead of trying to force it into the hot port
  • rx7145
    rx7145 Member Posts: 7
    Thanks for all the replies. I have cracked the valve for the boiler return to the hot side of the mixing valve. This seems to have dropped the temperature and the other zones seem to work normally. I’ll look into a partial replum. I don’t think I would need to change a lot.