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Heating loop zone returns not getting hot

JaySyd Member Posts: 22
edited October 2022 in Radiant Heating
Hi guys, hope everyone is great. Read through quite a few posts on here and learnt a tonne together with YouTube on best approaches to purging my system of any air first and foremost. That solved an issue with a couple of zones on the higher floors (thank you gravity!) , but with a couple of remaining zones I'm unable to get any water to come back around the return.

In the attached image, I labeled the zones as 1 and 2. Zone 1 goes one floor up to the laundry room floors and zone 2 to the same floor as the boiler which is our the basement floor.

Zone 1 is getting hot on the pump side but not on the return (seems like the pump is on the supply and not return side) and the basement (zone 2) is barely getting hot on the pump side and nothing at all on the return.  With zone 2, it looks like the pump is connected to the cold side of the thermostatic mixing valve and pushing that cold water through the loop. 

The system doesn't seem to have a filling loop installed to use (from what I can see) , so I'm not really sure on the best approach to doing it except using the bibs that are there for Flushing/purging the system. 

We bought this house from someone else so before calling a pro, just wanted some advice on some things i can try. 

Also added some extra images at different angles of the lower part of the system which has the circulator for the basement. 

Another question that I was curious about - is the return on under floor radiant heating always supposed to be cold-ish? or should it eventually come up to the same temp as the supply?

Appreciate any of your help peoples!


    HVACNUT Member Posts: 5,765
    Looks like there's a pressure reducing valve directly under the boiler. However, with the pic I can't make out the piping. Looks funky.
  • JaySyd
    JaySyd Member Posts: 22
    edited October 2022
    The pressure reducing valve under the boiler is connected to the auto-Feeder from the street cold supply that goes into the boiler with a back flow preventer just before it. The picture is a bit deceiving since it looks like that valve is in the heating loop setup, but its not - its just in front of it.
  • hot_rod
    hot_rod Member Posts: 21,898
    Something seems off with that piping. There needs to be a circulator on the M "mix" port
    sometimes called AB, of that 3 way valve for it to work properly. It pulls flow from H&C to blend.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • JaySyd
    JaySyd Member Posts: 22
    edited October 2022
    Thanks @hot_rod much appreciated. I see what you mean. The circulator is on the cold return side of the loops in our instance - why on earth would they do that? Could it be anything to do with the fact that gravity isn't really an issue here given the runs are on the same floor as the setup and pressure alone could be enough? From touching the pipes, it seems as though the circulator is circulating cold water into the mix

    What I think may have happened before we bought the house was that they added an extra zone (the basement zone) to the whole system as a branch of one of the 1st zone I labeled on the pictures above - since the hot supply to the basement comes off the 1st zone supply and the return segment of the basement comes off the return of zone 1.