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New baseboard loop heating when no call for heat

vilord Member Posts: 48
Good day everyone!
I hope you are all staying safe and healthy, I can imagine it must be tough these days!

We had a new boiler installed in the fall (a buderus G115/5, to replace our leaking Burnham V7).
Our system used to have baseboard *and* a fan coil air handler with leaky ducting *and* in-slab radiant for the inlaw apartment.

With the new boiler install, we also had all of the ducting and fan coil ripped out and baseboard installed, so the main house is 100% baseboards (we left the radiant loop alone).

Unfortunately, we found that the new baseboards were heating up the house when the DHW indirect was heating up. We called our installed back, he found that some amount of the DHW return water was running backwards through the baseboard loop instead of going to the boiler. He installed some sort of check valve near the return. That solved it... mostly.

But the new zone (Zone 1) still seems to heat up without a call for heat from that zone. I think now either the water is convecting or there's another reverse problem, it seems to happen when Zone 2 or 3 calls for heat.

I can call the installer back, but he seemed confused about what could be happening. Each zone is separately pumped by a taco 007 with internal check valve.
The 007's are installed on the hot side, pushing hot water up, instead of pulling cold water down (this i guess is more common these days?)

Any ideas what to do? As mentioned, the installer seemed like he was grasping at straws, so I'd like to hear from some others before bringing him back in.

Was it just plumbed badly? Or maybe the 007 has a bad check valve (is this common on new units?)

Attached a couple of annotated photos, sorry the plumbing was done in a way that makes it hard to photograph.


  • Grallert
    Grallert Member Posts: 649
    It is a bit hard to get a handle on from the pictures. The this to do is sit with it while the different zones are calling and really narrow it down the a zone and a culprit. It's very possible that you have a stuck or dirty internal flow check in the zone #1 pump.
    Miss Hall's School service mechanic, greenhouse manager,teacher and dog walker
  • dopey27177
    dopey27177 Member Posts: 887
    Some times circulating pumps are a bit over sized for the purposes intended. That being said water returning to the boiler may have just enough extra pressure to back feed one or more zones. Or there may be a piping problem that can cause this senerio.

    The best way to prevent a back feed is to put check valves in the return of all the zones close to the boiler return inlet.

    I say this because there should be a flow control valve after each pump. The flow control valve is and acts like a check valve,