Hydronic Heat Zone heating when thermostat is off

BrianW83 · November 13

I have a seven zone Hydronic Baseboard system. It consists of three radiant zones, two baseboard and one hot water tank. This just started happening but my one baseboard zone which is in my master bedroom I can hear the water going through the zone when other zones are on and this one is not. I have the Taco 007-F5 on all the zones. I believe from my research there is no check valve in these pumps but it can be installed. This is the first year I am having this issue is this pump bad or is it something else. The third black pump is the one that is heating up and going to the master bedroom. I can tell you it’s not 100% boiling hot it’s just warm. My thermostat is set at 67 and the room is currently 72

mattmia2 · November 13

There should be a flow check in each of those circulators or somewhere else in each zone. Maybe the one for that zone is stuck open.

EdTheHeaterMan · November 13

In order for a system that is zoned with pumps to operate properly every pump loop needs a chacjk valve to prevent reverse flow thru the loop(s) that are not operating. The Taco 007-F5 pumps can have a IFC added on the job. The only conclusive research would be to open up the problem circulator and look at the inside of the pump to see the IFC.

You can close off these 9 valves (yellow oval and 2 arrows) to isolate all the circulator pumps. Then you do not need to drain the entire system, so refilling or purging the air out will me at a minimum.

BrianW83 · November 13

Thank you. You were 100% correct. I opened up just the two zones that are in my master one in bedroom one in bathroom and there was no check valve. So I got a check valve at the local plumbing store for Taco 00 series. It worked fine in the green circulating pump but would not work in the black one. Any idea if they make a check valve for the older black pumps? The piece would not push in. I just replaced the one with a green one but I have two more black ones. If I have to replace them it is what it they are 14 years old now. It’s weird I never noticed this in the past but I think it’s because at that time we had no kids and kept house colder. We keep the kids rooms warmer now.

mattmia2 · November 14

Different models use different flow check valves and some of the older castings don't have the groove for the valve machined in them. you can try asking taco.

You can also put a separate flow check valve in the pipe out of the circulator.

I think calefi makes a particularly nice one with a built in union for service although since you have the pump flanges you could just use and npt valve with npt adapters and use the pump flange to unscrew it for service.

There is a whole series of them although they are miscategorized on supplyhouse.com as check valves instead of flow control valves:

https://www.supplyhouse.com/Caleffi-304759A-3-4-Sweat-Serviceable-Flow-Check-Valve-Low-Lead

HVACNUT · November 14

The black ones don't accept an IFC. As far as I know, the black 007's are shipped with package boilers.

If you can get a press tool, you can install spring checks on the returns.

Screenshot_20251113_200959_Samsung Internet.jpg

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It's weird that this is the first year its happening. You're sure there's no check valves anywhere that we can't see in the pics?

What boiler is there? Does it have separate BTU outputs for domestic, fin tube, and radiant? It must have because I don't see any mixing valves.

mattmia2 · November 14

or sweat it

hot_rod · November 14

its nice to have a serviceable check, as we see stuck and plugged checks on HH with some regularity.

Ideally a check is 12 pipe diameters from the pump discharge, out of turbulent conditions

If you now or ever embrace ECM variable speed circs you want a check with a low “pop” pressure .35- .50 psi for small sizes

SteveSan · November 14

@mattmia2 Any 007-F5 manufactured after 2006 should have the ability to accept the IFC in the discharge port. If a 007-F5, the IFC part# would be 0010-025RP.

Dave H_2 · November 14

https://forum.heatinghelp.com/discussion/comment/1872302#Comment_1872302

And to add to that, in order to find the manufacturing date on the circ look at the electrical box near the wire knockout. It will have a date such as 0506 which would mean it was probably manufactured in Jan or Feb of 2006 (yes the circs get predated at manufacturing so that when you get them in your hands its close if not early for the jobsite)

EdTheHeaterMan · November 14

So your black pump may predate the 2006 date of manufacturer. if that is the case (because it was from "new old stock" when your system was assembled) You will need to add an external check. here is the one that taco makes for that purpose Taco Sweat Check. The Watts version Watts Flow Check is more expensive for the same thing. both have the opening screw on top for servicing or to allow gravity flow. You can also go cheap and not have that service screw on top with a generic check valve. 3/4" swing check

hot_rod · November 14

I would not use a swing check on a hydronic system.

1-They need a pressure differential to close and seal tightly, when a circ turns off pressure is the same on both sides of the check

2-Long travel length leads to water hammer

3- Most are not a bubble free seal, brass on brass in the bargain versions

4- swing checks need a full flow (gpm) to push the gate wide open, so must be sized based on the Cv number or they can chatter

The spring or weighted checks have that spring or weight to close them tightly and there opening or travel is a fraction of an inch.

Spring checks have a conical shaped valve, friendly to flow, low pressure drop.

One place a swing could be used is where you want the valve to open as hotter water pushes it open based on the buoyancy difference. Used for over-heat protection on wood boiler for example.

Hydronic Heat Zone heating when thermostat is off

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