No Hot Water to Some Zones

Bigbear

I hope you can help. My contractor installed a new boiler and reconfigured the piping for a primary/secondary heating system. The secondary pumps (5) feed radiant floor zones and a mixing valve provides 130 degree water. The primary boiler loop is set for 165 degrees. If any one zone calls for heat, no problem. But, if three zones are calling for heat, the first two zones will get hot but not the third. If 4 zones are calling for heat the first 3 zones get hot, but not the 4th. So, why is the last zone calling for heat, in the header, not getting hot? piping pictures attached. Thanks for your idea

s!!

EdTheHeaterMan

There is a pump missing.. Actually there is a flaw in the piping design. Let me look at this more closely.

EdTheHeaterMan

Looking at these check valves... this may be the problem.



If I'm not mistaken those valves are gravity operated check valves. Installing them on a vertical pipe may not allow them to properly close every time. So if there is no closed check valve on a zone that is not operating, then water in unused zones can flow backwards from the force of a pump on the operating zones. If the last zone on the manifold is off, then that inoperative zone will feed colder water into the zone that is operating closest to the zone that is off, as illustrated here.

EdTheHeaterMan

To test this theory, turn off a manual valve on the unused zones when you are experiencing the problem. With no alternate route for the water flow, this will prove that the lower temperature zone problem is a result of the open check valves on the unused zone(s). 2 pumps will have greater GPM that one pump. 3 pumps will have triple the flow in the common pipe. So it will be logical for all the water to come from more than one location.

I bet when all 5 zones are calling there is no problem.

hot_rod

Thats a lot of pumps on a small 3 cv mix valve
Any idea what the gpm requirement is?

Bigbear

OMG...it seems like zone 1 (left most) was culprit. I closed Z1 valve and any combo of other zones calling produced hot water in their zone! Amazing...thanks Ed!!  Regarding CV of the mixing valve, the originally installed was 3/4" and it was upside to 1". I'll keep an eye on it to determine if it should be full sized (1.25"). 

EdTheHeaterMan

Bigbear said:

OMG...it seems like zone 1 (left most) was culprit. I closed Z1 valve and any combo of other zones calling produced hot water in their zone! Amazing...thanks Ed!!  Regarding CV of the mixing valve, the originally installed was 3/4" and it was upside to 1". I'll keep an eye on it to determine if it should be full sized (1.25"). 

Those check valves may fail on the other zones at any time. The best fix is to have the installer put those valves on a horizontal pipe. Or add IFC kit inside the circulator pump(s) if that pump has one available.