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why am I having heating issues with respects to radiant zone not working, but once was?

The job was a complete gut and remodel. so we used the open floor below to provide radiant heat to a master bedroom and a master bath.
method of piping was 1/2" pex, stapled to underside of sub floor then heat reflective shield installed over then insulated between floor joists. average spacing is 7 inches between piping.
master bedroom floor is hardwood and master bath is marble with mud job.
master bath about 127 sq ft and master bedroom 225 sq ft.
hot water source is a mini boiler electric (boiler is manufactured by "electro industries").
2 zone set up. Boiler supplies water to a taco x pump block (XPB).
Both zone valves are working.
Thermos stats correctly trigger the zones to open.
returns are hot (not as hot as supplies).
The master bedroom works great even in the serious cold the northeast has been experiencing. but the bathroom zone that had once worked is not getting hot. both the bedroom and the bath are piped the same and the bath is actually a shorter run.
At one point we were having issues with the bedroom not getting enough heat and the bath continually heating great.
While looking at why the plumber noticed that the wrong valve was used and that valve would constrict water flow. Since the valve was replaced with a full port valve the bedroom heat has been on point but the bathroom heat has disappeared.
system has been bled and there are air separators as well. Zone valves were taken apart to look for possible blockages.

My plumber has no answer, but is game for a solution and is doing his due diligence. Both of us feel it might have something to do with the taco block. any ideas or observances.

I appreciate any guidance that can be contributed to this matter.
Thank You


  • Jamie Hall
    Jamie Hall Member Posts: 22,934
    Does this happen when only one of the two zones is calling? What happens if you turn off the heat to one zone? Does the other get warm? (I'm assuming you have only one circulator pump). If so, the resistance to flow in the zone which doesn't get hot when both are calling is significantly greater than in the other. Water is lazy... find the resistance to flow.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Snowmelt
    Snowmelt Member Posts: 1,405
    If it worked befor I think you have air in line, do you have near boiler piping?