Back story. Started a job with a company a few weeks ago that installed 2 identical hydronics systems in new neighbouring town houses. I personally have very little hydronic experience but it's something I want to get in to.
They are both 4 loop radiant floor systems with a coil in a direct fired domestic water heater. Floor sizes and loop are the same, the tanks are the same model, components are the same.
Working system the tank has 160F outlet temp. The radiant return is 78F, supply is about 130F for a 52F temp rise. Using a mixing valve we have tempered it down to 105F to supply the floors with a flow rate of .5GPM.
Neighbouring unit has a tank outlet of 160F, radiant return of 78F but supply of 95F for a 17F temp rise with .5gpm. Not hot enough for floors.
So here's where the issues arise........
Mixing valve tightened all the way in, forces flow through the tank and gives good temp rise to 130F same as the other system but way to hot to go to concrete floors also cuts flow to manifold to 0gpm.
As soon as you open mixing valve, flow increases to normal, temp rises until all the 'backed up' hot water flows through and then drops to original low temp.
Here's what we've tried:
Replaced mixing valve.....same thing happens.
T to return and through mixing valve was a few inches apart so we moved it so it's a couple of feet apart thinking maybe it was pulling cold water through valve instead of through the tank. Same issues. (other system the T is about 6 inches from mixing valve and work fine).
The pump is working and is the same on both systems and at same speed.
We checked flow through the tank in case it's a blocked heatX but it's fine.
So any ideas or anymore info you'd need to know?
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