Hello,

We are in the finishing stage of a new home construction with an Uponor closed-loop in-floor radiant system powered by a Nordic ground-source heat pump.  The system has 4 zones with the basement zone in 4-inch concrete slabe over 2" EPS and poly and the upper zones in 1.5" maxxon therma floor over plywood sub-floor.

System has been running smoothly for a few months now, but suddenly this past Friday I noticed a system pressure drop and obvious signs of air in the system (farting noises from the zone circulator pumps).  Prior to this the system pressure was running between 30-40 psi, now I'm seeing pressures from 0 - 18 psi depending on how many zones are calling for heat.

The only other this I had this problem was 2 months ago when my drywall contractor mistook the basement manifold valve for a domestic hose bib and discharged water from the system.  In that particular the case the pressure dropped to zero and never recovered wheres in the current situation I've still got positive pressure, just very slow (and perhaps decreasing).  I don't think in this case it was cause by someone mistakenly using one of the valves for water since we capped them all after the last incident.

I'm hoping perhaps there is something wrong with the expansion tank, but what are the chances that a leak has developed after running smooth for a few months.

I've done a thorough investigation (as much as possible with ceilings and walls closed up) and can find no evidence of water.  If there were a slow leak in either the basement or upper loops, would there be obvious signs?

Thanks for any input you can provide.

I'll be speaking with my HVAC guy tomorrow but if anyone can provide some thoughts it would be much appreciated.

Assuming you loose pressure you probably have a leak, then the next steep is the old process of elimination. First isolating manifolds, looking manifold by manifold for a pressure drop. This takes time, perhaps 24 hours on each manifold. Then once you have the manifold that is loosing pressure you go to a circuit by circuit review, Ultimately you will confirm what loop has the leek.
Could also be air in the system, Perhaps you do not have a quality air eliminator. And last with the right air eliminator there also needs to be an auto fill. Have your contractor provide an explanation of the system, and most important how to isolate manifold and circuit by circuit in the unlikely event of a future leak,
Dan

My HVAC contractor is certain that someone drained water from the system.  Based on the pressure drop it lost about a gallon of water and it happened over a short period of time.  I would think a gallon of water leaking over a 24 hour period would be noticeable somewhere.  I've added water back to the system to re-pressurize, we'll see if it drops again.

30 to 40 psi you say?

Yep, depending in the temperature of the water and how many of the loop pumps were running at any given time...  also depending if the heat pump circulator pump was running.

Have you system scanned using infrared thermographic technology

Why is the system operated at 40psi?

good question, any boiler I have worked with has a Pressiure relief valve @ 30psi unless intentionally changed to a 50.
Further if you are holding pressure for now you are probably fine and the system was scrubbing air and settling in.
Flip on the heat and relax, you have a boiler room!
It is a good time to have a glass of wine and praise yourself for the right choice to go hydronic in your new home!
May I recommend a Washington red?
Dan

Not sure really, this is my first experience with in-floor.  Might have something to do with the Geothermal heat pump?  I think the installer will be setting it to 30psi once it's all balanced.  There's still 2 more loops to connect for a hydronic air handler and hydronic radiator.

Thanks Dan.

The heat is on, but no time to relax yet.  Cabinets are going in this week and we'll be moving in end of this month.

But I will take the suggestion for a Washington red once we're in!