JLN
New Member
I have a Navien NCB-240E combi located on the third floor supplying DHW to the house and infloor hydronic to the first floor. It feeds a 3-loop Wirsbo manifold on the first floor (two loops on one thermostat and one on another). A Grundfos Alpha 15-55F (maybe 5-6 years old) is on the return side and also on the first floor. I did just read, I think on this forum, a comment that it would be better to have the pump on the supply side, but the system has been in place about 30 years and working flawlessly except for replacing the pump and the Navien a couple of years ago.
If you don't want to read further - the pump now runs only at 1 GPM at max amps, though I'm pretty sure it used to run at 3 GPM with all zones demanding heat? Can it have a "partial" internal failure or am I having some other problem like air?
The long story: I recently had a plumber replace the end gaskets on the Wirsbo manifold because one was allowing a slow drip that could not be stopped by tightening and my back would not allow me to get at it myself. He restarted the system and all seemed well but I noticed the following day (about 18 hours elapsed) that the hydronic system was not heating the floor as usual. The pump was running on Auto, where it has always been set. I checked the tubing near the supply and return manifolds and could detect no heat and the pump sounded a bit noisier than usual. The pipe within about a foot above and below the pump was warm. I figured the pump was cavitating water and that there was an airblock somewhere. I tried various things unsuccessfully to bleed air from the system. I set the pump to max amps and heard some gurgling and the pump got quieter, more normal sounding. After a while I could feel warmth in the tubing of each loop but supply side registered only about 90 degrees each and the return was approximately ambient. I'm pretty sure each supply side used to get to about 110-120 and in the 90s on the return side (using an infrared thermometer), even on very cold days. I checked each loop by manually opening and closing the actuators and each loop responded by getting slightly warmer on the return side. The pump shows only 0 GPM on Auto and the low constant settings. It shows constant 1 GPM only at highest amp setting no matter how many loops are open. When changing setting it may briefly flash 2 GPM but immediately goes back to 1 GPM. I never paid much attention but I'm almost certain that it used to run at 3 GPM when all three zones were demanding heat. Plumber said the problem is air and to leave the pump running at max amps. It's been doing that for a week with no change. The Navien runs in its low (standby mode?) the entire time but goes into high gear when it needs to supply domestic water. Turning radiant demand on and off has no effect. I'm quite certain that the frequency of the Navien going into high gear used to be in proportion to how cold the house is (=frequency of demand). There is a brand new expansion tank precharged to 15 PSI and a Webstone Air Eliminator at the Navien. Opening the bleed valve on the air eliminator occasionally releases a tiny puff of air, as does the air vent in the Navien. I've also tried venting air at the highest pressure relief on the Navien. That generated some air once but now only water comes out. If the problem is micro bubbles, I don't see why that would prevent the Grundfos from increasing its delivery. Unfortunately there are no valves on the radiant loops so I can't try flushing them directly. Big bubbles in each loop seems to be the only option left if the Grundfos hasn't gone bad. I would be grateful for advice.
If you don't want to read further - the pump now runs only at 1 GPM at max amps, though I'm pretty sure it used to run at 3 GPM with all zones demanding heat? Can it have a "partial" internal failure or am I having some other problem like air?
The long story: I recently had a plumber replace the end gaskets on the Wirsbo manifold because one was allowing a slow drip that could not be stopped by tightening and my back would not allow me to get at it myself. He restarted the system and all seemed well but I noticed the following day (about 18 hours elapsed) that the hydronic system was not heating the floor as usual. The pump was running on Auto, where it has always been set. I checked the tubing near the supply and return manifolds and could detect no heat and the pump sounded a bit noisier than usual. The pipe within about a foot above and below the pump was warm. I figured the pump was cavitating water and that there was an airblock somewhere. I tried various things unsuccessfully to bleed air from the system. I set the pump to max amps and heard some gurgling and the pump got quieter, more normal sounding. After a while I could feel warmth in the tubing of each loop but supply side registered only about 90 degrees each and the return was approximately ambient. I'm pretty sure each supply side used to get to about 110-120 and in the 90s on the return side (using an infrared thermometer), even on very cold days. I checked each loop by manually opening and closing the actuators and each loop responded by getting slightly warmer on the return side. The pump shows only 0 GPM on Auto and the low constant settings. It shows constant 1 GPM only at highest amp setting no matter how many loops are open. When changing setting it may briefly flash 2 GPM but immediately goes back to 1 GPM. I never paid much attention but I'm almost certain that it used to run at 3 GPM when all three zones were demanding heat. Plumber said the problem is air and to leave the pump running at max amps. It's been doing that for a week with no change. The Navien runs in its low (standby mode?) the entire time but goes into high gear when it needs to supply domestic water. Turning radiant demand on and off has no effect. I'm quite certain that the frequency of the Navien going into high gear used to be in proportion to how cold the house is (=frequency of demand). There is a brand new expansion tank precharged to 15 PSI and a Webstone Air Eliminator at the Navien. Opening the bleed valve on the air eliminator occasionally releases a tiny puff of air, as does the air vent in the Navien. I've also tried venting air at the highest pressure relief on the Navien. That generated some air once but now only water comes out. If the problem is micro bubbles, I don't see why that would prevent the Grundfos from increasing its delivery. Unfortunately there are no valves on the radiant loops so I can't try flushing them directly. Big bubbles in each loop seems to be the only option left if the Grundfos hasn't gone bad. I would be grateful for advice.
