Grundfos Alpha 15-55f stuck in 1 GPM

Users who are viewing this thread

JLN

New Member
Messages
4
Reaction score
0
Points
1
Location
Washington, DC
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.
 

zebu

New Member
Messages
3
Reaction score
0
Points
1
Location
Westchester
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.
Verify the pump water flow direction.
 

John Gayewski

In the Trades
Messages
4,548
Reaction score
1,449
Points
113
Location
Iowa
Still sounds like air. If your getting air then it's air.

Can you shut the balancing valve on each loop individually and try to bleed them one at a time? Your might need to shut everything off and use the fill valve to bleed the air.
 

JLN

New Member
Messages
4
Reaction score
0
Points
1
Location
Washington, DC
Still sounds like air. If your getting air then it's air.

Can you shut the balancing valve on each loop individually and try to bleed them one at a time? Your might need to shut everything off and use the fill valve to bleed the air.
Thanks. Unfortunately, no balancing valves and no individual shut-offs, except keeping actuators shut. The Navien and manifold are the high points in the system. I thought the pressure relief valve at the Navien high point might be a place to bleed air but I only get water. I'm not hearing a puff of air escape from either the eliminator valve or Navien's own air valve when I open them. The Navien slowly drops pressure about 1 psi every 2-3 days. I have the make-up water shut and fill it manually when the air error shows. I'm not seeing any evidence of a water leak (but that's how I did find the drip at the manifold). The entire radiant infloor heat is above a drywall ceiling that should eventually show if there were a leak:-/ I think. Is it reasonable to assume (or hope) that this is because the system is releasing air? When I shut down the loops one by one and check temp in tubing, there is heated water going through each, just at a very slow rate.
 

JLN

New Member
Messages
4
Reaction score
0
Points
1
Location
Washington, DC
Sorry for confusion. I said I got a tiny puff of air when I opened the air vents a couple of times in the first two days after manifold was reconnected. Each puff was less than a fraction of a second and barely audible - less than you get when first opening a sealed jar. Not a hint in last 10 days. I also got a few seconds of gurgling and what I assumed was air when I opened the pressure relief valve at top of Navien while it was restarting after the manifold fix. Since then no gurgle and I get only water. Just checked pex tubes again. All three zones are getting warm water but only luke warm. DHW gets plenty hot.
 

John Gayewski

In the Trades
Messages
4,548
Reaction score
1,449
Points
113
Location
Iowa
If all of your valves are open and your pump is only pumping what seems to be slowly it's probably your pump.

Can you take a picture of the piping setup?
 

JLN

New Member
Messages
4
Reaction score
0
Points
1
Location
Washington, DC
Ha, no offense, but unlike the pictures I see of systems nicely laid out along a basement wall, I don't expect anyone to be able to get anything from pictures of my setup. It's tucked into a 3rd floor closet and in addition to the Navien integrates a heat pump and rooftop glycol thermal loop with a dual heat-exchanger solar hot water tank (the heat pump's air handler and the hot water tank live in a utility closet next to this one). It took me only a few hours to trace pipes and figure out which ones go where, never mind the electronics. That said, I'm not worried about the structure of the system. It has been operating fine for about 12 years, with the Navien replaced 3 years ago, and the expansion tank a few weeks ago (turns out it didn't need to be replaced), and leaking gaskets on the 1st floor manifold for the infloor radiant heat (water is tempered by solar thermal). When the pump was working properly, this 1st floor radiant actually suffices to heat the 3-story house most of the winter. The heat pump gets called into action only when outside is below 20F for more than 2 days in a row.

To my mind opening the manifold to replace the gaskets led to the Grundfos now behaving in suboptimal mode - that is, it no longer demands more than 1 gpm hot water from the Navien.

I have a bunch of other alligators nipping at my butt right now but I will take the pump off as soon as I can to see if something got loosened and now is impeding flow.
 

Attachments

  • NavienSetup.jpg
    NavienSetup.jpg
    76.9 KB · Views: 48
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks