Trouble with Navien tankless with recirc and Grohe shower

Users who are viewing this thread

ndubs02

New Member
Messages
2
Reaction score
0
Points
1
Location
California
Hi everyone,

First time posting here, and I appreciate any responses in advance. I'm come here lots of times looking for troubleshooting tips and have usually found what I needed without posting. But my current situation has got me stumped.

I live in a house that was built 7 years ago with a Navien NPE 240A tankless water heater and a recirc line, water heater is set at 130F. For the most part - the water heater seems to work well and the recirc lines do provide warm water quickly. However, in our second bathroom (which the kids use, not me), the kids starting complaining that the water doesn't heat up for a long time. This bathroom has a Grohe pressure balancing shower valve. At first I didn't believe them because I would try it and everything seemed OK, but then I was able to observe the issue myself, and have been able to get it to happen multiple times since then (not every time, but most times). This fixture is the furthest or second furthest in the house from the water heater - two floors above, and about 30ft away.

What happens is that when you turn the shower on full hot, the water starts warm (about 100F). then after about 2 minutes on full flow, it starts to cool down, I've used a thermometer and it gets down to 80-85F. Then after about 5-7 total minutes it starts to warm up and gets back to 110-115 after nearly 10 minutes. If I contrast this with the shower that I use, when you flip it on all the way hot, it starts at about 100F, then maybe drops just a touch for 10-15 seconds, then back to 105-110 within a minute and settles out at 120 or so when you need to turn it down a touch for comfort.

For a while, I suspected, something was going on with the water heater, but then this weekend I had my daughter assist me and I was able to watch the info screen on the water heater while she turned on the shower and watched the thermometer. At the info screen, I could see the water heater turn on, measuring 1.4gpm output, 58F input and 128-129F output. I didn't see any issues where the heater cycled off or anything, it seemed perfectly stable sitting at 1.4GPM and 128F out.

So now I am maybe suspecting either that the pressure balancing valve at the shower might be malfunctioning in some strange way - or I have wondered if the original install was done incorrectly, maybe the water is coming backwards from the cold supply the wrong way through the return line? (although then I don't know why the water heater would measure 1.4GPM output.

Any ideas here about what are the likely culrits and how I can debug further? I have thought perhaps I should just change the shower cartridge (I can order that and probably can change it myself), but not sure if there is anything else obvious that I could try to narrow down the offending system.

Thanks!
 

ndubs02

New Member
Messages
2
Reaction score
0
Points
1
Location
California
Your recirc line is it always hot?
I’m not sure how I would measure it to make sure, but as far as I can tell the Navien heater circulates the line ever so often to heat it up. I think put a video camera on that years ago and saw that indeed that every now and then it turns on the pump and heater. The other way I would say that I can tell is that the other fixtures in the house get warm water within 10 or so seconds. We do not have a hot button and I do not believe the heater is set up with any schedule or anything.
 

John Gayewski

In the Trades
Messages
4,832
Reaction score
1,556
Points
113
Location
Iowa
You should be able to put your hand on the recirc line to see if it's warm.

At this point I would suspect the shower valve if everything else acts normally.
 

Breplum

Licensed plumbing contractor
Messages
2,405
Reaction score
1,025
Points
113
Location
San Francisco Bay Area
The first thing to do is replace the internal check valve. They are quite notorious for becoming stuck open because the black o-ring breaks down. This results in hot water drift...but sometimes more pronounced at different fixtures.
Watch a youtube video on how to change the check valve. very easy. the check valves are typically under $5 from a Navien distributor/plumbing wholesaler shop that carries them...or maybe very overpriced on line and shipping adds a ton.
Part number is 30008359A or 60A
 
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