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Tankless water heater issues
Posted on 8/27/26 at 7:13 am
Posted on 8/27/26 at 7:13 am
I have a state tankless water heater (gas) that will provide hot water for several minutes, then cool off in the middle of a shower. At times it will also only get lukewarm, as opposed to get hot, and at times it will not get hot at all. Does anyone have experience with this and have any idea how to troubleshoot this? This behavior also goes on with the sink faucets as well, so it is not a just a shower issue. The water heater is about 6 years old.
This post was edited on 8/27/26 at 7:17 am
Posted on 8/27/26 at 9:07 am to tigerrage08
Sometimes old school is the best.
Posted on 8/27/26 at 9:49 am to tigerrage08
Look up "Cold Water Sandwich" and see if that is it.
Posted on 8/27/26 at 12:16 pm to tigerrage08
Are you on a well? We had this issue and had to turn up pressure to get enough flow. On a particular low flow shower we had to run the hot water in the sink during a shower to keep hot water.
Posted on 8/27/26 at 12:28 pm to way_south
No well, city water.
Posted on 8/27/26 at 12:53 pm to tigerrage08
I was told they had to be de-scaled yearly.. that factored in to not transitioning to that style when I replaced mine.
Posted on 8/27/26 at 1:06 pm to Shepherd
A lot of people don't but you're also supposed to flush the regular tank type as well.
Posted on 8/27/26 at 3:19 pm to tigerrage08
Make sure you have the right gas line size feeding it.
Posted on 8/27/26 at 7:14 pm to tigerrage08
Actually yes, yes I do. I have a 3 year old state GTS510 outdoor unit. Had a similar problem a couple months ago. Mine would vent really loud and couldn’t handle low flow (slightly warm showers) without losing flame, and would randomly shut off in the middle of a bath or shower.
You have to call customer support and they will transfer you to technical support and open a case. If it’s within warranty they will help line that up. If not, they will troubleshoot it with you to determine what the issue could be and send you whatever parts to change.
I called and she walked through troubleshooting with me. Sent me a text with a link to a video call app where she used an on screen arrow to point to things she needed me to check. It was pretty legit. She was perplexed by what it could be so she put me on hold to consult her team. They came back with low flow valve on the valve and manifold assembly, so they sent me one.
That ended up being exactly right. The low flow valve wasn’t working properly, so anytime flow would be low enough to only engage the low flow valve it would lose flame. I changed it and has worked perfectly ever since.
You have to call customer support and they will transfer you to technical support and open a case. If it’s within warranty they will help line that up. If not, they will troubleshoot it with you to determine what the issue could be and send you whatever parts to change.
I called and she walked through troubleshooting with me. Sent me a text with a link to a video call app where she used an on screen arrow to point to things she needed me to check. It was pretty legit. She was perplexed by what it could be so she put me on hold to consult her team. They came back with low flow valve on the valve and manifold assembly, so they sent me one.
That ended up being exactly right. The low flow valve wasn’t working properly, so anytime flow would be low enough to only engage the low flow valve it would lose flame. I changed it and has worked perfectly ever since.
Posted on 8/27/26 at 8:10 pm to tigerrage08
I had this same issue. After doing some research, my shower head put out more than 2 GPM. The on demand hot water system couldn't keep up with that flowrate. I replaced the shower head to a 1.8 GPM (recommendations are for a GPM < 2 GPM). This solved my problem and I haven't had any issues since. I hope this helps and solves your problem as well.
Posted on 8/27/26 at 8:34 pm to tigerrage08
Had a tankless fail after 3 years. Im all tank now and its glorious.
Posted on 8/27/26 at 9:09 pm to Scarface
how small of a a water heater you buy that it can't feed 2 gallons per minute. they even make such an animal
Posted on 8/27/26 at 10:02 pm to Scarface
quote:
I had this same issue. After doing some research, my shower head put out more than 2 GPM. The on demand hot water system couldn't keep up with that flowrate. I replaced the shower head to a 1.8 GPM (recommendations are for a GPM < 2 GPM).
I have an 11.1 GPM tankless, and I have to turn every faucet on in the house, along with all three tubs and a shower, and then, and only then, it can't keep up to produce enough hot water for all faucets, tubs, and shower.
Posted on 8/28/26 at 12:21 pm to Will Cover
i had this problem only in my shower. took the restrictor out the shower head and never had a problem since
Posted on 8/28/26 at 10:13 pm to tigerrage08
Had the same problem. You need to descale your tank. ( super easy ). Then change the check valve ( super easy and $4 for the new part)
YouTube told me everything when the plumber couldn’t figure it out
YouTube told me everything when the plumber couldn’t figure it out
Posted on 8/29/26 at 12:04 am to Maillard
It was already installed in the house when I bought it. The master shower was the only one that would go cold, never get hot, or work fine sometimes. All other faucets worked great. When I changed the shower head, it corrected the issue. I know it sounds strange, but that's what fixed it.
Posted on 8/29/26 at 9:47 am to tigerrage08
you’ve gotten good advice it’s almost always a flow issue. The other thing you can try is to turn the temp down some
Posted on 8/31/26 at 11:20 am to cgrand
I had the opposite problem of most here I believe. I did not have enough flow so I took the flow restrictor out of the shower head. I still have the issue of the water is running in another part of the house on my old hot water heater that feeds the rest of the house so there is not enough flow through the tankless in my master. Not really sure how to fix that if anyone has any ideas.
Posted on 8/31/26 at 2:16 pm to tigerrage08
I have a pair of Rinnai Tankless and it is the best hot water situation I've ever had. I descale both of mine in April and October and they have run great for me. I would never want to go back.
Do you have water pressure issues? They do have to have enough flow to click on.
Do you have water pressure issues? They do have to have enough flow to click on.
Posted on 8/31/26 at 4:35 pm to tigerrage08
Error codes?
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