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Message
Tankless Water Heater Issue
Posted on 9/9/25 at 9:46 am
Posted on 9/9/25 at 9:46 am
I've been having a gas tankless water heater for a couple years now. My 50 gallon electric busted, and we had it replaced with this one.
It's a State (Takagi) GTS 510 U 199,000 BTU Outdoor unit.
It's hard enough to get the plumber to come back out and look into this, between my schedule and his, so if this is an easy fix I'd like to see if I can take care of it myself.
Confirmed fuel supply is more than adequate, water pressure is good, etc..
The issue is it constantly cuts off and reignites when using it. Over time I've narrowed it down to this: It has trouble adjusting to or accommodating changes in flow. If there are multiple fixtures running hot water at the same time, cut one of those fixtures off and it shuts off and vents, then re-recognizes the flow of the other fixture that never stopped, reignites, and runs. Sometimes it never reignites, so you have to turn off your fixture and wait a few seconds, then turn it back on, and it'll recognize the flow and ignite. Sometimes it goes into a constant cycling loop, shut off, vent, reignite, shut off, vent, reignite...
Once when this happened (two fixtures running, turn one off and it shut off and didn't reignite) I went outside to check the display, and it was showing the flow gpm, but was blinking in standby mode.
The error message on the display reads Loss of Flame, but I think that's the symptom rather than the root cause.
I've contacted State and they told me I need to call them during business hours to troubleshoot with them. It's hard to find the time to break free during business hours to do that.
From what I'm gathering it could potentially be the flow sensor. I plan to try and open it up to inspect the flow sensor this weekend.
Anyone have a similar issue or have any ideas?
It's a State (Takagi) GTS 510 U 199,000 BTU Outdoor unit.
It's hard enough to get the plumber to come back out and look into this, between my schedule and his, so if this is an easy fix I'd like to see if I can take care of it myself.
Confirmed fuel supply is more than adequate, water pressure is good, etc..
The issue is it constantly cuts off and reignites when using it. Over time I've narrowed it down to this: It has trouble adjusting to or accommodating changes in flow. If there are multiple fixtures running hot water at the same time, cut one of those fixtures off and it shuts off and vents, then re-recognizes the flow of the other fixture that never stopped, reignites, and runs. Sometimes it never reignites, so you have to turn off your fixture and wait a few seconds, then turn it back on, and it'll recognize the flow and ignite. Sometimes it goes into a constant cycling loop, shut off, vent, reignite, shut off, vent, reignite...
Once when this happened (two fixtures running, turn one off and it shut off and didn't reignite) I went outside to check the display, and it was showing the flow gpm, but was blinking in standby mode.
The error message on the display reads Loss of Flame, but I think that's the symptom rather than the root cause.
I've contacted State and they told me I need to call them during business hours to troubleshoot with them. It's hard to find the time to break free during business hours to do that.
From what I'm gathering it could potentially be the flow sensor. I plan to try and open it up to inspect the flow sensor this weekend.
Anyone have a similar issue or have any ideas?
This post was edited on 9/9/25 at 9:48 am
8
Posted on 9/9/25 at 9:47 am to TheBoo
This is a Wendy’s but…
I love mine. Never run out of hot water, no issues so far.
I love mine. Never run out of hot water, no issues so far.
Posted on 9/9/25 at 9:56 am to TheBoo
quote:
Tankless Water Heater Issue
Tossed your symptoms into CHATgpt. Since it's several years old and I assume the problem just started, I weeded out some responses. Below is your most likely issues:
Clean Flow Sensor
Shut water off, pull the inlet filter screen, and flush debris.
If comfortable, inspect the flow sensor (small turbine inside). Mineral buildup makes it stick or spin intermittently.
Descale the Unit
If not done in the past 12–18 months, run a vinegar or tankless descaling solution flush through the unit.
Scale can cause erratic temp spikes ? shutdowns.
Inspect Flame Rod & Burner
Flame sensor rod can carbon up or corrode. A light emery cloth cleaning often helps with flame recognition.
Posted on 9/9/25 at 10:14 am to RaginRampage
Thanks. I descaled it a few months ago. It's only 2 years old.
Posted on 9/9/25 at 10:27 am to TheBoo
Mine if i set the temperature to hot on the heater it will work for a bit then flash an error code. Mine goes up to 165 degrees, it seems the spot to set it is 155 and it wont give me any problems
what temp is yours set at?
what temp is yours set at?
Posted on 9/9/25 at 10:32 am to TheBoo
Is there any kind of filter in the heater? We had one of these on one of our buildings several years ago and this would happen when the filter needed replaced/cleaned.
Posted on 9/9/25 at 10:33 am to TheBoo
quote:
I've contacted State and they told me I need to call them during business hours to troubleshoot with them. It's hard to find the time to break free during business hours to do that.
You need to do this, especially if its under warranty.
When I did plumbing work years ago in high school, we had to walk thru the troubleshooting steps over the phone in order for them to warranty any replacement part.
Sounds like a flow sensor but with the issues you described, it wouldn't surprise me if it ended up being a bad control board either. We changed many of those across all brands.... granted that was years ago when they were somewhat new to market.
Posted on 9/9/25 at 12:44 pm to southern686
hank y'all for the feedback. I've found that if I bump the temperature down it gets slightly better, since demand for hot water increases.
The filter was completely clean when I checked again this weekend.
Thanks. I'll figure out when I can take a day and call them.
The filter was completely clean when I checked again this weekend.
quote:
You need to do this, especially if its under warranty.
When I did plumbing work years ago in high school, we had to walk thru the troubleshooting steps over the phone in order for them to warranty any replacement part.
Sounds like a flow sensor but with the issues you described, it wouldn't surprise me if it ended up being a bad control board either. We changed many of those across all brands.... granted that was years ago when they were somewhat new to market.
Thanks. I'll figure out when I can take a day and call them.
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