Why does my heater shut off after 20 minutes?

A new heater shutting off after 20 minutes sounds like it could be a flow issue or an overheat protection kicking in. First thing I’d check is your water flow. Make sure the pump is running at the right speed and your filter is clean. If the flow is too low, the heater shuts off to protect itself. Also double-check your heater’s water pressure switch and temperature sensors. Sometimes new installs have minor wiring or plumbing issues that cause these shutdowns.
 
When I installed my new heater, I had the same problem and it turned out to be air trapped in the system. Bleeding the air out of the filter and heater solved it. Also check your thermostat settings. If the heater thinks the water reached the set temp, it will shut down, but 20 minutes is pretty fast. If flow and air checks don’t help, it’s worth calling the installer to check for a sensor or wiring problem.
 
I had a similar issue, and I like to think of my heater as a drama queen—it’s like it wants the perfect conditions before it agrees to work. Sometimes, I’ll even give it a little pep talk, like, ‘Come on, buddy, just heat up already!’ Anyone else try ‘convincing’ their heater to do its job?
 
Benjamin, when mine kept shutting off around the same time frame, it turned out to be something simple—low water flow. In my case, the filter was clean, but the pump speed wasn’t set high enough for the heater to operate optimally. Once I adjusted that, the problem stopped.

Another thing to look at is whether the heater is actually reaching the set temperature faster than you think. If the sensor is off, it might feel the water’s at the temp and cut out.

If neither of those checks out, I’d get the installer back for a quick look. A brand-new unit shouldn’t shut off that soon unless there’s a flow, wiring, or sensor issue.
 
Sounds like your heater is shutting down because it’s not sensing enough water flow or there’s trapped air in the system. Check that the pump is running at the right speed, the filter isn’t clogged, and bleed any air from the lines. If it still stops, a sensor or thermostat issue might be at play, so having the installer take a quick look is a good idea.
 
Mark Davis said:
A new heater shutting off after 20 minutes sounds like it could be a flow issue or an overheat protection kicking in. First thing I’d check is your water flow. Make sure the pump is running at the right speed and your filter is clean. If the flow is too low, the heater shuts off to protect itself. Also double-check your heater’s water pressure switch and temperature sensors. Sometimes new installs have minor wiring or plumbing issues that cause these shutdowns.
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Mine does every 15 minutes as a safety precaution.
 
Benjamin, I had the exact same thing with a new heater. For me, it turned out to be low water flow, the pump was running, but not fast enough to satisfy the heater’s safety sensors. Once I increased the pump speed and made sure the filter was fully clean, it stopped shutting off so quickly.

Also, check for any trapped air in the lines. Even a small air pocket can make the heater think there’s not enough water moving through, and it’ll shut down as a precaution. If those don’t fix it, it might be worth having the installer take a quick look, new units shouldn’t be turning off that fast under normal conditions.
 
Benjamin, that’s a pretty common hiccup with new heaters. Most often it’s a flow issue, either the pump speed isn’t high enough or there’s some trapped air in the system. Even a small air pocket can trick the heater into thinking there’s not enough water moving, so it shuts off as a safety measure.

Make sure your filter’s clean, bleed any air from the lines, and double-check the pump speed. If it’s still cutting out, it could be a sensor or thermostat thing, in which case a quick call to the installer is the easiest fix. A brand-new heater shouldn’t be shutting down that quickly under normal conditions.
 
Hey Benjamin, new heaters can be a bit finicky. One thing I noticed with mine was that even a tiny air bubble in the system would make it shut off after a short run. Also, some models have a “soft shutoff” feature if they think the water isn’t flowing quite right. I’d double-check the plumbing connections and make sure there’s nothing blocking flow. If all that looks good, having the installer run a quick diagnostic is the fastest way to pinpoint the issue.
 
Happened to me too, Benjamin, brand new heater and it kept shutting off like clockwork after about 15–20 minutes. In my case, it turned out to be a small air pocket in the line that kept tripping the flow sensor. Once I bled the air out of the filter and heater, it ran perfectly fine.

I’d also check that your pump speed is high enough and the filter’s spotless. Even slightly reduced flow can make the heater think there’s an issue and shut down to protect itself. If you’ve checked all that and it’s still happening, it might just be a sensor calibration issue, nothing major, but something the installer can usually sort out in one visit.
 
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