Oven temperature keeps jumping up and down (temperature fluctuations)

You set the oven to 350°F. Sometimes it shoots up to 410°F and scorches food. Then five minutes later it drops to 290°F and nothing finishes on time. The cooks start blaming the recipe, but it’s not the recipe. It’s temperature control.

When a commercial oven can’t hold a steady temperature — big swings high, big drops low — that’s a control problem. As a tech, I look at three things right away:

Are the heating components being switched on/off correctly? (relays, contactors)
Is the oven reading the temperature correctly? (temperature probe/sensor)
Is the control brain actually tuned to control heat smoothly? (PID or thermostat calibration)

Let’s go through what’s really happening, what’s normal vs not normal, and how we fix it.

The complaint I hear in kitchens

It usually sounds like this:

“Every batch is different.”
“We’re burning trays in the morning and undercooking at lunch.”
“Display says 350°F but I’m seeing 380°F, then 300°F.”
“We can’t run consistent product anymore — prep keeps coming back.”

This is not just “old oven behavior.” This is an oven that is no longer regulating heat like it should. And it’s fixable.

Problem #1: Sticking or failing relays

Most commercial ovens don’t just send power straight to heating elements all the time. They pulse heat on and off using relays or contactors.

When the oven calls for heat → relay closes → elements or burner fire.
When it’s hot enough → relay opens → heat cuts.

If that relay is worn, pitted, arcing, or sticking, you get chaos.

What that looks like in real life:

Temperature shoots way above set point because the relay stuck “on” too long.
Or: temp drops too far because the relay didn’t pull in when it should have.
You get giant overshoot, then the unit overcorrects and crashes low.

On gas equipment, a similar thing happens if the gas valve or control is slow or chattering. It’s the same story: the oven is not being allowed to “feather” the heat gently — it’s either blasting or starving.

What I do:

I watch the control call for heat and I watch (or meter) the relay/contactor actually switching.
If it’s lagging, buzzing, welded, or intermittent, we replace it. You can’t “clean it and hope” for long — if the contacts are cooked, that relay is done.

Once a bad relay is replaced, you usually see way tighter swings immediately.

Problem #2: Bad or drifting temperature probe

The oven can only control what it can measure. If the probe (temp sensor) is lying, the controller will constantly chase the wrong number.

Here’s how that goes wrong:

The sensor reads low → oven thinks it’s cooler than it is → it keeps adding heat → you overshoot by 30–60°F.
The sensor reads high → oven thinks it’s already hot → it cuts heat early → temp freefalls and your product never finishes.

Another classic: loose probe or damaged wiring causes “jumping.” So the controller thinks the temperature just crashed 40°F in one second — it panics, slams heat on full blast, then overshoots. That’s how you end up with swings.

What kills probes?

Grease and carbon buildup baking onto the sensor.
Physical abuse (pans slamming into the back wall).
Age drift — sensor just stops reporting accurately.

What I do:

I don’t trust the display. I bring my own calibrated thermometer and log what’s actually happening in the cavity.
I compare “real cavity temperature” vs “what the board thinks.”
If there’s a gap, we either recalibrate (if the control allows an offset) or replace the probe.

If your screen says 350°F but a real meter is showing 395°F and then 320°F five minutes later, that probe is lying or the wiring is unstable. That has to be fixed before you will ever get stable temperature.

Problem #3: PID / thermostat tuning is out of control

Commercial ovens use either:

a mechanical thermostat (older units), or
an electronic controller that behaves like a PID (Proportional / Integral / Derivative loop) — basically, a smarter thermostat.

Plain English version:

The controller is supposed to “learn” how hard to fire the heat and when to back off so you don’t overshoot.
If that tuning is off, the oven behaves like a bad driver: gas pedal all the way down, then slam brakes, then gas again.

That gives you the “rollercoaster” temperature graph:

360°F → 390°F → 320°F → 375°F → 305°F…
Food quality becomes inconsistent from rack to rack, batch to batch.

Why does tuning go bad?

Control board was replaced and never dialed in.
Unit was moved or vented differently, so it now heats faster/slower than before.
Someone tried to “turn it up a little” or bypass safeties, and now it’s just hunting.

What I do:

On digital/PID-style ovens: I stabilize it. That means adjusting the control response so it stops overshooting and undershooting so aggressively.
On older thermostat units: I test the thermostat for calibration and hysteresis. If the stat has a huge swing, we either recalibrate it (if possible) or replace it.

Once the control is tuned right, the oven ramps smoothly to set temp and just gently maintains instead of yo-yoing 50°F up and down.

Other contributors we check (still important)

These aren’t always the main cause, but they make fluctuations worse:

Door seal leaks (gasket damage).
If you’re dumping heat out the door constantly, the oven keeps calling for more heat. That constant “full blast / cool down / full blast / cool down” cycle exaggerates swings.
Fan / airflow problems.
A failing circulation fan or blocked airflow can create hot spots and cold spots. The probe might be sitting in a hot pocket of air while the rest of the cavity is actually cooler — so the controller thinks “we’re good,” then the rest of the oven tanks in temp.
Overloading / blocking vents with foil or pans.
If staff blocks air movement to “hold more product,” you’ll get unstable temperatures. That’s not an equipment failure, that’s just choking the oven.

I still call it out to the kitchen because even if I tune everything perfectly, if airflow is suffocated the oven will behave unstable in actual service.

Why this matters to you (beyond being annoying)

Inconsistent product. One tray comes out burned, next tray pale. Your brand takes the hit, not the oven.
Food safety. If the oven drops too low mid-cycle, you might not hit safe internal temps on proteins.
Ticket time. Kitchen timing goes off. You start holding food longer “to finish it,” and that kills quality.
Energy waste. A unit that’s constantly slamming to max heat, then idling, then slamming again is burning money.

A steady oven isn’t a luxury. It’s consistency, safety, and cost control.

What we actually do on a service call

When you call us for “temperature all over the place,” here’s the workflow:

Watch the swings under load.
I run the oven, log the real internal temperature, and compare it to what the display/controller says.
Check and test relays/contactors.
If the heat output is sticking or lagging, that relay is coming out.
Verify the temp probe.
If the sensor is drifting or jumping, we replace it or recalibrate the readout so it matches reality.
Tune the control (PID/thermostat).
I stabilize how aggressively the unit applies heat so it stops “yo-yo heating.”
Check seal and airflow.
I make sure we’re not chasing a basic gasket leak or a dying fan.

After that, the oven should heat normally, hold within a tight window, and stop cooking like a mood swing.

FAQ: Temperature fluctuations in a commercial oven

Why does my oven overshoot set temp by 40–50°F and then drop too low?
Usually it’s a control issue: sticking relays, a bad temperature probe feeding bad data, or aggressive/untuned PID settings that are slamming heat on and off instead of modulating.

Why is one batch perfect and the next batch undercooked?
Because you’re not actually cooking at a stable temperature. The display might say 350°F the whole time, but internally you’re bouncing between “way too hot” and “too cold.”

Can this be fixed without replacing the whole oven?
Most of the time, yes. We stabilize relays, replace/clean/verify the probe, and tune the control logic. Full replacement is usually not step one.

Is it safe to keep using it like this?
From a food safety and consistency standpoint: not really. You’re guessing. And in a commercial kitchen, guessing is how you get refunds and bad reviews.

What do you adjust when you’re done?
We leave you with an oven that ramps predictably to the set temperature, and then holds that temp with small controlled corrections — not 70°F swings.

Final word from a tech

Big temperature swings are not “just how this oven cooks now.” They’re almost always electrical control issues: relays sticking, sensors lying, or tuning that’s way off. When we service it, we stabilize the control chain — relay, probe, PID/thermostat — so the number you set is the number you actually cook at. And once that’s under control, your food gets boring again in the best possible way: same result, every time.

‍