What happens when
a temperature probe fails?
The probe is the most physically vulnerable part of any thermostat, sitting inside the enclosure with the animal. What the controller does when it dies varies enormously between brands.
Three things can happen, and the firmware decides which. The safest controllers detect the loss, fall back to a sensible strategy and alert you. Many simply shut the output off, leaving the enclosure to go cold — survivable in summer, dangerous in January. The worst behaviour is to treat a failed probe's reading as real: a sensor reporting an implausibly low value can drive the heater permanently on. Before you buy, find out which of the three your controller does.
How probes actually fail
- Cable damage. Chewed, trapped in a door, crushed under a heavy hide, or pulled hard enough to break a conductor inside intact-looking insulation.
- Moisture ingress. The tip is in a warm, humid enclosure, which is exactly the environment that finds any gap in a seal. Misting systems accelerate it.
- Connector corrosion. Where the probe meets the unit, especially in a humid reptile room with ventilation nobody optimised.
- Age and thermal cycling. Years of heating and cooling work joints loose.
Intermittent failures are the hardest. A probe that reads correctly most of the time and spikes occasionally will not look broken in a glance at the app, but it causes the output to respond to readings that never happened.
The three behaviours, and what each costs
Shut the output off. The common approach, and the easy one to implement. The enclosure cools to room temperature. For a tropical species in an unheated room in winter, that is a serious problem, and it is made worse by the fact that most such controllers do not tell you.
Trust the reading anyway. The dangerous one. Several sensor types fail toward a specific value rather than toward nothing, and a controller that does not range-check will act on it. If the failure value is low, the thermostat concludes the enclosure is freezing and commands full heat indefinitely.
Detect, fall back, and alert. What you want. The controller recognises the reading as implausible rather than cold, switches to a strategy that does not require that probe, and tells you immediately.
Readings that mean “broken”, not “cold”
Learn what your sensor reports when it fails. Common digital probes have characteristic values — a fixed number at the bottom of the range on an open circuit, or a default value latched at power-on that never updates. A reading that is implausible for a room containing a living animal, or one that is frozen to two decimal places across hours of history, is a dead probe rather than a cold enclosure. The history graph is where this is most obvious: real temperature is never perfectly flat.
Reducing the odds
- Route the cable where it cannot be chewed or crushed, and secure it so pulling the enclosure does not pull the probe.
- Keep the connector out of the humid zone where you can, and inspect it when you do routine maintenance.
- Do not bury an unrated probe in damp substrate and expect it to last.
- Keep a spare. Probes are inexpensive next to the animal, and a failure you can fix the same evening is a different problem from one that waits for a delivery.
- Check history for flatlines occasionally. A probe that has quietly stopped updating is easiest to catch on a graph.
How the Ectoscale 6 handles a dead probe
The zone does not simply shut off and let the enclosure go cold. Heater 1 falls back to the duty cycle it learned from its own history — the proportion of time it had been running to hold that enclosure at target, which is a far better estimate than either full on or full off. Heater 2 switches to the ambient sensor with its own dedicated setpoint, so it keeps regulating against a real measurement rather than a missing one.
The on-unit display shows LIMP for as long as the condition lasts, and the fallback is announced through Telegram rather than left for you to notice. It is a holding pattern, not a fix — it is designed to keep the animal safe until you can get a probe into it.
A dead probe should not mean a cold enclosure
Learned duty-cycle fallback, an ambient-sensor alternative, LIMP on the display and an alert on your phone.