Most Likely Cause#
A Bosch washer that will not heat the water is most often the victim of a burned-out heating element — the immersion heater at the bottom of the tub that warms the wash. When it fails open, warm and hot cycles run cold. The next most common cause is the NTC temperature sensor misreading the water, which can fool the board into thinking the water is already hot. A control-board heater relay, a wiring or connector fault, and, over time, calcium scale insulating the element round out the list.
First, confirm the washer truly is not heating and it is not just a cold-by-design cycle. Bosch machines run many eco and cold cycles that never heat on purpose. Select a hot or sanitary cycle, let it run into the wash phase, and feel the door glass — if it stays cold on a cycle that should be hot, you have a real heating fault.
Confirm It Really Isn't Heating#
- Choose a cycle that should clearly heat — a hot wash or sanitary program, not eco or cold.
- Let it reach the wash phase, then carefully touch the door glass; a hot cycle warms it noticeably.
- If it stays cold, or clothes come out cold and detergent is undissolved, the heating circuit is at fault.
Do You Have the Right Tools?
Bearing puller set ($120), drum spider wrench ($85), multimeter ($85), and diagnostic software. Our technician arrives with $3,000+ in professional tools — your diagnostic is free.
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What Usually Causes It#
The table ranks the causes from most to least common on Bosch washers.
| Cause | Why it won't heat | How common | First fix |
|---|---|---|---|
| Heating element burnout | The element has failed open and cannot warm the water | Most common | Test the element for continuity; replace if open |
| NTC temperature sensor fault | A misreading sensor tells the board water is hot | Common | Test the sensor's resistance; replace if out of range |
| Control-board heater relay | The relay that powers the element has failed | Occasional | Test the board's heater relay |
| Wiring or connector fault | A loose or corroded connection breaks the heat circuit | Occasional | Inspect and re-seat the element wiring |
| Calcium scale insulation | Hard-water scale coats the element, cutting heat output | Least common | Descale; replace a heavily scaled element |
Heating Element#
Because it is the top cause, the element is the first thing to test. It is an electric heater immersed in the tub sump; when its internal wire burns through, the circuit goes open and no heat is produced, though the cycle otherwise runs normally. With the power off, disconnect and test the element for continuity — an open reading confirms a burned-out element, which is a defined part to replace. While it is out, check it for a thick chalky scale coating, since heavy scale insulates the element and steals heat even before it fails outright.
Sensor, Relay, and Wiring#
If the element tests good, the NTC temperature sensor is next. This sensor reports the water temperature to the board; when it drifts and reads too warm, the board decides no heating is needed and skips it, so the wash runs cold. Testing the sensor's resistance against its specification reveals a bad one. Less often, the fault is the control-board heater relay that switches power to the element, or a loose, corroded wiring connection in the heater circuit — inspect and re-seat those connections before condemning the board.
Quick Diagnostic Sequence#
- Confirm the fault on a genuine hot or sanitary cycle, not an eco or cold one.
- With the power off, test the heating element for continuity.
- Inspect the element for heavy scale and descale if needed.
- Test the NTC temperature sensor's resistance.
- Check the heater wiring connections and the control-board relay.
Safety: unplug the washer before testing the heating element or sensor. The element runs on line voltage and sits in water at the tub base, so verify the power is off and the machine is drained before reaching it.
Safety First — Know the Risks
High-voltage components and pressurized water lines create flood and shock risk. A single loose fitting can cause thousands in water damage. Our techs are licensed and insured — let them handle the risk.
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Repair or Replace#
A heating element and an NTC sensor are both moderate, well-defined parts, and descaling is nearly free, so a Bosch washer that will not heat is usually worth repairing. The costlier case is a failed control-board heater relay, and on an older washer a confirmed board fault is the point to weigh a repair against replacement. If you would rather not test line-voltage parts, you can book a diagnostic visit to have the element, sensor, and board checked.
Appliance Repair Technician · 8 years experience
Experienced technician with 8 years specializing in dishwasher repairs and European appliance brands including Bosch and Thermador.
