How to Troubleshoot a Bosch Dryer That Won't Heat
A Bosch dryer that runs but produces no heat has different root causes depending on whether it is a heat pump model (WTW series) or a vented model (WTE/older WTG). Heat pump models have no traditional heating element — they use a compressor. Vented models have a resistive element that can burn out. This guide covers systematic diagnosis for both types.
Before You Start
- Tools needed: Multimeter, Torx T20 screwdriver (panel access), 400-grit sandpaper, vacuum with soft brush
- Parts needed: Depends on diagnosis
- Time required: 30-60 minutes for diagnosis
- Difficulty: Intermediate
- Safety warning: Unplug before any internal access. Wait 5 minutes for capacitor discharge on heat pump models. Do not open refrigerant lines on heat pump models.
Do You Have the Right Tools?
Gas leak detector ($130), thermal fuse tester ($95), belt tension gauge, and vent inspection camera ($180). Our technician arrives with $15K+ in professional tools — your diagnostic is free.
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Step-by-Step Instructions
Step 1: Determine Your Model Type
Heat pump (WTW series): no exhaust vent, has a condensate drain tank or plumbed drain. Operates on 120V. Uses a compressor — listen for a low hum similar to a refrigerator.
Vented (WTE/WTG): has an exhaust hose to the wall. Operates on 240V. Uses a resistive heating element in the exhaust path.
Step 2: Heat Pump Models — Diagnosis
Check 1: Is the compressor running? Start a cycle. After 2-3 minutes (compressor needs startup time), listen at the bottom-front of the machine. Low steady hum = compressor running (move to Check 2). Silence = compressor or inverter failure (professional repair needed, error E64 likely).
Check 2: Is the heat exchanger clogged? Open the kickplate. Pull out the heat exchanger (condenser). Inspect both sides — heavy lint blocks heat transfer. Vacuum gently with soft brush. Reinstall and test. This resolves 60-70% of heat pump no-heat complaints.
Check 3: Are the self-cleaning condenser nozzles blocked? Clean with vinegar on cotton swabs. Calcification blocks the automatic flushing system.
Check 4: Is the fan running? The fan circulates air through the heat pump circuit. If the fan motor has failed, heat builds up in the condenser but never reaches the drum. Listen for fan whoosh during operation.
Step 3: Vented Models — Diagnosis
Check 1: Is the element getting power? Test for 240V at the element connector during a heat cycle (LIVE TEST — extreme caution, or have professional do this). No voltage = control board relay or thermal fuse issue.
Check 2: Is the element intact? Disconnect and measure resistance: 15-25 ohms = good. Open circuit = burned out, replace. Ground fault (terminal to casing continuity) = shorted, replace and check vent.
Check 3: Are thermal fuses blown? Test for continuity — each should read 0 ohms. Open = blown. A blown fuse usually means the vent was restricted, causing overheating.
Check 4: Is the vent blocked? Disconnect vent hose and run a cycle with exhaust blowing freely. If heat returns, the vent is the root cause. Clean the entire vent path.
Step 4: Both Types — Sensor Check
If the dryer has heat but stops too early (clothes still damp), the moisture sensors are dirty — not a heating issue. Clean with 400-grit sandpaper. See the sensor cleaning guide for details.
Troubleshooting Decision Tree
- No heat + no compressor hum (heat pump) → Professional repair (E64 likely)
- No heat + compressor hums (heat pump) → Clean heat exchanger
- No heat + element open circuit (vented) → Replace element + check vent
- No heat + blown thermal fuse (vented) → Replace fuse + clean vent (root cause)
- Heat exists but cycle stops early → Clean moisture sensors
Safety First — Know the Risks
Gas dryers carry carbon monoxide and explosion risk. Even electric dryers involve 240V circuits that can deliver a fatal shock. Our techs are licensed and insured — let them handle the risk.
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Cost Comparison: DIY vs Professional
| DIY | Professional | |
|---|---|---|
| Diagnosis | $0 | $80-$120 service call |
| Fix (if cleaning) | $0-$5 | $80-$120 |
| Fix (if element/fuse) | $40-$80 | $180-$320 |
| Fix (compressor) | N/A — professional only | $400-$700 |
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The Real Cost of DIY
Average DIY attempt: $150-400 in tools you may use once, plus the risk of further damage. Our diagnostic visit costs $0 — we find the problem and give you an honest quote.
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FAQ
Q: My heat pump dryer was warm before but now it's cold — did something break? A: Most likely the heat exchanger is clogged with lint. The self-cleaning system handles most lint but not all. Pull out the exchanger and vacuum both sides. This resolves the majority of gradual heat loss complaints.
Q: Can a blocked lint filter cause no-heat? A: On heat pump models, a severely clogged filter restricts airflow enough to reduce heating efficiency significantly. Always clean the lint filter first before diagnosing deeper issues.
Q: Why does my vented dryer keep blowing thermal fuses? A: Restricted exhaust vent is the root cause 95% of the time. The element overheats when airflow is reduced. Clean the entire vent path from dryer to exterior wall — fuses will stop blowing.
Q: Is no-heat on a heat pump model expensive to fix? A: It depends. If it is a clogged condenser ($0 fix — just vacuum), that is free. If it is a compressor or inverter failure ($400-$700), it becomes a replace-vs-repair decision based on machine age.
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