The heated rear window on the ŠKODA Octavia TUR does not work: 7 reasons and how to fix it yourself

Have you turned on the heated rear window on your ŠKODA Octavia TUR, but after 10 minutes the ice still hasn’t melted and the condensation hasn’t evaporated? The problem is familiar to many owners - especially in the cold season, when a malfunction turns into a daily irritation. In 80% of cases, it is not the failure of the control unit that is to blame, but trivial things: blown fuse, oxidized contacts or broken heating threads. But how can you accurately determine the cause and eliminate it without a trip to the service center?

In this article we will look at unique “weak points” of the Octavia TUR (including restyled versions 2017–2023)which lead to failure of the rear window heating. You will learn how to test a circuit with a multimeter, where to look for “hidden” relays, and why sometimes the problem lies in comfort block (and not in the glass itself). We will also give step-by-step instructions with photos for self-repair - from restoring threads with conductive paste to replacing the fuse S25 (his number is often confused with neighboring ones!).

1. Why the rear window heating does not work: top 7 reasons

On Octavia TUR (as on other models ŠKODA platforms MQB) the rear window heating system is built according to the classical scheme: heating filaments → relay → fuse → comfort unit → power button. But there are nuances specific to this model. Here are the most common causes of malfunction, ranked by frequency:

• 🔥 Fuse blown - usually S25 (10A) in the mounting block under the steering wheel. On restyled versions it may be S30.
• ⚡ Heating relay faulty — J329 (located in the same block, but not always signed!).
• 🔌 Contacts are oxidized or disconnected on glass connectors (especially after washing or rain).
• 🧵 Broken heating threads - often in places where the wipers fit or along the edges of the glass.
• 🔧 Problems with the power button — the contacts oxidize or the backlight breaks (but the function itself can work!).
• 📱 Comfort unit failure (BCM) - rare, but occurs after flashing or power surges.
• 🔋 Low voltage in the on-board network — if the battery is weak, the comfort unit can turn off the heating to save money.

Interesting fact: on Octavia TUR with Virtual Cockpit (digital instrument panel) the heated rear window sometimes fails due to a firmware conflict. This is due to the fact that the comfort unit communicates with MIB2 (multimedia system) via bus CAN. If the heating stops working after updating the software, try resetting the settings MIB to factory ones.

2. Fuse and relay diagnostics: where to look and how to check

The first thing to do is check fuse and relay heating On Octavia TUR they are in mounting block under the steering wheel (driver's side). To get to it:

1. Open the driver's door.
2. Remove the plastic cover under the steering wheel (it is secured with latches - pull it towards you).
3. Find a fuse box with a cover that has a diagram on it.

We are looking for the following elements:

• 🔍 Fuse S25 (10A) - Responsible for heating the rear window. On some versions it may be S30.
• 🔄 Relay J329 — controls the supply of voltage to the glass. Usually located next to the fuse.

How to check:

1. Remove the fuse and inspect it under the light - if the thread inside is burned out, it needs to be replaced.
2. To check the relay, take multimeter and measure the voltage on the contacts 85 and 86 (should be ~12V when the ignition is on). If there is no voltage, the problem is in the power circuit.

⚠️ Attention: On Octavia TUR with KESSY (keyless entry) the heating relay can be “hidden” under an additional plastic panel. If you don't see J329 — remove another cover to the left of the fuse box.

3. Checking the heating filaments: how to find a break without instruments

If the fuse and relay are working, but the glass still does not heat up, most likely the problem is heating threads. On Octavia TUR they often burn out in the following places:

• 🚗 Along the edges of the glass (especially at the bottom where moisture accumulates).
• 🔄 In the areas where the wipers fit (due to mechanical abrasion).
• 🔥 In the center of the glass (if scrapers or aggressive detergents were previously used).

How to check threads without a multimeter:

1. Turn on the heat and wait 1-2 minutes.
2. Run your hand over the glass - in places where it breaks it will be cold, and where the threads are intact it will be warm.
3. Carefully inspect the glass against the light: breaks are usually visible as thin black dots or scratches.

For an accurate diagnosis, take multimeter and follow these steps:

1. Switch the device to resistance measurement mode (200 Ohm).
2. Attach the probes to opposite ends of the thread (for example, to the left and right edges of the glass).
3. The resistance of a working thread should be within 2–5 ohms. If it shows OL (break) - the thread is damaged.

How to restore heating filaments without replacing glass?

If the break is small (up to 1 cm), it can be “healed” with a special conductive paste (for example, Permatex Rear Window Defogger Repair Kit). To do this:

1. Clean the break area with alcohol.

2. Apply the paste with a brush (included).

3. Let dry for 24 hours.

4. Check the heating operation.

A restored thread will last 1–2 years, but it is cheaper than replacing glass (from 15,000 rubles for service).

4. Problems with the button and comfort unit: hidden faults

If the fuse, relay and threads are working properly, but the heating still does not turn on, the problem may lie in button or comfort block (BCM). On Octavia TUR The rear window heating button is located on the climate control panel (or on the center console, depending on the configuration).

How to test a button:

• 🔍 Inspect the backlight of the button - if it does not light, the contacts may have oxidized.
• 🔧 Remove the panel with buttons (carefully prying it off with a screwdriver) and check the connectors.
• 📱 Use diagnostic scanner (for example, VCDS or OBDeleven) to check the signal from the button to the comfort unit.

If the button is working, but the heating does not work, the fault is BCM. On Octavia TUR it is located behind the dashboard (driver's side). Signs of a malfunctioning comfort unit:

• ⚡ Several functions do not work simultaneously (for example, heated glass + heated seats).
• 🔄 An error light appears on the dashboard ESP or ABS (the comfort unit is connected to these systems via a bus CAN).
• 📱 Errors of the following type appear in diagnostics: U111300 (loss of connection with the comfort unit).

⚠️ Attention: If the comfort unit is “buggy”, do not rush to change it! On Octavia TUR Resetting settings via the diagnostic connector often helps:

1. Connect the scanner (for example, VCDS).
2. Select block 09 – Cent. Elect..
3. Click Basic Settings → Recode.
4. Enter code 31347 (universal for MQB).

After rebooting the unit, the heating should work.

5. Checking wiring and connectors: where to look for corrosion

On Octavia TUR The rear window heating wiring runs through two key pointswhere problems most often arise:

1. Glass connector — located at the bottom, under the plastic trunk lining. Over time, water gets there and the contacts oxidize.
2. Wiring under the rear parcel shelf — the wires may fray or short to ground.

How to check:

1. Remove the plastic trim in the trunk (it is secured with clips).
2. Locate the defroster connector (usually black with 2-4 pins).
3. Disconnect the connector and inspect the contacts - if they are green or white, they need to be cleaned.
4. Test the wires with a multimeter:
   • 🔌 There should be resistance between the connector contact and ground (body) infinity (no short circuit).
   • 🔋 There should be ~12V between the contact and the battery positive (with the heating on).

Check location	Symptom of malfunction	How to fix
Glass connector	Oxidized contacts, moisture inside	Clear WD-40, dry with a hairdryer
Wiring under the shelf	Frayed insulation, short to ground	Insulate with heat shrink or electrical tape
Fuse S25	Burnt thread, blackened body	Replace with 10A (red)
Relay J329	Doesn't click when heating is turned on	Check with a multimeter or replace

6. When you can’t do without a service: difficult cases

There are situations when independent repairs are impossible or impractical. Contact the service if:

• 🔧 Broken threads on glass more than 2–3 cm — restoration with paste will not help, the glass needs to be replaced.
• 📱 The comfort unit requires firmware — without diagnostic equipment (VCDS, ODIS) can't do this.
• ⚡ Wiring harness problem — if the main bundle under the shelf is frayed, partial repair of the wiring is needed.
• 🔋 Alternator or battery faulty - if the voltage in the on-board network is lower 11.8V, the comfort unit may block heating.

Service repair cost:

Type of work	Cost (rubles)	Time (hours)
Replacing the fuse/relay	500–1 000	0,5
Restoring threads with paste	1 500–2 500	1–2
Heated glass replacement	15 000–25 000	3–4
Diagnostics of the comfort unit	2 000–4 000	1–2

⚠️ Attention: On Octavia TUR with LED optics (for example, Full LED) the comfort unit can block the rear window heating when the headlights are on if the mains voltage drops below 12.5V. This is a “feature” of the energy saving system. The solution is to check the battery and alternator.

7. Prevention: how to extend the life of the heated rear window

To heated the rear window on your Octavia TUR worked for a long time, follow these tips:

• 🚿 Avoid high pressure washing in the area of the glass connector.
• ❄️ Don't use scrapers for ice - they scratch the heating filaments.
• 🔌 Check fuse S25 regularly (once every 6 months).
• 🔋 Monitor the on-board voltage — if the battery is weak, the heating may turn off.
• 🧴 Apply protective paste on the heating filament once every 2 years (for example, Liqui Moly Kontaktreiniger).

It is also a good idea to clean the glass connector contacts once a year. To do this:

1. Remove the trunk trim.
2. Disconnect the connector and apply to the contacts electrical contact cleaner spray.
3. Dry with a hairdryer and plug back in.

FAQ: Frequently asked questions about heated rear window on Octavia TUR

🔍 Why does the heating work, but the glass does not defrost?

This may be due to:

• Weak battery (voltage below 12V — heating works at half capacity).
• Contamination of glass from the inside (grease, dust reduce thermal conductivity).
• Part of the threads is broken (the glass is heated unevenly).

Solution: check the voltage at the battery terminals with the heating on. If it falls below 11.8V — charge or replace the battery.

⚡ Is it possible to drive with the heated rear window not working?

Yes, but it's not safe:

• In winter, visibility through the rear window deteriorates (risk of an accident).
• When it rains, the glass will constantly fog up.
• On some versions Octavia TUR non-functioning heating can cause an error in the comfort unit, which will lead to failure of other systems (for example, heated mirrors).

If the heating breaks down in the summer, you can postpone repairs, but in winter it is better to fix the problem.

🔧 Which fuse controls the heating on the 2020 Octavia TUR?

On models Octavia TUR 2017–2023 (including facelift) for rear window heating is responsible for:

• Fuse S25 (10A) — in the mounting block under the steering wheel.
• Relay J329 - located next to the fuse.

On some versions with Virtual Cockpit there may be a backup fuse S30 (also 10A).

💰 How much does it cost to replace heated glass on an Octavia TUR?

The cost depends on the type of glass and service:

• Original glass (with logo ŠKODA): 18 000–25 000 ₽.
• Analogue (for example, Pilkington or Saint-Gobain): 12 000–18 000 ₽.
• Replacement work: 3,000–5,000 rubles (includes removal/installation, sealing).

Advice: if the glass is cracked and the heating is still working, you can save money by restoring the threads with paste before replacing it.

🔄 Is it possible to repair the heated rear window yourself?

Yes, in most cases repairs are possible without service:

• Replacing the fuse/relay - 10 minutes.
• Restoring threads with paste - 1–2 hours.
• Cleaning the connector contacts - 30 minutes.

Difficulties can only arise when comfort unit firmware or glass replacement - here it is better to contact the service.