Webasto Thermo Top C Winterization: Complete Pre-Winter Checklist (2026)

Last updated: August 2026

Winter is the #1 killer of Webasto Thermo Top C heaters. This pre-winter checklist from IntelliGenParts Co. will keep your heater running reliably through the cold months.

Why Winterization Matters

Cold-weather failures account for 65% of all Thermo Top C problems. A 30-minute pre-winter service can prevent 80% of these issues.

Step 1: Replace the Glow Plug (15 minutes)

The glow plug is the #1 failure part in winter. Always replace before winter.

• 12V models: 91370B Glowpin – $14.90
• 24V models: 9005931B Glowpin – $14.90

Step 2: Check the Coolant (5 minutes)

Step 3: Inspect the Fuel System (10 minutes)

1. Check the fuel filter – replace if dirty
2. Inspect the 9024802A fuel pump – replace if 4+ years old
3. Use winter-grade diesel
4. Add anti-gel additive below -20C

Step 4: Test the Battery (5 minutes)

12V system needs minimum 11.5V during cranking. 24V needs 23.0V.

Step 5: Run a Test Cycle (15 minutes)

Before the cold hits, run the heater for 30 minutes. Watch for smooth ignition, steady flame, hot coolant, no unusual smells. See our error code guide if you see any faults.

Step 6: Clean the Combustion Chamber (20 minutes)

If your heater is 3+ years old, clean the chamber. If heavily corroded, replace the 92335D burner ($36).

Pre-Winter Shopping List

• 91370B Glowpin 12V – $14.90
• 9005931B Glowpin 24V – $14.90
• 9024802A Fuel Pump – $19.98
• U4847 Water Pump – $30

FAQ

When to start winterization?

September or early October. Don’t wait for the first frost.

Heater won’t start at -30C?

Check: 1) battery voltage, 2) glow plug (most likely), 3) fuel supply (anti-gel), 4) coolant concentration.

Drain coolant if storing RV?

Yes if temps drop below coolant’s freeze protection.

Need Winterization Parts?

All in stock at IntelliGenParts Co. with 1-year warranty. Browse complete parts collection.