MEDIUM RISK
Common symptoms
- See page for quick checks
Cost expectations
Typical costs vary by car and region. Use this as a ballpark.
- DIY / parts: £20–£80
- Garage / labour: £80–£250
Most likely causes (ranked)
Start at the top. Rule out the common, cheap causes before expensive ones.
- Low coolant / airlock
- Thermostat stuck open
- Heater core blockage
- Blend flap actuator fault
- Water pump flow issues
Quick checks (fast, low-cost)
Fast checks you can do with basic tools before buying parts.
- Check coolant level and bleed system properly.
- Ensure engine reaches normal temp.
- Feel heater hoses for temperature difference.
- Check HVAC settings and actuator movement.
- If overheating present, stop and diagnose cooling system.
Recommended tools
These tools make diagnosis faster and stop you buying random parts.
Related fixes
If your symptoms don’t match perfectly, check these next.
What to do next
- Fix coolant issues first; don’t ignore overheating.
- If heater core blocked, flush or replace.