Mineral buildup in heating circuits is common in London's water supply. Also, a failing thermostat or low coolant level reduces heat output. If heat works only after 10+ minutes of driving, suspect a stuck thermostat—critical to repair before winter arrives.

AC systems should be serviced every 2-3 years even in cold climates like London. During rare summer heat (80°F+), a non-functional AC can create unsafe driving conditions. Refrigerant leaks worsen yearly, so early detection prevents costly compressor failure ($800-$1,500).

A working defroster is essential for safety in London winters but shouldn't be your only tool. Use a frost shield at night, park in a garage if possible, and ensure your heater and defroster work at full capacity by September. A failing heater core reduces defrost efficiency by 50%.