Thermostat or receiver emits a buzzing or humming noise during operation.

Safety first: Buzzing components are often at mains voltage. Isolate power before opening the receiver.

Steps to investigate:

• 1. Identify source: Listen closely to determine whether the noise comes from the thermostat, receiver, or boiler.
• 2. Check mounting: Ensure the receiver is firmly fixed to the wall and not vibrating against loose panels or pipes.
• 3. Inspect components: With power off, open the receiver and look for loose transformers or relays. Tighten mounting screws if accessible.
• 4. Monitor temperature: If buzzing is accompanied by overheating or burning smell, keep the system off and seek immediate professional help.

When to call a professional: Persistent or loud buzzing may indicate a failing relay or transformer; replacement by a heating engineer is recommended.