Combi Boiler Control Wiring Reference Pack

Combi Boiler Electrical Control Wiring Reference

Overview

Combi systems do not require external hot water control. Heating demand is sent directly to the boiler.

Main Components

• Combi boiler
• Room thermostat or smart thermostat
• Optional external programmer
• Fused spur supply
• Boiler control terminals (heating demand input)

---

System Operation

• Boiler fires when it receives a heating demand signal.
• No cylinder or zone valves required.
• Internal diverter valve controls hot water production.

---

Wiring Concept

• Thermostat switches heating demand input on boiler
• Boiler provides internal control logic
• Live supply via fused spur

---

Key Wiring Points

• Permanent live and neutral supply to boiler
• Switched live from thermostat/programmer to demand terminal
• Earth continuity mandatory
• Smart thermostats may require receiver module

---

Common Fault Areas

• No heating demand signal
• Incorrect thermostat compatibility
• Boiler not receiving switched live
• Incorrect link terminals left in place
• Faulty receiver module (smart controls)
• Loose connections at boiler terminals

---

Notes

• Always check manufacturer boiler terminal layout.
• Some boilers require internal links to be removed when controls are fitted.