Heating System No Heat Fault Guide

Heating System No Heat Fault Guide

Purpose

To systematically identify why a heating system is not calling for heat or not firing the boiler.

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1. Initial Checks

• Confirm system has power (boiler, programmer, controls)
• Check programmer is set to ON or timed correctly
• Check thermostat setpoint is above room temperature
• Check for any obvious error codes on boiler

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2. Confirm Demand Signal

• Increase thermostat temperature
• Listen/observe for system response:

 * Valve movement (if present)
 * Relay clicks in wiring centre
 * Boiler ignition attempt

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3. Check Controls

• Room thermostat operation
• Programmer output (heating channel ON)
• Smart thermostat receiver status (if fitted)

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4. Check Zone Equipment

• 2-port valve opening (S-Plan)
• 3-port valve movement (Y-Plan)
• End switch operation sending boiler signal

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5. Boiler Demand Check

• Confirm switched live reaching boiler control terminal
• Check boiler enable input is present
• Verify no internal boiler lockout

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6. Electrical Fault Isolation

• Check for loose neutrals in wiring centre
• Check for broken switched live circuits
• Check for failed relay outputs in controllers
• Check fused spur supply integrity

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7. Common Real-World Causes

• Failed motorised valve actuator
• Stuck valve not opening fully
• Thermostat not calling correctly
• Broken switched live wire
• Wiring centre terminal loose connection
• Smart thermostat receiver failure
• Boiler interlock missing or bypassed

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8. Conclusion

Most no-heat faults are caused by control signal failure, not boiler faults. Always trace demand from thermostat → valve/controller → boiler.