Heating System No Hot Water Fault Guide

Heating System No Hot Water Fault Guide

Purpose

To identify why domestic hot water is not being produced in a heating system.

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1. System Type Confirmation

• Combi boiler (no cylinder)
• System boiler (with cylinder)
• Heat-only boiler

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2. Combi Boiler Checks

• Check flow rate demand (tap fully open)
• Check for ignition attempt
• Check for boiler error codes
• Check inlet pressure and filters (if applicable)

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3. Cylinder System Checks

• Check programmer hot water ON setting
• Check cylinder thermostat setting
• Check motorised valve operation (hot water zone)
• Confirm end switch signal to boiler

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4. Electrical Control Checks

• Hot water channel output from programmer
• Cylinder thermostat switching correctly
• Valve actuator receiving supply
• End switch completing circuit to boiler

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5. Common Faults

• Failed cylinder thermostat
• Stuck hot water zone valve
• Broken actuator motor
• Incorrect programmer settings
• Wiring fault in junction box
• Boiler not receiving demand signal

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6. Notes

Hot water faults are usually control-side issues before being boiler faults. Always confirm demand signal first.