Editing Heating Fault Decision Tree (Core Diagnostic Flow)

= Heating Fault Decision Tree =

== Purpose ==
To quickly identify whether a heating fault is caused by controls, wiring, or the boiler itself.

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== Step 1: Identify Symptom ==
* No heating at all
* No hot water
* Intermittent heating
* Heating stuck ON
* Boiler not firing

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== Step 2: Check Demand Exists ==
* Raise room thermostat above ambient temperature
* Check programmer is calling for heating/hot water
* Observe:
** Valve movement
** Relay clicks
** Boiler attempt to fire

IF NO DEMAND:
→ Control issue (thermostat/programmer/wiring)

IF DEMAND PRESENT:
→ Move to Step 3

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== Step 3: Check Zone Operation ==
* 2-port valve opens? (S-Plan)
* 3-port valve moves correctly? (Y-Plan)
* End switch activates?

IF NO MOVEMENT:
→ Valve or actuator fault

IF MOVEMENT BUT NO BOILER FIRE:
→ Electrical interlock fault

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== Step 4: Check Boiler Signal ==
* Verify switched live present at boiler terminal
* Check boiler enable input
* Confirm no internal lockout

IF NO SIGNAL:
→ Wiring/control issue upstream

IF SIGNAL PRESENT:
→ Boiler fault likely

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== Step 5: Final Isolation ==
* If controls and wiring are correct:
→ Treat as boiler-side issue
* If signal missing or incorrect:
→ Control system fault confirmed