SH18 SH25 WF25 - FC7 service diagnostic fault finding

 
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FC7 - Ignition failure after 3 x ignition attempts 

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If heaters burners ignite but spark continues for approximately 7 seconds and then burners extinguish the flame is not being sensed
– Therefore, most important is to check signal strength. 
If flame sense signal is low investigate the electrode and and flame sense leads

  • Check signal strength with a multi meter set to DC voltage
  • Start heater and when flame cross ignites and is present at the flame sense electrode, measure DC voltage across metal terminals FC- and FC+ on the EFS (Fenwal). 

A reading of 1.5 to 2 Volt DC is considered good signal strength. Any values below 1 Volt DC need to be investigated and rectified.


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FC7   after the burners ignite but extinguish after 2 to 3 seconds can be caused by recirculation of combustion products into combustion air inlet
Check the flue has been installed correctly paying particular attention to the flue terminal fitment - see below for guidance on flue terminal fitment
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