TH DGH FC8 FC17 FC18 - Condensate pressure switch
 
FC8 - Condensate pressure switch closed at start (5 star)
FC17 - Condensate detected during run (5 star)
FC18 - Condensate detected at start (5 star)

Click here to view YouTube video Spectrolink SCC accessing and clearing fault code history



How the condensate pressure switch works:

  • Pressure switch is checked at startup to ensure it is open ( suction fitting not blocked) before combustion fan starts at startup. If it is closed a FC8 reported
  • If open combustion fan starts and the suction created in the flue pan causes the suction pressure switch to operate and close its contacts.
  • Whilst the flue pan remains free of condensate and the combustion fan is running the pressure switch will remain in due to fan suction and its contacts closed and all is well
  • Should the pan fill with condensate and block the condensate suction nipple this will result in the suction from the fan no longer holding in the condensate pressure switch it will drop out and a FC18 reported



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If FC18 issue still persists after confirming that the unit is level, there are no blockages in the condensate pressure switch hoses, and the unit is draining correctly, try replacing the condensate pressure switch (Part #639826). Over time, the microswitch on the 18pa pressure switch, despite sounding operational, may have contamination on its electrical contacts, causing sticking issues.




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Check the silicon tube from condensate pressure switch to the condensate drain tray isn't excessive in length to create a low
point that can cause condensate to block to tube and trigger a FC18

Below image shows an incorrect routing of the silicon tube

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Check the silicon tube from condensate pressure switch to the condensate drain tray isn't excessive in length to create a low
point that can cause condensate to block to tube and trigger a FC18

Below image shows is the correct routing of the silicon tube

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Check the small breather hole on the pressure switch 18 Pa (for condensate) circled in red below is clear and is not covered by silicon/rubber pressure switch hose. This hole must not be blocked or covered!!!





If FC18 issue still persists after confirming that the unit is level, there are no blockages in the condensate pressure switch hoses, and the unit is draining correctly, try replacing the condensate pressure switch (Part #639826). Over time, the microswitch on the 18pa pressure switch, despite sounding operational, may have contamination on its electrical contacts, causing sticking issues.