What Fault 21 Means
Where Fault 20 reports too little current through the damper flap heater, Fault 21 reports too much. F&P's recommended first step is to look for a short circuit in that heater, and to fit a new one if that is what the measurement shows.
Common Causes of Fault 21
- A short circuit within the flapper heater itself
- Moisture bridging the heater terminals inside the damper housing
- Chafed heater wiring shorting against the damper frame
🔧 One Safe Check You Can Try
Nothing safe to open up, but it is worth noting whether the code appeared after a hand defrost or after water was spilled inside the cabinet, because both put moisture where this small element lives.
⚠ Why You Shouldn't Go Further Than That
- Pull the plug before anything is opened, since this element runs from the mains side of the module and an over-current problem is the last thing to probe energised.
- Fitting a replacement without curing the moisture that caused the short simply hands the new element the same fate.
- The damper flap is set to a fixed seating clearance, and once it has been apart it rarely closes fully again without being re-shimmed.
- A short that has already been through the module may have damaged its switching side too, which only a proper check will reveal.
Opening a panel to inspect or repair something yourself doesn't automatically cancel your manufacturer's warranty — but it can risk accidental damage, and some manufacturers do have specific service conditions. Check your product's warranty terms, or ask us, before deciding.