F11 flow/return NTC thermistor fault
F25 CH temperature difference between flow & return too high during operation
BOTH these faults indictate a circulation problem during CH operation
Boiler is OVERHEATING when CH ON
Why is boiler OVERHEATING when CH ON?
System sludge?
Pump defective?
Excessive air in system?
Poor system layout leading to poor system circulation?
Etc etc
Could be any number of reasons
I'm afraid you will need a gas engineer on site to
INVESTIGATE FAULT
DIAGNOSE FAULT
& REPAIR FAULT
Anon
December 2018
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