BoilerFaultCodesTechnical description
Fault: NTC temp. gradient Temperature difference between flow and return temperature sensor is too small. Check: Flow/return temperature sensor (function, correct thermal connection), sufficient water volume.
What causes this fault?
This fault occurs when the boiler fires up but the sensors don't see the temperature of the water rising as quickly as expected. The most common reason is a lack of water pressure or a blockage that is preventing the water from flowing through the internal pipes fast enough to be measured correctly. In some cases, it simply means the sensors have become unclipped or have developed a fault, losing their ability to track the heat.
This issue often surfaces in autumn when the heating is turned back on for the first time, as pump blockages or air pockets are more likely to have formed during the summer break.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.