BoilerFaultCodesYour boiler is struggling to detect a proper temperature change between the pipes, which usually means there is not enough water moving through the system to heat your home properly.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical 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.
DIY fix possible
Check the pressure gauge on the front of the boiler and top it up to 1.5 bar if it is lowEnsure all radiator valves and isolation valves under the boiler are fully openBleed your radiators to remove any trapped air that might be blocking water flow
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A boiler cover plan would cover faults like F.83 — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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