BoilerFaultCodesYour boiler has detected that the temperature is not rising as expected when the burner is lit, which usually means there is a lack of water or a sensor issue.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Flow and or return temperature sensor error
What causes this fault?
This fault occurs when the boiler fires up but the sensors don't detect a corresponding rise in temperature, leading the system to believe there is no water to heat. The most common reason is a low water level or air trapped in the system, though it can also be caused by sensors that have become unclipped or faulty.
DIY fix possible
Check the pressure gauge on the front of the boiler is between 1.0 and 1.5 barIf the pressure is low, use the filling loop to top it up to 1.5 barOnce the pressure is correct, press the reset button (indicated by a flame with a cross through it)
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like F.83 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
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.
Affiliate links — we may earn a commission at no extra cost to you.