BoilerFaultCodesWhat the manual says
Manufacturer manualFlow Thermistor Fault
From this model's manual
Verified against the Ideal Logic Max Heat installation & service manual.
What causes this fault?
This fault occurs when the internal sensor responsible for tracking the temperature of the water leaving your boiler has failed or is sending garbled data. The most common reason is that the sensor's electrical resistance has drifted out of range due to age, or a loose connection in the wiring is preventing the control board from receiving a steady signal.
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.
Find a Gas Safe engineer
Search the official register →
Boiler cover options
Avoid the next call-out bill
A cover plan would handle faults like 4.8: no call-out fees, no surprise bills.
Approved partner
Get a quote →
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Affiliate links. We may earn a commission at no extra cost to you.