BoilerFaultCodes 703 Medium Warning
Your boiler is struggling to monitor the temperature for one of your heating zones, which may cause that specific area of your home to not heat correctly.
Book a service
This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.
Technical description: Send sensor defective (Zone 3)
What causes this fault?
This fault occurs when the boiler is unable to read the temperature data from the specific sensor responsible for your third heating zone. The most common cause is a failure of the internal thermistor (NTC sensor) or a loose connection in the wiring harness that links the sensor to the main control board.
Typical repair cost £100-180 (including labour)
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like 703 — no call-out fees, no surprises.
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