Boiler
F.72
The F.72 error code on a Worcester Bosch boiler indicates a persistent discrepancy between the flow and return temperature sensors, and it’s a fault that will lock out your boiler until it’s resolved — don’t ignore it.
What does this error mean?
Your boiler constantly monitors the temperature of water flowing out to your radiators (flow) and returning back (return). The F.72 fault means the boiler’s control board has detected that these two sensor readings are too close together or contradicting each other over a sustained period, suggesting a measurement or circulation problem. This is distinct from the F.22 or F.28 codes — F.72 specifically points to a sensor offset or NTC thermistor mismatch rather than a simple pressure or ignition issue.
Est. repair cost
£150–£400 for NTC sensors or pump replacement; up to £600 for PCB — all requiring a Gas Safe engineer
🔍 Likely causes
🛠️ Step-by-step fix
Step 1 — Reset the boiler: Press and hold the reset button (usually marked with a flame and cross symbol) for 3–5 seconds. If the boiler fires up and runs without returning the F.72 code within 24 hours, monitor it closely but no further action may be needed immediately.
Step 2 — Check your boiler pressure: If the pressure gauge reads below 1 bar, top up via the filling loop to 1–1.5 bar. Low pressure can cause circulation issues that trigger this fault.
Step 3 — Bleed your radiators: Air in the system reduces circulation efficiency, which can affect temperature readings. Bleed all radiators starting from the ground floor upward, then re-check boiler pressure.
Step 4 — Do not attempt sensor or PCB work yourself: Replacing NTC sensors, checking internal wiring, or diagnosing PCB faults on a gas boiler requires a Gas Safe registered engineer. This is not a DIY job — gas appliance internals must only be worked on by a qualified professional.
Step 5 — If the code returns after a reset, call a Gas Safe engineer: Provide them with the exact error code (F.72) and describe whether the fault appeared suddenly or built up over time. This helps them bring the right parts — likely NTC sensors or a pump.
📞 When to call a professional
Call a Gas Safe registered engineer immediately if the F.72 code returns after a reset, if your boiler is producing no heat or hot water, or if you notice any unusual smells or sounds alongside the fault. Tell the engineer: ‘My Worcester Bosch is showing error code F.72 — I suspect a flow or return NTC sensor fault or a circulation issue.’ This gives them a head start on diagnosis.
⚖️ Repair or replace?
NTC sensor replacement typically costs £150–£300 including labour; a pump replacement runs £200–£400; a PCB replacement can reach £400–£600 fitted. If your Worcester Bosch boiler is over 10–12 years old and facing a repair bill above £400, replacement with a new A-rated boiler (typically £1,800–£3,000 installed) is often better value long-term. Boilers under 8 years old are almost always worth repairing, especially if under a Worcester Bosch warranty or service plan.