Error F.76

Safety precautions:

1) If you smell gas or suspect a gas leak, evacuate the property immediately and call the gas emergency service. Do not try to fix the boiler yourself.

2) If you need to work near the boiler, isolate the electrical supply at the fused spur or mains switch. Only carry out non-intrusive checks. Do not remove covers or work on gas, electrical or sealed components unless you are a Gas Safe registered engineer.

3) Do not repeatedly force resets — continuous resetting can mask a serious fault and risks further damage.

Initial checks a homeowner can do (safe, non-intrusive):

1) Note when the fault occurs and any recent work: did this start after radiator/pipework work, power loss, or a period of very low external temperature (frozen condensate pipe)?

2) Check the boiler display and note the exact fault code and whether it clears after a restart.

3) Check the visible system pressure on the boiler gauge. If pressure is very low, the system may have lost water. Compare the reading with the recommended range in your manual; if unsure, do not attempt complicated repairs and call an engineer. If you are confident and familiar with your boiler, you may re-pressurise the system following the manufacturer’s instructions in the handbook; otherwise call a engineer.

4) Look for obvious external signs of trouble: water leaks beneath the boiler, dripping pressure relief valve, frozen/blocked condensate pipe (common in cold weather), or radiators that are cold despite the boiler running.

5) Listen to the boiler when it attempts to run: a silent pump when heating is demanded or a loud/noisy pump can indicate circulation problems.

6) If the condensate pipe is frozen, thaw it safely with warm (not boiling) water or a warm cloth; do not use open flames or electrical heaters against the pipe.

Basic reset and observation (safe steps):

1) Turn the boiler off at the control panel or the isolator switch, wait 2–5 minutes for it to cool and reset electronics, then turn it back on and see if the F.76 clears. Follow the reset instructions in the boiler manual rather than repeatedly pressing the reset button.

2) If the fault clears temporarily, monitor the system closely. Persistent or recurring F.76 means the underlying issue remains and must be investigated professionally.

Further diagnostic points to tell the engineer (do not open the boiler yourself):

1) Record when the fault started, what you were doing when it started (e.g., system bled, radiators replaced), and whether the fault is intermittent or permanent.

2) Note system pressure behaviour: does pressure drop over hours or days? Any visible leaks?

3) Note pump behaviour and any unusual noises or humming. Note if radiators heat unevenly or air bleeding was required recently.

4) If work was recently done on the heating system, confirm whether the P0 test and correct venting were performed before firing the boiler.

What a professional will check and likely do (for your information):

1) A Gas Safe engineer will inspect the wiring to the temperature sensor/thermal fuse, test the temperature sensor and thermal fuse continuity, and verify PCB inputs. They will test circulation (pump operation, possible seizure or blockage), check pressure sensor and filling loop operation, and examine the heat exchanger for internal blockages or damage.

2) If the thermal fuse has tripped or the heat exchanger is damaged, the engineer may need to replace the fuse, repair wiring, or replace the heat exchanger. Any internal work should only be carried out by a qualified engineer.

When to call a professional:

1) Call a Gas Safe registered heating engineer immediately if the F.76 does not clear with a controlled restart, if pressure is repeatedly low, if you find leaks, or if you are unsure of any checks. Do not attempt internal electrical or gas repairs yourself.

2) If the fault is intermittent but recurs, book an inspection sooner rather than later — repeated overheating can cause further damage.

Final note: F.76 is a serious protection fault. Safe, simple checks at home (visual leak checks, pressure check, thawing condensate, a single controlled reset) may identify or temporarily clear minor causes, but diagnosing and repairing the root cause — especially anything involving the thermal fuse, heat exchanger, gas or electrical components — requires a Gas Safe registered engineer.