Error F7

Safety precautions:

1) Do not remove the boiler cover or touch internal components unless you are a qualified, authorised engineer. There are live mains connections and gas components inside.

2) If you need to isolate power to the boiler for safety, turn off the dedicated boiler isolator switch or switch off the circuit breaker in the consumer unit. Call a qualified electrician for any work on mains wiring. For any gas-side work or if the boiler remains locked out, call a Gas Safe / registered engineer.

Initial checks a homeowner can do (no internal access required):

1) Check the mains power to the property: are other appliances and lights working normally? If multiple appliances are failing or lights are dim, the issue is likely with the incoming supply and you should contact your electricity provider.

2) Check the boiler mains isolator/switch is ON and the fuse or breaker for the boiler circuit in the consumer unit has not tripped. Reset a tripped breaker and try restarting the boiler via the Restart button. If a domestic fused spur is fitted, check its fuse.

3) If the boiler is supplied from a fused plug (rare), check the plug and fuse. If it is hardwired, check the consumer unit only. Note any pattern of the fault (intermittent, only when other heavy loads are on, after storms, etc.).

4) Press the boiler Restart button as described in the manual. If the fault clears and does not return, monitor the boiler for stability. If F7 returns, proceed to the next steps.

Specific diagnostic steps and fixes (professional actions recommended):

1) If basic checks did not solve it, contact a qualified electrician to measure the incoming mains voltage at the consumer unit and at the boiler supply terminal. A sustained voltage below nominal (~230V, typically under ~180–190V depending on manufacturer thresholds) confirms undervoltage. The electrician can also check for loose/overheated terminals, poor neutral/earth connections, and correct polarity.

2) If the electrician finds the property supply voltage is low, contact the electricity distribution network operator / supplier to investigate (they can check supply transformer/load issues). If low voltage only when high loads run, consider redistributing heavy loads or having the supplier investigate network capacity.

3) If the supply at the consumer unit is normal but low at the boiler, have the electrician inspect and test the boiler circuit: check the isolator switch, wiring continuity, connections at the fused spur/consumer unit and at the boiler terminal block. Tighten or replace any damaged terminals or cabling.

4) If the mains supply and wiring are verified OK, the fault may be internal to the boiler (power supply module or PCB). Do not attempt internal repairs yourself. Arrange a Gas Safe registered engineer who can carry out safe isolation, remove the cover, test voltage at the boiler internal input, check the boiler PSU/regulator and PCB for faults, and replace defective parts if needed.

5) If the engineer replaces parts or performs repairs, request they check for any collateral damage (e.g. failed fan or pump caused by undervoltage), and confirm the boiler is safe and correctly commissioned before leaving.

Additional advice and record keeping:

1) Note times and conditions when F7 occurs (time of day, weather, when heavy appliances are on). This information helps the electrician and supplier diagnose intermittent supply dips.

2) Keep the boiler model and serial number to hand when contacting Keston, your installer or utility provider.

3) If you see other fault codes or repeated lockouts (many restarts), stop attempting restarts and call a professional to avoid further damage.

When to call a professional:

1) Call a qualified electrician if any live-electrical testing, wiring inspection, or consumer unit work is required, or if you suspect the supply is unstable.

2) Call a Gas Safe registered engineer (or RGII in Ireland) for any internal boiler diagnosis or repairs, or if the F7 fault persists after external supply and wiring checks. If the electricity provider confirms a supply issue, coordinate between the supplier, electrician, and boiler engineer to resolve the fault before returning the boiler to service.

Important: do not attempt to bypass safety interlocks or continue using the boiler if F7 persists. The fault indicates an unsafe electrical condition for the boiler and must be resolved by qualified persons.