Overview
The F7 fault on Ideal Logic Max / Logic Plus boilers means the boiler has detected low mains voltage or an unstable electrical supply. The boiler’s control electronics monitor the incoming mains and will display F7 when the voltage falls below the safe operating threshold or fluctuates excessively. A persistent low-voltage condition can prevent the boiler from running correctly and may trigger protective shutdowns to protect the control board and other components. Severity ranges from moderate to high depending on the cause. If the problem is a temporary dip in supply (for example due to a local transient or heavy-load appliance starting), a simple restart may clear it. If the mains supply is genuinely low or the boiler’s fused isolation, wiring or PCB is faulty, the issue can recur and risks damaging electronics or causing loss of heating and hot water. Basic visual checks and a single controlled reset are reasonable for a homeowner, but electrical testing, internal wiring and any repairs to electrical components or gas-side parts must be done by a qualified electrician or a Gas Safe registered engineer. If the supply is confirmed low, contact your electricity supplier or network operator immediately.
Troubleshooting Steps
Safety precautions:
- Do not touch live wiring or internal electrical components unless you are a qualified electrician. Turn off the boiler at its external isolator switch and at the consumer unit before attempting any inspection that requires opening covers. If in doubt, call a professional.
- Do not attempt gas-side or burner repairs yourself. Any work on gas or sealed components must be done by a Gas Safe registered engineer.
- Avoid repeated resets: do not reset the boiler more than five times within 15 minutes; excessive restarts can create additional lockouts.
Initial checks a homeowner can do:
1. Note the exact display and when the F7 appears (continuous, intermittent, after turning on other appliances, during storms, etc.). Take a photo of the display for reference.
2. Check other electrical devices in the house: are lights dimming, other appliances running poorly, or are multiple items losing power? If yes, this points to a wider mains supply problem.
3. Check your consumer unit (fuse box) for any tripped MCBs or blown fuses and reset only if it is safe to do so. Check the boiler’s fused spur or isolator is switched on.
4. Turn off high-draw appliances (e.g., electric showers, ovens, EV chargers) and try restarting the boiler once. If the fault clears when heavy loads are removed, load-related voltage dips may be the cause.
5. Try a controlled boiler restart: put the boiler in standby, wait a minute, then restart following the boiler manual’s reset instructions. If the fault clears and does not return, monitor for recurrence.
Specific diagnostic steps and fixes:
1. If other home electrics show problems or the F7 persists after restart, contact your electricity supplier or distribution network operator to report a suspected low-voltage supply or intermittent supply issue. They can check the incoming supply and advise or arrange repairs.
2. If your supplier confirms mains voltage is normal but the boiler still shows F7, do not attempt internal electrical repairs yourself. The likely next steps are:
- A qualified electrician should check the supply voltage at the boiler terminals with the correct voltage meter. Typical UK nominal mains is ~230–240V; many control boards will report a fault if voltage drops below a lower threshold (commonly around ~185V). Only a competent person should perform this measurement.
- The electrician should inspect the fused isolator, the spur, and the incoming wiring for loose connections, corrosion or damage and repair as necessary.
3. If the supply and wiring at the boiler are OK, arrange for a Gas Safe registered engineer to inspect the boiler. Persistent F7 can also be caused by internal faults (PCB errors, fan or fan wiring faults, pressure/air switch faults or other component failures) that require boiler-specific diagnostics and safe replacement of parts.
4. If the boiler has recently been serviced or parts replaced, tell the engineer that history — PCB configuration issues or incorrect installations can sometimes produce similar faults.
When to call a professional:
- Call your electricity supplier or network operator immediately if multiple appliances are affected, lights are dimming, or you suspect the external mains supply is low or unstable.
- Call a qualified electrician to inspect and test the incoming supply and boiler electrical isolation if the issue appears local to your property wiring.
- Call a Gas Safe registered heating engineer to inspect the boiler if supply and wiring are confirmed OK or if the F7 persists after electrical checks; they will safely test the boiler electronics, fan, sensors and PCB and replace faulty boiler components if required.
Important reminders:
- Do not attempt internal electrical or gas repairs yourself.
- Keep a record (time/date, behavior, any household electrical events) to help engineers and your electricity supplier diagnose intermittent issues.
- If you are in any doubt about safety, switch the boiler off at the isolator and seek professional help.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Ideal Logic Max System / Logic Plus System.