BoilerFaultCodes.com
7C Medium Lockout

Your boiler has lost power while trying to clear an old error, or the reset button wasn't held down for long enough.

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: Mains supply failure during locking error or reset button released too soon.

What causes this fault?

This fault happens when the boiler's electrical supply is interrupted at the exact moment the computer is trying to process a previous error. It can also be triggered if the reset button is released too quickly, preventing the system from finishing its safety checks. Essentially, the boiler has become 'confused' during a restart and needs a stable connection to clear its memory.

Typical repair cost £0-120 (including labour)

DIY fix possible

Press and hold the reset button firmly for a full 3 to 5 seconds.Ensure your main electrical supply or fuse spur hasn't been tripped or turned off during the reset process.Restart the boiler and wait to see if the display returns to normal operation.

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →

Protect yourself from future repair bills

A boiler cover plan would cover faults like 7C — no call-out fees, no surprises.

Top rated
OpenFix
Boiler & heating care plans
Get a quote →
Hometree
from £12.95/month
Get a quote →
HomeServe
from £8.00/month
Get a quote →

Affiliate links — we may earn a commission at no extra cost to you.

Ideal Maximiser SE is discontinued — time for a new one?

Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.

UK's #1 online installer
Boxt
Fixed-price online quotes. Next-day installation.
Get a free quote →
Heatable
Instant online boiler quotes from £1,499.
Get a free quote →
iHeat
Fast installation. Price match guarantee.
Get a free quote →

Affiliate links — we may earn a commission at no extra cost to you.

Related fault codes