Some UK indoor units keep the display dark until you press a button, and some remotes have a light button that hides the lamps on purpose. A blank display with a fan that still runs is often that feature or a failed indicator, not a dead system. A blank display with no fan, no beep and a silent outdoor unit is power: rotary isolator, breaker, or a recent power cut. You can press a single button, check batteries, and look at the isolator handle without opening it. If nothing wakes after a proper wait, or a burning smell or a trip is involved, stop. Do not open the indoor panel to meter the board, and do not open the gas circuit.
A bedroom lamp switched off on purpose
Bedroom installs often have a display toggle because a bright setpoint annoys people at night. The icon is on that remote only. Pressing every key will change modes while you hunt it, so use the manual for the light key, or press on/off once and see if the fan responds even with the lamps dark.
A handset screen that died in a cold room
A remote with its own screen can go blank from batteries while the wall unit is fine. Replace the cells before you condemn the indoor display. If the handset screen returns and the indoor unit accepts on/off, you do not have a power fault. A new remote fixes a blank indoor display only if the indoor unit still runs and the problem is the handset screen. A remote cannot power a unit that has no supply.
Isolator, breaker, and the wait after a cut
Check the rotary isolator and whether the dedicated breaker has opened. After a UK power cut, wait several minutes and try one on command. Look at other sockets in the house only to see if the outage is whole-home. Do not remove the indoor fascia to watch LEDs on a board. HSE electricity guidance is to leave covers on. One try is enough.
A multi-split head with the outdoor supply off
Some multi-splits show nothing on an indoor head when the outdoor unit has no supply. The head is not independently useful. Confirm outdoor power before you assume the indoor display has failed on its own. Energy Saving Trust's air-to-air page is about the heat pump pair, which needs that outdoor supply before any indoor lamp matters. Say whether the fan still answers.
Stop when the blank panel is a dead supply
If the lights are out because a breaker tripped, do not keep resetting. If there is a burning smell, isolate and stay off. An electrician and an F-gas engineer should sort a dead supply to a split. GOV.UK certification covers the refrigerant side of that visit. A display that is dark while heating and cooling work can be booked as a non-emergency indicator fault. Do not buy a replacement display module from a sticker photo and fit it live. Do not probe connectors. Refrigerant charge does not light an LED. Leave service ports alone. If it stays dead, leave it off. Do not open covers.
Frequently asked questions
The unit cools but the numbers are dark. Is that a fault?
Often it is the display-off feature. Check the manual for a light button. If the lamps never return and you want them, an engineer can confirm whether the indicator has failed. It is not a gas fault.
Nothing at all comes on. Where do I start?
Isolator, breaker, and a wait after any power cut. One try is enough. If it stays dead, or the breaker trips, leave it off and book an electrician with an F-gas engineer. Do not open covers.
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How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.