It is a cold morning. You turn on the shower and the water stays cold. You check the boiler display. There is a code. You do not know what it means. You call the engineer. He charges $120 to come out, resets the pressure, and leaves in eight minutes.
Here is what you can do yourself before that call.
The two most common causes
Low pressure
Most modern boilers require a water pressure between 1 and 1.5 bar. When pressure drops below 1 bar, the boiler locks out for safety. You will see a low pressure indicator or a specific error code (common codes: F1, E1, EA on different brands).
Check the pressure gauge on the boiler — it is usually a small dial or a digital reading on the display. If it is below 1 bar, you need to repressurise the system.
How to repressurise: Find the filling loop — a small flexible hose connecting two pipes under the boiler. Open both valves slowly until the gauge reads 1.2 to 1.5 bar. Close both valves. Press the reset button on the boiler.
The reset
Many boiler lockouts are temporary faults that clear with a reset. Find the reset button — usually marked with an arrow or the word Reset, sometimes behind a flap on the front panel. Hold it for 3 to 5 seconds. The boiler will attempt to restart.
If it fires up and the error clears: done. If the error returns within an hour, the underlying cause needs investigation — that is the point to call an engineer.
What the error codes typically mean
Error codes vary by brand, but most fall into a few categories: pressure issues (F1, E118, A1), ignition failures (E2, F4), sensor faults (E3, E5), or overheating (F3, E10). Your boiler manual — usually found by searching your boiler model online — will list what each code means for your specific unit.
When to call an engineer
Call an engineer if the error involves gas supply, a carbon monoxide warning light, a burning smell, visible corrosion or water leaks around the boiler, or an error that returns immediately after a reset. These are not DIY situations.
Everything else is worth checking yourself first. The engineer's job is not to know more than you — it is to have more tools. Start with what you can do before they arrive.
This repair is one of eight covered in She Fixed It, with step-by-step instructions and photos for the repressurise and reset process.