Seeing an E1 error code on your boiler can be worrying, but in most cases it’s something relatively straightforward. On many modern boilers, an E1 fault usually means the system pressure is too low, and the boiler has stopped running to protect itself.
Some boiler manufacturers also use E1 as a general fault category, which means the numbers that follow it are important. For example, E119 often means low pressure, while E133 usually relates to ignition problems.
So the first thing to do is check the full error code on the display or in your boiler manual.
What an E1 Error Code Usually Means
In most UK heating systems, boilers need enough water pressure to circulate heat properly through radiators and pipework. If the pressure drops too low — usually below around 1 bar — the boiler will lock out.
This safety feature prevents damage to components like the pump, heat exchanger, and sensors.
In simple terms, low pressure stops the boiler working safely, so it shuts down until the pressure is restored.
Some common E1-related codes you might see include:
- E119 — low system pressure
- E133 — ignition lockout or gas supply issue
- E110 — overheating fault
Different boiler brands use slightly different coding systems, so checking the manual always helps.
Common Causes of an E1 Boiler Fault
Low pressure is by far the most common reason for an E1 error.
This can happen if radiators have recently been bled without topping the system back up, or if there’s a small leak somewhere in the heating system. Over time, even tiny leaks from radiator valves, pipe joints, or the pressure relief valve can cause pressure to fall.
During very cold weather, a frozen condensate pipe can also stop the boiler operating correctly and trigger fault codes.
In some cases, the issue may be inside the boiler itself, such as a faulty pressure sensor, temperature probe, or PCB, though this is less common than simple pressure loss.
On certain models, E1-series faults can also relate to gas supply or ignition problems, which will usually show with additional numbers in the error code.
How to Fix an E1 Error (Low Pressure)
If the error is caused by low pressure, it’s often something you can safely fix yourself.
First, check the pressure gauge on the boiler. When the system is cold, it should normally sit between 1.0 and 1.5 bar. If it’s below that, the boiler may display an E1 fault.
You can usually restore pressure using the filling loop, which is often a small silver braided hose or built-in lever underneath the boiler. Open the valves slowly and watch the pressure rise to around 1–1.5 bar, then close them firmly.
After that, reset the boiler using the reset button or dial setting recommended in the manual.
If low pressure was the cause, the boiler should start working again.
Check for Leaks if Pressure Drops Again
If you need to top the pressure up regularly, there’s probably an underlying issue. Look around radiators, pipework, and beneath the boiler for damp patches, drips, or corrosion marks.
A system that keeps losing pressure usually means water is escaping somewhere, and that will need investigating.
When to Call an Engineer
While an E1 fault is often minor, it shouldn’t be ignored.
You should contact a Gas Safe registered engineer if the pressure keeps dropping, if the error relates to ignition or overheating, or if you notice leaks or unusual boiler noises.
Repeatedly resetting the boiler without fixing the cause can lead to bigger problems later.
At Boilers2go, we often tell customers that E1 is usually a warning sign rather than a major failure — but it’s always worth checking properly.
With years of experience in boilers and home improvements in general, Myles Robinson is a passionate advocate for making home heating simpler, safer, and more affordable for households across the UK. With years of experience in the heating industry, Myles combines hands-on knowledge with a focus on customer-first service, helping homeowners choose the right boiler, understand their systems, and keep their heating running efficiently all year round. His articles break down complex topics into clear, practical advice you can trust.