E1 boiler fault: what it means on Baxi, Potterton and other boilers

First, read the full code

Many people search for an E1 fault because that is what they glimpse on the display, but the boiler is almost always telling them more. On most Baxi and Potterton models the code shows as a three-digit number after the E. On some displays the digits alternate or scroll, and on others the E1 appears next to a flashing symbol such as a radiator or tap.

Stand in front of the boiler for half a minute and write down everything the display shows, including any symbols. Take a photo if you can. Then find the make and model on the front panel or the data badge, usually inside the lower flap. The same code can mean different things on different makes, so the model matters.

If your boiler is a different brand altogether, an E1 or E01 may mean something unrelated. Check the user guide that came with the boiler or the manufacturer's website before acting on any of the meanings below.

Common E1xx codes on Baxi and Potterton boilers

These are the codes homeowners most often see in this family. The exact wording varies between models, so treat this as a guide to what the code is about, not a diagnosis.

If the code points to pressure

Low pressure is the most common reason for an E1 code, and the one you can usually deal with yourself. Look at the gauge on the front of the boiler with the heating off and the system cool. Most sealed systems sit at around 1 to 1.5 bar cold, but your user guide gives the right figure for your model.

If it is below that, top it up with the filling loop following your manual, close the valves again fully and reset the boiler. The real question is why it dropped. A system that needs topping up more than once or twice a year has a leak somewhere, or a problem with the expansion vessel or pressure relief valve. Our guide to a boiler losing pressure explains how to narrow that down.

If the gauge reads normal but the boiler still shows a pressure code, the sensor or switch that reports pressure to the boiler may have failed. That is an internal repair for an engineer.

If the code points to gas or ignition

E133 is the other code people see often, particularly after a power cut, in cold weather or when a prepayment meter runs out. Try the hob. If it will not light either, the problem is the gas supply: check the meter credit and that the emergency control valve by the meter is turned on, in line with the pipe.

In freezing weather, check the plastic condensate pipe outside. When it freezes, water backs up into the boiler and it will refuse to fire. Thaw it with warm, not boiling, water and reset once. Our guide to a frozen condensate pipe shows what to look for.

If gas is reaching the house and the pipe is clear, the fault is usually the ignition electrode, gas valve, gas pressure or flue. Our separate guide to the Baxi E133 fault goes into that code in more detail, and the one on a boiler not firing up covers ignition lockouts across all makes.

If you smell gas, do not reset the boiler or use any switches. Open windows, turn the gas off at the meter if safe, leave the property and call the National Gas Emergency Service on 0800 111 999.

If the code points to overheating or circulation

E110 and E125 both mean heat is not being carried away from the boiler as it should be. Check that radiator valves are open and that you have not just turned every TRV right down at once. After a system has been drained, or if the radiators are cold at the bottom, sludge or air can also restrict flow.

The usual underlying causes are a failing circulating pump, a stuck diverter valve, a blocked plate heat exchanger or a system full of sludge. None of these can be fixed by resetting. A boiler that overheats repeatedly should be left off until it has been looked at, because the safety thermostat is doing its job and something is making it trip.

Reset once, then leave it

Once you have checked the pressure, the gas and the condensate pipe, one reset following the manufacturer's instructions is reasonable. On most Baxi models it is a reset button or a combination of buttons described in the user guide. Our guide on how to reset a boiler shows the usual layouts.

If the same code comes back, stop. Repeated resets do not fix an internal fault, and on ignition codes each attempt releases a small amount of unburnt gas. Note the code, the time and what the boiler was doing, and book an engineer. Boiler lockout keeps returning explains why a repeating code is worth a proper diagnosis.

Do not take the casing off the boiler. Everything behind the front panel is gas work and must be done by a Gas Safe registered engineer.

Getting an E1 fault fixed

Loyal Plumbers covers London and everywhere inside the M25, 24 hours a day, with 10 vans on the road. Gas work is carried out by Gas Safe registered engineers. When you call 020 4652 8585, tell us the full code, the boiler make and model, the pressure reading and whether your hob works. That lets the engineer bring the parts most likely to be needed.

Our call-out charge is £60, and the engineer will explain what they have found and what the repair involves before any work starts. If your boiler is older and keeps throwing different codes, our guide on whether to repair or replace a boiler helps you weigh it up once you have a diagnosis. You can read more about the work on our boiler repair and servicing page.