Baxi E1 Fault Code: Causes, Fixes & Repair Costs
What does the Baxi E1 fault code mean?
The E1 code on Baxi, Potterton, and Main boilers signals that the sealed central heating circuit has dropped below its safe operating pressure, causing the boiler to lock out and suspend both heating and hot water. On older or simpler models, E1 appears on its own as a straightforward low-pressure alert. However, on the HE A Range (including the Combi Platinum, Combi Duo-tec, System Megaflow, and Heat Only Sola), the display alternates between "E" or "E1" and a two- or three-digit number — so the full code you see might be E119, E133, E168, E110, or E118. Each of these points to a distinct underlying fault: E119 and E118 both confirm water pressure has fallen (E118 specifically below 0.5 bar); E133 indicates a gas supply or ignition problem, sometimes caused by a frozen condensate pipe; E110 means the boiler has shut down due to overheating; and E168 is a general internal safety shutdown. Identifying which sub-code is showing will guide the correct fix.
General guidance only — not a substitute for professional advice. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Low system pressure (slow leak or natural loss) Common
The most frequent trigger for E1, E119, and E118. Sealed systems lose small amounts of water gradually through microscopic joint weeps, valve packings, or after radiators are bled. Once pressure drops below roughly 0.5–1.0 bar, the boiler's pressure sensor trips the lockout. Check the pressure gauge — a reading below 1 bar confirms this is the likely cause.
- Faulty or weeping pressure relief valve Common
The pressure relief valve (PRV) is designed to open and discharge water if pressure rises too high. If the valve seat is worn or the spring is weakened, it can allow water to seep out slowly even at normal pressures, causing a gradual but persistent pressure drop. A telltale sign is a damp or dripping overflow pipe outside the property.
- Frozen or blocked condensate pipe (E133) Common
In cold weather, the condensate pipe — the plastic pipe that carries waste water from the boiler to a drain — can freeze solid. This blocks the boiler's ability to expel flue gases safely and triggers the E133 sub-code. Thawing the pipe is a homeowner-safe task and often resolves the lockout immediately.
- Faulty water pressure sensor Sometimes
The pressure sensor tells the boiler's PCB what the circuit pressure is. If the sensor drifts or fails, it can report a falsely low reading and trigger E1 or E119 even when actual pressure is within range. Suspect this if repressurising brings the gauge to 1.5 bar but the fault code immediately returns.
- Waterlogged or failed expansion vessel Sometimes
The expansion vessel absorbs pressure increases as water heats up. If its internal diaphragm splits or the pre-charge pressure is lost, system pressure can swing erratically — dropping when the boiler is cold and spiking dangerously when hot. This can cause repeated E1 lockouts that repressurisation only temporarily fixes.
- Gas supply interruption (E133) Sometimes
If the gas meter valve is closed, the gas supply has been interrupted by the network, or there is a fault in the internal gas valve, the boiler will fail to ignite and display E133. Check that other gas appliances in the property are working before assuming the boiler is at fault.
- Overheating or blocked heat exchanger (E110) Rare
The E110 sub-code appears when the primary water temperature exceeds safe limits. This can result from a sluggish pump, a partially blocked heat exchanger due to sludge build-up, or a faulty thermistor. The boiler shuts down to prevent damage and must be assessed by an engineer if a single reset does not clear it.
- Internal electrical or PCB fault (E168) Rare
E168 is triggered when the boiler's control board detects an unspecified internal fault severe enough to warrant a full safety shutdown. It can be caused by a PCB fault, a wiring issue, or a failing component sending unexpected signals. This code always requires a Gas Safe engineer to diagnose.
How to fix it
- Check the pressure gauge DIY safe
Locate the pressure gauge on the front panel or underneath the boiler. A reading below 1 bar — or below 0.5 bar for E118 — confirms low pressure is the root cause. If the gauge reads 1–2 bar and the code is E133, E110, or E168, skip to the relevant step below.
- Top up system pressure via the filling loop DIY safe
Find the filling loop — usually a braided flexible hose with two inline valves, located beneath the boiler. Ensure both valves are closed first. Slowly open one valve fully, then gently crack open the second, watching the pressure gauge rise. Stop at 1.5 bar, then close both valves firmly. Never exceed 2 bar.
- Reset the boiler DIY safe
Press and hold the reset button (usually marked with a flame or a circular arrow symbol) for around three seconds. Allow the boiler two to three minutes to restart and run through its ignition sequence. If the fault clears and the boiler fires, monitor the pressure over the next few days to check it holds.
- Bleed radiators if pressure keeps dropping DIY safe
Trapped air in the system can cause uneven heating and contribute to pressure fluctuations. Turn the heating off and let it cool. Using a radiator bleed key, open each radiator's bleed valve (usually at the top corner) until water — not air — trickles out, then close it. You may need to top up the system pressure again afterwards.
- Thaw a frozen condensate pipe if E133 appears in cold weather DIY safe
Locate the condensate pipe — the white or grey plastic pipe (typically 21.5 mm or 32 mm diameter) that runs from the boiler to an external drain or gulley. Pour warm (not boiling) water over the frozen section, or apply a heat pad or hot water bottle. Once thawed, reset the boiler. Never use a naked flame.
- Check the gas supply is active DIY safe
If the display shows E133 and the weather is mild (so a frozen condensate pipe is unlikely), check that other gas appliances such as the hob or gas fire are working. If they are not, contact your gas supplier or call the National Gas Emergency Service on 0800 111 999. Do not attempt to inspect or operate the gas valve yourself.
- Call a Gas Safe registered engineer if the fault persists or returns Gas Safe engineer
If pressure drops again within a few days of repressurisation, if E110, E133, E168, or E119 return after a reset, or if you cannot identify the cause, a Gas Safe registered engineer must inspect the system. They can locate hidden leaks, test the expansion vessel pre-charge, replace the PRV or pressure sensor, assess the heat exchanger for sludge, and diagnose PCB or electrical faults safely and legally.
Parts you may need
- Water pressure sensor · from £35
- Pressure relief valve (PRV) · from £25
- Expansion vessel (replacement) · from £55
- Filling loop assembly · from £20
- Condensate trap · from £18
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £100–£350, depending on the underlying cause.
Frequently asked questions
Can I re-pressurise my Baxi boiler myself to clear the E1 code?
Yes — topping up the system pressure via the filling loop is a homeowner-safe task and is often all that is needed to clear a standalone E1 or E119 code. Bring the gauge up to 1.5 bar, close both filling loop valves securely, then reset the boiler. If the pressure drops again within a short time, there is likely a leak or a failed expansion vessel that needs a Gas Safe engineer to fix.
What is the difference between E1, E118, and E119 on a Baxi boiler?
On simpler Baxi models E1 appears on its own and simply means the circuit pressure is too low. On the HE A Range, the display shows a more specific sub-code: E118 means pressure has fallen below roughly 0.5 bar (a more severe drop), while E119 means pressure is low but above that critical threshold. Both are resolved the same way — by repressurising the system — but E118 indicates a bigger pressure loss and makes it more important to check for an active leak.
My Baxi is showing E133 — is that the same as E1?
Not exactly. E133 is part of the E1 sub-code family on HE A Range models, but it points to a gas supply or ignition fault rather than a water pressure problem. The most common cause in winter is a frozen condensate pipe, which you can thaw yourself. If the pipe is not frozen, the issue may be with the gas supply or the internal gas valve, and you will need a Gas Safe registered engineer to investigate — do not attempt to work on gas components yourself.
How much does it cost to fix a Baxi E1 fault?
If repressurising the system clears the fault and pressure holds, the fix costs nothing. If an engineer is needed, most common repairs — such as fixing a small leak, replacing a pressure relief valve, or recharging an expansion vessel — typically fall between £100 and £350 including labour. Replacing a pressure sensor is usually at the upper end of that range. In rare cases where a heat exchanger needs replacing or significant pipework repairs are required, costs can exceed £500, but this is unusual for a pressure-related E1 fault.