Biasi ER01 Fault Code: Ignition Lockout Explained
The ER01 code appears when your Biasi boiler has attempted to ignite and failed, triggering an automatic safety lockout. The boiler shuts itself down deliberately to prevent unburned gas from building up in the combustion chamber. You will typically see the code displayed alongside a red lockout light on the front panel. Until the underlying cause is identified and resolved, the boiler will not restart on its own.
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.
What does the Biasi ER01 fault code mean?
The ER01 code appears when your Biasi boiler has attempted to ignite and failed, triggering an automatic safety lockout. The boiler shuts itself down deliberately to prevent unburned gas from building up in the combustion chamber. You will typically see the code displayed alongside a red lockout light on the front panel. Until the underlying cause is identified and resolved, the boiler will not restart on its own.
Common causes
- Insufficient gas supply or pressure Common
If the gas pressure reaching the boiler falls below the level needed for reliable ignition, the boiler cannot establish a stable flame. This could be due to the gas meter isolation valve being partially closed, a supply interruption from the network, or low mains gas pressure in your area.
- Frozen or blocked condensate pipe Common
During cold spells, the condensate pipe that carries acidic wastewater away from the boiler can freeze solid, particularly where it runs outside. The resulting blockage can prevent the boiler from operating and trigger a lockout code. This is especially common in winter and is usually straightforward to resolve yourself.
- Faulty or sticking gas valve Sometimes
The gas valve controls the flow of gas into the burner. If it sticks, fails to open fully, or has damaged wiring preventing it from communicating properly with the PCB, the boiler receives no fuel to ignite. A Gas Safe engineer will test the valve and, in most cases, recommend replacement over repair.
- Fan fault Sometimes
The boiler's fan must reach the correct speed and send a confirmation signal to the PCB before ignition is permitted. If the fan is failing, running slowly, or its wiring is damaged, the PCB will not allow the ignition sequence to proceed, resulting in a lockout.
- Blocked or partially obstructed flue Sometimes
The flue must allow combustion gases to exit safely. A bird's nest, debris, or a damaged terminal can restrict airflow enough to prevent ignition or cause the flame to fail immediately after lighting. An engineer can inspect and clear the flue.
- Dirty or damaged burner Rare
Accumulated debris on the burner jets can disrupt the gas-air mixture needed for reliable ignition. In more serious cases, the burner itself may be cracked or corroded. An engineer can clean the burner during a service or advise on replacement if it is beyond cleaning.
- PCB fault Rare
The printed circuit board coordinates the entire ignition sequence. If it is sending incorrect signals, failing to energise the igniter, or misreading sensor inputs, ignition will fail repeatedly. PCB faults are relatively uncommon but are more likely on older boilers.
How to fix it
- Check your gas supply is on DIY safe
Confirm that the isolation valve on your gas meter is fully open (handle parallel to the pipe). If other gas appliances such as your hob or gas fire are also not working, there may be a network outage — contact your gas supplier or check National Gas on 0800 111 999.
- Inspect the condensate pipe for freezing (winter months) DIY safe
Locate the condensate pipe — it is usually a white plastic pipe (32 mm or 22 mm diameter) running from the boiler to an outside drain or gulley. If it feels solid or the outer section is iced up, gently pour warm (not boiling) water along the pipe until it flows freely. Do not use a naked flame.
- Reset the boiler — once or twice only DIY safe
Press and hold the reset button on the front panel for around five to ten seconds until the display changes and the boiler begins its start-up sequence. Allow up to ten minutes for the ignition cycle to complete. If the boiler locks out again immediately, do not reset it a third time — repeated resets can allow unburned gas to accumulate in the combustion chamber.
- Check system pressure is within range DIY safe
Look at the pressure gauge on the boiler — it should read between 1.0 and 1.5 bar when the system is cold. If it is below 0.8 bar, top up via the filling loop and reset. Note that very low pressure alone is unlikely to cause ER01, but it can contribute to ignition problems.
- Call a Gas Safe registered engineer Gas Safe engineer
If the boiler locks out again after a reset or two, stop resetting and arrange for a Gas Safe registered engineer to attend. They will carry out a gas pressure test, inspect the gas valve, fan, flue, and burner, and use diagnostic equipment to pinpoint the exact cause. Do not attempt to open any gas-carrying components yourself.
Parts you may need
- Gas valve · from £120
- Boiler fan (flue fan assembly) · from £95
- Burner assembly · from £110
- Ignition electrode · from £25
- PCB (printed circuit board) · from £180
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 £120–£380, depending on the underlying cause.
Frequently asked questions
Is it safe to keep resetting my Biasi boiler when ER01 appears?
No. You can try one or two resets to see whether a one-off glitch has cleared, but repeatedly resetting an ER01 lockout is not safe. Each failed ignition attempt can introduce unburned gas into the combustion chamber. If the boiler locks out again after a couple of resets, leave it off and call a Gas Safe registered engineer to find the root cause.
Could a frozen condensate pipe cause ER01?
Yes, and it is one of the most common reasons for this code during cold weather. When the condensate pipe freezes, the boiler cannot dispose of waste properly and shuts down. You can thaw the pipe yourself using warm water poured carefully along the outside section. Once it is flowing freely, reset the boiler. If the fault returns or the weather stays cold, consider lagging the pipe to prevent a repeat freeze.
How much does it cost to fix a Biasi ER01 fault in the UK?
Most homeowners pay between £120 and £380, depending on what the engineer finds. A straightforward gas pressure adjustment or ignition electrode replacement sits at the lower end. A gas valve or fan replacement typically costs £250–£380 including labour. A PCB replacement can push costs higher — sometimes £400 or more — and on an older boiler it may be worth comparing that against the cost of a new boiler installation.
My Biasi boiler shows E133 rather than ER01 — is it the same problem?
Yes. Newer Biasi models such as the Inovia and Advance Plus display the same ignition lockout fault as E133, while older ranges like the Riva Plus and Garda use ER01. The causes, diagnostic process, and repair options are identical regardless of which code appears on your display.