Overview
E430 on a Baxi 600 combi typically indicates a temporary water pressure related fault — the boiler has detected a pressure condition outside of its expected range or a brief pressure fluctuation during a self-test. On many Baxi models these issues are often temporary and clear after a reset if the underlying cause was a short-lived event such as a momentary drop in system pressure, a sensor glitch, or the condensate pipe freezing and temporarily affecting operation. The code is a protective response to prevent damage from running with incorrect pressure or without correct circulation. Severity depends on whether the fault is transient or persistent. If the E430 appears once and clears after a reset and the boiler then operates normally, it is low severity. If the code returns, the boiler will likely lock out and will need further investigation because repeated pressure faults can cause dry-fire damage, pump strain or indicate leaks, a failed pressure sensor, a faulty filling loop or a circulation issue. If the fault persists, or if you smell gas, see leaks, or have no heating or hot water, you should contact a Gas Safe registered engineer rather than continuing DIY attempts.
Possible Cause: Water pressure temporary test.
Troubleshooting Steps
Safety precautions:
1) If you smell gas, do not touch the boiler controls. Open windows, leave the property and call the national gas emergency number immediately. 2) If there is a significant water leak, isolate the mains water to the property and the boiler’s isolation valves, and switch off electricity to the boiler. 3) Do not repeatedly reset the boiler more than once or twice; repeated resets can mask a real fault and cause further damage. 4) Only carry out simple checks and tasks you are comfortable with; anything involving gas, the burner, or internal components must be done by a Gas Safe engineer.
Initial checks a homeowner can do:
1) Look at the pressure gauge on the front of the boiler when the system is cold. Aim for roughly 1.0–1.5 bar when cold (follow your boiler manual for the exact target for your model). 2) Check for any visible water leaks around the boiler, pipework, radiators and the pressure relief discharge pipe (often a copper pipe that may drip if PRV has opened). 3) Check radiators for cold spots and listen for unusual noises (gurgling) which can indicate trapped air or poor circulation. 4) If it is freezing outside, check the condensate pipe (usually a plastic pipe running to outside waste) for ice blockage. 5) Confirm the gas supply is on and other gas appliances are working if you suspect ignition issues.
Specific diagnostic and fix steps:
1) If the pressure is low (below about 1.0 bar):
a) Locate the filling loop (a braided hose or valve assembly under the boiler). Ensure the boiler power is on so you can watch the gauge while topping up.
b) With both filling loop valves closed, open one valve slowly then the other until the gauge rises to around 1.2–1.5 bar. Close both valves firmly once the correct pressure is reached. Some systems have a removable filling loop; if so, remove it or ensure it is fully closed after use.
c) Bleed radiators to remove air pockets: turn heating off, let radiators cool, use a radiator key to open bleed valves until water appears, then close. Re-check pressure and top up again if required.
d) Reset the boiler following the manufacturer’s guidance (press and hold the reset button or use the selector switch marked R for about 5–10 seconds). Only attempt one reset after corrections.
2) If the pressure is too high (needle in red zone):
a) Turn off the boiler and allow the system to cool.
b) Bleed one or more radiators to release water until the gauge falls to the correct range. Alternatively use the system drain point if you know its location and operation.
c) Check that the filling loop valves are fully closed so the system is not being continuously overfilled.
3) If the condensate pipe is frozen (common in cold weather):
a) Turn the boiler off at the control panel and the electricity at the wall.
b) Locate the external condensate pipe and gently thaw it with warm (not boiling) water, a hot water bottle or by wrapping with a thermal blanket. Do not use open flames.
c) Once thawed, restore power and reset the boiler.
4) If there are no visible leaks, pressure remains unstable, or the E430/pressure fault returns after resetting:
a) Do not keep attempting resets.
b) Note any additional symptoms or error codes, whether the pressure steadily falls or rises, and whether hot water or heating is affected.
c) Call a Gas Safe registered engineer. Mention the E430 code and your observations (pressure readings, leaks, frozen condensate, repeated lockouts).
When to call a professional:
1) If the fault persists after topping up, bleeding radiators and a single reset. 2) If you find a leak, cannot stop pressure loss, or the boiler repeatedly locks out. 3) If you suspect a faulty pressure sensor, pump fault, filling loop problem or internal electrical/PCB issue. 4) If you smell gas or see signs of burner/ignition problems. A qualified Gas Safe engineer should carry out repairs involving gas, internal components, pressure sensor replacement, pump replacement, PRV replacement or any work on the heat exchanger.
Final note: E430 can be a temporary pressure-related alert that clears after a simple homeowner check and reset, but repeated occurrences or associated faults require a professional inspection to ensure the boiler and central heating system are safe and reliable.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi 600 Combi Gas Boiler.