Overview
E430 on a Potterton Assure combi or system boiler, and especially E430 + "flame crossed", is reported by Potterton as a water pressure test failure. Practically this means the boiler has performed an internal check related to primary system pressure and either detected that the pressure is outside expected limits during that test or the test circuitry/sensor has not passed. The additional "flame crossed" indication (or flame symbol with a cross) is Potterton’s way of showing the boiler has gone into a protective lockout related to that test — the burner will not run until the fault is cleared and the system is proven safe. Why it happens: the most common causes are low system pressure (loss of water from the sealed heating system), a failed pressure sensor/switch, a fault in the flow/pressure test circuitry on the PCB, or an intermittent condition such as a leak, air in the system or a stuck flow switch/pump. Severity and action: this is a safety-related lockout (the boiler is preventing operation when it detects an unsafe condition). If the cause is simply low pressure, a competent homeowner can check and top up pressure; however, anything involving gas, the burner, internal sensors, wiring or persistent faults must be handled by a Gas Safe registered engineer. Do not attempt to access internal gas components or PCB electronics yourself.
Possible Cause: Water pressure test failed
Troubleshooting Steps
Safety precautions:
1) If you smell gas, leave the property immediately and call the gas emergency service. Do not operate electrical switches or the boiler.
2) Before doing any checks, switch the boiler to standby/off at the mains switch and isolate power if you will be touching plumbing connections. Only perform simple pressure checks/visual inspections if you are comfortable and confident.
3) Do not remove the boiler casing, touch gas pipes, the gas valve, burner, or PCB. Any internal electrical or gas work requires a Gas Safe engineer.
Initial homeowner checks (what you can safely do):
1) Note the exact error code and any lights/indicators. Take a photo of the display for the engineer.
2) Check the system pressure gauge on the front of the boiler. Normal cold pressure is typically about 1.0–1.5 bar for most domestic combi systems. If it is below ~1.0 bar, that is likely the immediate trigger.
3) Visually inspect for obvious leaks from pipework, radiators, valves, or under the boiler. Check radiators recently bled or any new damp patches.
4) Try a basic reset: switch the boiler off at the mains for 30 seconds and switch back on, then observe whether the code returns.
If the pressure is low: repressurise safely
1) Locate the filling loop (flexible hose or built-in filling valve) and ensure you know how your boiler model requires operation. The filling loop must be closed/capped after use.
2) Open the filling loop slowly until the pressure rises to about 1.2–1.5 bar (check your boiler manual for the exact recommended value). Watch the pressure gauge while filling. Close the filling loop fully and ensure any isolation valves are secured.
3) Reset the boiler following the manufacturer procedure and see if the E430 clears. If the code clears and the boiler runs normally, monitor the pressure over the next days.
4) If pressure drops again after repressurising, there is a leak or a failing component (not a permanent DIY fix) — call an engineer.
If the pressure was normal or topping up does not clear the fault:
1) After a reset, if E430 + flame crossed returns, the problem may be a faulty pressure sensor, flow switch, pump not circulating correctly, airlock, or an electrical/PCB issue. Note any other codes or symptoms (pump noise, no circulation, false flame warnings).
2) Bleed radiators to remove airlocks (only if you know how). Low or trapped air can affect circulation and pressure behaviour. Repressurise afterwards if required.
3) Listen when the boiler attempts to operate: does the pump run? Any unusual noises? No pump movement or repeated failed ignition combined with the code is important info for the engineer.
4) Check that the filling loop is fully closed and not leaking. Also check external mains gas supply by confirming other gas appliances are working (but do not attempt more than a visual check).
When to call a professional (and what to tell them):
1) Call a Gas Safe registered heating engineer if the fault persists after you have checked/reset and repressurised, if the boiler repeatedly loses pressure, if you find a leak, or if the E430 returns with the flame crossed indicator. Also call an engineer for any electrical or component fault, or if other error codes appear.
2) When you call, give them the exact model and the error code (E430 and the flame-crossed symbol), describe the system pressure reading, steps you tried (reset/repressurise/bleed radiators), and whether pressure drops were observed. Send the photo you took of the display if possible.
3) The engineer will typically test pressure sensor/switch operation, check the filling loop and system for leaks, verify pump and flow-switch operation, inspect sensor wiring and PCB behaviour, and run safe ignition/flame detection tests. They can replace defective sensors, repair leaks, or replace parts as required.
Final notes:
1) Do not attempt internal repairs on the gas or electrical components of the boiler. That work must be done by a Gas Safe engineer. Re-pressurising, resetting, visual leak checks and bleeding radiators are the limit of safe DIY actions.
2) Keep records of fault occurrences, pressure readings and any maintenance you perform — this helps the engineer diagnose intermittent issues quickly.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Potterton Assure Combi and system.