Overview
E154 on Potterton Promax/Ultra/Gold/Titanium boilers indicates a primary flow fault — essentially the boiler has detected a problem with the primary heating flow circuit. On most Potterton lists this is described as a flow/return temperature mismatch or a failed flow/return sensor test. In practice the fault is raised when the boiler cannot confirm correct circulation or when the flow sensor/thermistor that monitors the primary flow temperature is reading incorrectly compared with the return, or when the pump/pipework is not moving water as expected. Severity ranges from moderate to high: the boiler will often reduce operation or lock out to protect itself (and to prevent overheating) if it detects poor flow. Sometimes the cause is a simple loss of circulation (airlock, closed valves, low pressure) that a homeowner can fix; other times it is a failed sensor, pump fault, blocked heat exchanger or wiring/PCB issue that requires a qualified Gas Safe engineer. Any diagnosis or repair that involves the gas supply, burner, internal wiring, PCB, or dismantling the boiler should be left to a professional for safety and warranty reasons.
Possible Cause: Primary flow fault
Troubleshooting Steps
Safety first
- If the boiler is showing other warnings (excessive heat, leak, visible damage) switch the boiler off, isolate electrical supply at the fused spur and turn off the gas at the isolator if you can do so safely. Do not attempt internal repairs.
- Never remove sealed covers, the burner assembly, or attempt electrical/gas repairs unless you are a Gas Safe registered engineer.
Initial homeowner checks (safe, straightforward steps)
1. Reset the boiler once: use the boiler reset button following the manual. Note whether E154 returns immediately or after a short run.
2. Check system pressure on the pressure gauge. If it is below about 1.0–1.2 bar repressurise to the normal working pressure (typically ~1.2 bar) following the boiler manual. If pressure is extremely low or keeps dropping, do not keep running the boiler.
3. Turn CH demand on (set room stat/thermostat high) and listen at the boiler for the pump running (a low hum or vibration). Walk round the radiators — are any getting warm, starting at the nearest ones?
4. Bleed one or two radiators (starting with the highest/radiator nearest the boiler) to remove air and then recheck system pressure and circulation.
5. Check that any external zone valves and TRVs are open and that radiator valves are turned up.
6. Check visible pipework and connections for leaks and check the condensate pipe (in cold weather) is not frozen or blocked.
Specific diagnostic and fix steps (when to proceed and what they involve)
1. If reset cleared the error and normal operation returned, monitor pressure and performance. If E154 returns, proceed with checks below.
2. If the pump appears not to run but you hear no hum, this suggests pump failure, blocked pump or electrical supply to pump. Confirm the pump isolation valves (on either side of the pump) are open. If valves are closed do not force them; call an engineer.
3. Check for circulation by feeling the flow and return pipes (careful: they may be hot). The flow pipe should be significantly hotter than the return when the boiler is running. If both are nearly the same temperature the pump may not be circulating.
4. If you have bled radiators and repressurised but still have no circulation, there may be an airlock in the system — a small engineer-led pump purge or use of the pump’s manual overrun may be needed.
5. Inspect visible sensor wiring and connectors (on the outside of the boiler or to accessible sensors) for loose connections or corrosion. Do not disconnect sealed internal connectors; only check external plug-in leads if accessible and safe to do so.
6. If wiring and visible connections look OK and circulation issues persist, the likely causes are: faulty flow thermistor (NTC), faulty return thermistor, failed pump, blocked heat exchanger/strainer, stuck diverter/zone valve, or PCB fault. These require tools and tests (NTC resistance checks, voltages, pump amp draw and rotation checks, pressure differential measurements and possibly a system flush) and should be done by a Gas Safe engineer.
7. If the boiler displays additional codes like E110 (overheat) or E125/E109 (circulation faults), switch the boiler off and contact an engineer as these point to pump jammed, safety thermostat tripped or blocked flow that can cause damage if run.
When to call a professional
- Call a Gas Safe registered heating engineer if E154 persists after basic checks (reset, repressurise, bleed radiators, confirm valves open).
- Also call a pro if you suspect pump failure, if you find damaged wiring, if the fault coincides with overheat lockout, or if you are not comfortable performing the safe checks described. The engineer will test thermistor resistances, check pump operation and rotation, inspect and clean strainers/heat exchanger, check wiring to the PCB and replace the flow sensor, pump or PCB as required.
Final note
- Do not attempt gas or electrical repairs yourself. Use the boiler manual for safe reset and repressurisation instructions. Persistent E154 faults need a qualified engineer to diagnose and repair safely.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Potterton Promax Ultra, Gold/Titanium Combi & System.