Overview
Error 164 on a Baxi EcoBlue boiler normally indicates a pressure sensor fault (UK) or a heating flow switch error (Ireland). In practice this means the boiler’s control electronics are not getting a valid signal about water pressure or flow in the primary heating circuit. That can be caused by a failed or disconnected sensor, an intermittent wiring/connector fault, very low or very high system pressure, poor circulation (pump failure or airlock) or, less commonly, a PCB or safety-thermostat response to an overheat condition. Severity ranges from low to high depending on cause. If it’s simply low pressure or air in the system you can often resolve it yourself and the fault will clear after repressurising, bleeding radiators and a reset. If the code remains, or if it appears with signs of overheating, repeated lockouts, or you detect a gas smell or electrical faults, it becomes a safety issue and requires a Gas Safe (UK) or appropriately qualified technician (Ireland). Replacing sensors, diagnosing pump faults, checking PCB communications or any work involving gas or internal electrics should be left to a professional.
Possible Cause: Pressure Sensor Error (UK) – Heating flow switch error (Ireland)
Troubleshooting Steps
Safety precautions:
- If you smell gas, evacuate the property immediately, do not operate electrical switches, and call the gas emergency number for your area.
- Turn off the boiler and isolate electrical supply at the fused isolation switch before removing any covers. If you are not qualified to work on gas appliances or internal electrics, do not open the boiler.
- Allow the boiler to cool before touching pipework. Beware of hot surfaces and moving pump parts.
Initial checks a homeowner can do:
1. Note exactly when the 164 code appears and whether the boiler is locked out. Try a single reset (see reset step below) and record if the code returns immediately or after a period of running.
2. Check the pressure gauge on the boiler: normal resting pressure is commonly around 1.0–1.5 bar (some guidance allows up to 2.0 bar). If pressure is below about 0.5 bar the boiler may register a pressure/dry-fire fault.
3. Look for obvious leaks around the boiler, radiators and pipework. A system losing water will drop pressure and trigger sensor errors.
4. Check radiators for cold spots and listen for the pump. Lack of circulation (pump not running or airlocked) can cause sensor/flow faults.
5. Inspect external flue and condensate pipe for obvious blockages or freezing which can cause other errors—clear if safe to do so.
Specific diagnostic and fix steps homeowners can try:
1. Re-pressurise the system if pressure is low: locate the filling loop (flexible braided hose or built-in loop with two isolation valves). With the boiler off, open the loop valves slowly while watching the pressure gauge until it reaches about 1.0–1.5 bar, then close both valves. Ensure the filling loop is secured/removed if it is a temporary hose. If pressure drops again soon after, there is a leak and you should call a professional.
2. Bleed radiators to remove trapped air: start with the highest radiator in the house, use a radiator key to release air until water flows, then re-check boiler pressure and top up if needed.
3. Reset the boiler once pressure and circulation checks are done: follow your model’s reset procedure (usually a reset button or selector marked R; hold for 5–10 seconds). Do not keep repeatedly resetting if the fault returns immediately.
4. Check for pump operation: with the boiler running (and after isolating electrics if you need to inspect), listen for the pump running or feel the pump casing carefully (don’t touch moving parts). If the pump is silent and you have confirmed power to the boiler, do not attempt internal repairs — call an engineer.
5. Check visible wiring and connectors only if competent: with power isolated, look for loose connectors on sensor leads that are reachable without removing the boiler cover. Do not probe internal PCB connections or gas components unless qualified.
When to call a professional:
- If the 164 code persists after repressurising, bleeding and a reset.
- If the boiler displays overheating symptoms, repeated lockouts, or the pressure drops repeatedly.
- If you detect electrical faults, burnt smells, or if replacing or testing sensors, pump or PCB communications is required.
- If you are not confident isolating/working on the filling loop or any boiler internals.
What the engineer will likely check and do:
- Use diagnostic equipment to read live sensor values and confirm whether the pressure transducer / flow switch is faulty, disconnected or being given incorrect readings.
- Inspect and test the pump for operation, remove airlocks if necessary, and check circulation rates.
- Check for leaks, replace faulty pressure sensors or flow switches, and test wiring and PCB communications. They will also check flue temperatures and safety thermostat operation if overheating is suspected.
Final notes:
- Do not continue to operate the boiler if the fault returns repeatedly or if there are signs of overheating, gas smell or electrical issues.
- Temporary fixes such as frequent resets can mask a developing fault and should be avoided. Call a Gas Safe registered engineer (UK) or appropriate qualified heating engineer (Ireland) if the problem is not cleared by the basic checks above.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi EcoBlue.