Overview
E109 on a Baxi GA range boiler indicates a circulation fault — the primary heating water is not moving as it should through the boiler and system. The boiler detects inadequate flow or pre-circulation and locks out to protect itself from overheating or dry firing. Typical causes are air trapped in the system, low system pressure, closed or partially closed isolation/zone valves, a seized or blocked pump, blocked strainers or magnetic filters, or blockages/scale in the heat exchanger or pipework. Severity is moderate to high. The boiler will usually stop supplying heating (and may limit hot water) until circulation is restored. Some causes are user-fixable (bleeding radiators, repressurising the system, opening valves), but faults involving the pump, internal filters, heat exchanger blockages, or internal sensors require a qualified Gas Safe engineer. Do not attempt gas, electrical, or internal boiler repairs if you are not a trained professional.
Possible Cause: Poor circulation
Troubleshooting Steps
Safety first
- If you smell gas, leave the property immediately, do not operate electrical switches, and call the gas emergency number and a Gas Safe engineer.
- If you are unsure at any stage, stop and call a Gas Safe registered engineer. Do not work on gas or electrical components unless you are qualified.
Initial checks a homeowner can do
1) Record the exact fault code (E109) and any other messages, and note when it appeared and what you were doing (turning heating on, after a power cut, etc.).
2) Check the boiler pressure gauge. Baxi systems normally run around 1.0–1.5 bar when cold. If pressure is below about 0.8–1.0 bar top up the system using the filling loop (follow the boiler handbook). Only use the filling loop if you know how; close it when pressure is correct.
3) After topping up, try a single reset of the boiler (hold reset for the time advised in your manual). Do not repeatedly reset if the code returns.
4) Bleed radiators to release trapped air. Start with the radiator nearest the boiler, then work around the house. Re-check system pressure and re-pressurise if it falls.
5) Check room thermostats, timer/programmer and confirm the boiler is actually being called to heat. Ensure any external controls are set to demand heating.
6) Check visible pipework and radiator valves are open (including motorised zone valve indicators and any isolating valves on the boiler pump). If valves are closed, open them slowly and re-check operation.
7) Feel the flow and return pipes at the boiler when it tries to fire. If both stay cold or the flow is only lukewarm while the boiler is running, circulation is impaired.
Further diagnostic steps (if you are comfortable and safe to do so)
8) Listen for the pump when the boiler tries to run. You should hear or feel it operate briefly when the boiler attempts to heat. A silent pump or a pump that hums but does not move water can indicate a seized or electrically failed pump.
9) If you have an accessible magnetic filter or pump strainer and you are competent with isolating and draining small amounts of system water, you can check/clean the strainer. Isolate and relieve system pressure first, and be prepared for some water loss. If you are not confident, stop and call an engineer.
When to call a professional
- If pressure topping up, bleeding radiators and a single reset do not clear the code.
- If the pump does not appear to run, is noisy, or feels seized.
- If you find repeated pressure loss (possible leak) or suspected blockages/scale in the heat exchanger or pipework.
- If any other fault codes appear alongside E109.
What the engineer will do
A Gas Safe engineer will isolate and inspect the pump, check pump speed/voltage, check motorised valves and wiring, inspect strainers and magnetic filters, flush or chemically clean blockage if needed, check the heat exchanger and sensors, and test the control circuits. They will also re-pressurise and test the system under demand.
Final warnings and best practice
- Do not repeatedly reset the boiler; that can mask a real fault and cause further problems.
- Do not attempt gas or internal electrical repairs yourself. Use a Gas Safe registered engineer for any internal work or if the simple DIY checks above do not cure the fault.
- Keep a record of the fault code, what you tried, and provide that information to the engineer to speed diagnosis.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi GA Range.