Overview
The F9 fault on an Ideal boiler commonly indicates a problem with the boiler’s control electronics and/or the water flow/pressure sensing system. In many Ideal models F9 can appear when the printed circuit board (PCB) is unconfigured or the wrong boiler chip card (BCC) is fitted, but it is also used by some sources to signal water pressure/flow or sensor faults (flow thermistor, pressure sensor, pump or circulation issues). When the PCB and its associated chip card are not correctly recognised or set up the boiler will lock out as a safety measure. Severity is medium to high: the boiler will usually shut down and you will lose heating and possibly hot water until the fault is resolved. Because the fault can involve gas, live electronics, and sealed components, most repairs (PCB/chip replacement, sensor wiring or thermistor replacement, pump or heat exchanger work) should be carried out by a qualified Gas Safe registered engineer. Homeowners can safely do a limited set of checks (pressure, simple resets, bleeding radiators) but must not open or work on the PCB, gas components or internal wiring themselves.
Troubleshooting Steps
Safety precautions:
- If you smell gas or suspect a gas leak, stop, leave the property immediately and call the gas emergency number. Do not attempt any checks.
- Before touching any boiler controls, turn the boiler off and allow it to cool. For electrical isolation use the boiler fused spur or switch at the consumer unit if appropriate.
- Do not open the boiler casing, touch the PCB, or attempt electrical or gas repairs unless you are a qualified engineer. Working on gas appliances is dangerous and illegal without proper certification.
Initial checks a homeowner can do (safe, step-by-step):
1. Note the exact fault code and any accompanying lights or messages. Also note if hot water or central heating is affected.
2. Check the boiler pressure gauge when the system is cold. Normal static pressure is usually around 1.0–1.5 bar (consult your boiler manual for the exact figure). If pressure is significantly low (under about 1.0 bar) top up the system using your filling loop according to your boiler manual.
3. If you have just topped up pressure, bleed a few radiators to remove trapped air and re-check the pressure. Top up again if needed and ensure the filling loop valves are closed and secured after use.
4. Try a single reset of the boiler as per the manual or by using the reset button. If the fault persists, do not keep resetting repeatedly (repeated resets can mask faults and may trigger additional lockouts).
5. Power-cycle the boiler by switching off at the fused spur or isolator, wait 30 seconds, then switch back on. Check if the F9 returns.
6. Look for obvious signs of leaks around the boiler and pipework and listen for unusual pump noise (seized or noisy pump) which can indicate circulation problems.
Specific diagnostic/fix guidance (for an engineer or to prepare for a call-out):
- If pressure and simple circulation fixes (bleeding radiators, topping up) do not clear the fault, the cause may be: a sensor fault (flow thermistor or pressure sensor), pump failure, blocked/partially blocked heat exchanger, airlock in the system, or an electronics/PCB configuration problem.
- If the boiler has recently had a PCB or boiler chip card replaced, or recent electrical work was done, F9 can mean the PCB has not been configured or the wrong BCC has been fitted. A qualified engineer will check the PCB part numbers, the chip card seating, and programme or fit the correct chip card if required.
- If water ingress or corrosion is suspected (signs of water on the PCB or burnt components), turn the boiler off and call a Gas Safe engineer — damaged electronics require professional replacement and inspection for underlying leaks.
- If the pump looks seized or is not circulating, an engineer will test pump operation, check wiring to the pump, and clear any blockages or replace the pump if necessary.
- Sensor and wiring faults: a Gas Safe engineer will test the flow and return thermistors/pressure sensor resistances, check wiring and connectors to the PCB and replace faulty sensors or repair wiring as required.
When to call a professional:
- Call a Gas Safe registered heating engineer if the F9 fault remains after you have tried the safe initial checks (pressure top-up, bleeding radiators, single reset, power-cycle) or if you see signs of water leaks, electrical burning, or recent PCB/electrical work.
- Do not attempt to open the boiler or replace the PCB, chip card or sensors yourself. Only a qualified engineer should handle PCB configuration, replacement chip cards, gas valve or pump replacements, and internal wiring.
Information to give the engineer when you call:
- Exact fault code (F9), boiler model, serial number, and whether both heating and hot water are affected.
- Recent maintenance or electrical work, whether the PCB or chip card was recently replaced, and what steps you have already tried (pressure topped up, radiators bled, reset attempted).
- Any visible signs you noticed (leaks, scorch marks, unusual noises).
Following these checks will help you and the engineer identify whether the issue is a simple circulation/pressure problem you can safely fix or a PCB/configuration or component failure requiring professional repair or parts replacement.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Ideal Ideal Boiler.