Chaffoteaux 604 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 604 fault code mean?
Fault code 604 on a Chaffoteaux boiler means the boiler's control board has detected that the fan is spinning too slowly — or not spinning at all — and has locked the boiler out as a safety precaution. The fan serves two vital purposes: it draws fresh air into the combustion chamber and expels the burned gases through the flue. Without adequate fan speed, safe combustion cannot take place, so the boiler refuses to fire. This code appears on Chaffoteaux models with a digital display (such as the Pigma, Inoa, and Talia ranges). If you have an older Chaffoteaux with LED flash codes rather than a numeric display, consult your model's specific documentation as the fault-indication system differs.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Worn or failing fan motor Common
The fan motor weakens with age and accumulated running hours. An ageing motor may no longer reach the minimum speed the boiler expects, causing the control board to lock out. This is the single most frequent cause of a 604 on older Chaffoteaux appliances.
- Worn or seized fan bearings Common
The bearings that allow the fan impeller to spin freely can wear out or seize over time, particularly if the boiler has been making a grinding or rattling noise before the lockout. Seized bearings prevent the fan from reaching the correct speed.
- Loose or corroded electrical connections Common
The small vibrations a fan generates over years of operation can gradually loosen the wiring between the fan and the PCB. Once that connection is poor or intermittent, the PCB cannot confirm the fan is running at the right speed and triggers a lockout.
- Blocked or partially obstructed flue Sometimes
Debris such as leaves, a bird's nest, ice, or accumulated soot can restrict the flue outlet, preventing the fan from shifting gases at its normal rate. The reduced airflow registers as a fan-speed problem even if the fan motor itself is healthy.
- Faulty air pressure switch Sometimes
The air pressure switch monitors the draught created by the fan. If the switch has drifted out of calibration, has a cracked diaphragm, or a blocked sensing tube, it may report insufficient airflow even when the fan is spinning correctly, triggering code 604.
- Damaged fan blades Rare
Physical damage to the impeller — from debris ingestion or impact — can unbalance the fan and reduce its effective speed. This is less common but can occur in boilers that haven't had regular servicing.
- Faulty PCB Rare
A PCB that is misreading the fan's tachometer signal, or sending incorrect voltage to the fan motor, can produce a 604 even when the fan itself is undamaged. PCB faults are usually only confirmed after the fan and wiring have been ruled out.
How to fix it
- Check that the gas supply to the boiler is on DIY safe
Confirm the gas isolation valve on the supply pipe to the boiler is fully open (handle in line with the pipe). Check that other gas appliances in the home are working. If there is no gas supply, contact your gas supplier — do not attempt to investigate further yourself.
- Inspect the external flue terminal for obvious blockages DIY safe
Go outside and visually inspect the flue outlet on the wall or roof. Look for visible debris, ice build-up, or evidence of a bird's nest blocking the terminal. Do not attempt to dismantle anything; simply note what you can see so you can tell the engineer.
- Reset the boiler once DIY safe
Press and hold the reset button on the boiler's front panel for approximately 3 seconds, then release. Wait at least 60 seconds to see if the boiler fires and runs normally. If it immediately locks out again and redisplays code 604, do not keep resetting — repeated resets on a fan fault will not resolve the underlying problem and can mask important diagnostic information for the engineer.
- Check and restore system pressure if low DIY safe
Look at the pressure gauge on the boiler. It should read between 1.0 and 1.5 bar when the system is cold. If it is below 1.0 bar, top it up using the filling loop following your boiler's user guide. Note that low pressure alone will not cause code 604, but it is good practice to eliminate it before calling out an engineer.
- Have a Gas Safe engineer inspect the fan, wiring, and connections Gas Safe engineer
A registered engineer will check the fan motor's electrical supply and tachometer output, inspect all wiring connections between the fan and PCB for looseness or corrosion, and test the fan under operating conditions. Loose connections can often be secured at relatively low cost; a worn motor will require the fan assembly to be replaced.
- Have the engineer test or replace the air pressure switch Gas Safe engineer
If the fan checks out, the engineer should test the air pressure switch and its sensing tube for blockages, diaphragm failure, or calibration drift. A faulty switch is a straightforward replacement but must be carried out by a qualified professional.
- Clear any confirmed flue blockage Gas Safe engineer
If the visual check revealed a blocked flue terminal, the engineer can safely clear the obstruction and check that the flue system is correctly sealed and unobstructed throughout its run. Never attempt to access or clear internal flue sections yourself.
- Have the PCB tested if other components are healthy Gas Safe engineer
If the fan, wiring, air pressure switch, and flue are all found to be in good order, the engineer should test the PCB with a multimeter to confirm it is sending and receiving correct signals. A faulty PCB will require replacement by the engineer.
- Call a Gas Safe registered engineer if the fault persists or you are unsure at any stage Gas Safe engineer
Fault code 604 almost always requires hands-on diagnosis by a Gas Safe registered engineer. You can verify an engineer's registration at gassaferegister.co.uk. Given the potential safety implications of a fan fault — including the risk of incomplete combustion — do not continue using the boiler if it will not stay running after a single reset.
Parts you may need
- Boiler fan assembly (replacement unit) · from £150
- Air pressure switch · from £40
- Fan wiring harness / loom · from £25
- PCB (printed circuit board) · from £280
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £150–£400, depending on the underlying cause.
Frequently asked questions
Can I fix a Chaffoteaux 604 fault myself?
No. While you can safely reset the boiler once and check for obvious external flue blockages, the underlying cause of code 604 almost always involves internal components — the fan motor, bearings, wiring, air pressure switch, or PCB. Working on any of these requires a Gas Safe registered engineer. Attempting gas-appliance repairs yourself is illegal in the UK and potentially dangerous.
How much does it cost to fix a Chaffoteaux 604 fault?
For most homeowners the repair falls between £150 and £400. A wiring fix or fan-speed adjustment at the lower end involves labour only (typically £80–£150). A full fan-assembly replacement, including parts and labour, usually comes to £200–£400 depending on the specific Chaffoteaux model. An air pressure switch replacement is generally £100–£200 all-in. PCB replacement is more expensive — often £350–£550 — and if your boiler is over 10 years old, it may be worth getting a new-boiler quote at the same time.
Why does my Chaffoteaux keep showing 604 after I reset it?
A fault code that returns immediately or within a few firing cycles means the root cause has not been resolved. The most likely reasons are a mechanically worn fan motor that cannot sustain the required speed, seized bearings, a persistently faulty air pressure switch, or a PCB issue. Repeated resets will not fix any of these — they will simply cause repeated lockouts. Stop resetting and call a Gas Safe engineer to diagnose and repair the fault properly.
Could a frozen condensate pipe cause a Chaffoteaux 604 fault?
Indirectly, yes. A blocked or frozen condensate pipe can cause back-pressure fluctuations inside the boiler, which may interfere with airflow sensing and trigger fan-related fault codes including 604. In cold weather, check whether the condensate pipe (usually a plastic pipe running to an outside drain) is frozen. If it is, you can safely thaw it yourself using warm — not boiling — water poured over the external section. Once thawed, reset the boiler. If the 604 code persists, there is a separate underlying fault that needs engineer attention.