Chaffoteaux 608 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 608 fault code mean?
Fault code 608 indicates that your Chaffoteaux boiler's combustion fan has started up as normal, but the air pressure switch — the safety device that must confirm adequate airflow before the boiler can ignite — has not closed (activated) as expected. Without this confirmation signal, the boiler cannot be sure that safe combustion conditions exist, so it shuts down as a precaution. In Chaffoteaux's 600-series fault group, code 607 means the pressure switch tripped unexpectedly before ignition, whereas 608 is the opposite scenario: the fan is running but the switch simply hasn't responded. Codes 6P1 and 6P2, which indicate a delay in the pressure switch contact closing, are also related faults you may encounter on the same Ariston-platform models.
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
- Faulty air pressure switch Common
The pressure switch itself has failed mechanically or electrically and will not close even though the fan is spinning at normal speed. This is the most common finding when a Gas Safe engineer investigates code 608 — the switch needs testing for continuity and, in most cases, replacing.
- Loose, corroded, or damaged wiring to the pressure switch Common
Chaffoteaux's own guidance for this fault specifically calls out checking the pressure switch and all its connections. A loose pin, corroded connector, or chafed wire between the switch and the PCB can break the signal circuit without the switch itself being defective.
- Blocked, kinked, or split pressure switch tubing Common
A small rubber hose links the pressure switch to the fan or Venturi assembly. Over time this hose can accumulate condensate, kink, or develop a split. If the hose cannot convey the pressure differential from the fan, the switch never receives the signal it needs to activate, even if the fan and switch are both healthy.
- Damaged or melted Venturi tube Sometimes
If the boiler has previously overheated — for example, if it was fired up with an unfilled heating system or after a long period of inactivity that allowed air to accumulate in the heat exchanger — the lower section of the Venturi tube can warp or partially melt. A small hole or deformation allows air to bypass, reducing the pressure differential and preventing the switch from tripping.
- Fan generating insufficient pressure Sometimes
If the fan motor is wearing out or running below its target speed, it may not create enough of a pressure differential to activate the switch, even though it appears to be running. This can be confirmed by an engineer testing the pressure output at the Venturi.
- PCB not reading the pressure switch signal correctly Rare
In a small number of cases all the mechanical components check out fine but the control board is failing to register the switch signal. PCB faults are the last thing to suspect once everything else has been ruled out.
How to fix it
- Attempt a single boiler reset DIY safe
Locate the reset button on your Chaffoteaux boiler (usually a button or rotary dial marked with a flame or reset symbol) and press it once. Wait two to three minutes to see whether the boiler fires successfully. If fault code 608 returns, do not keep resetting — repeated resets will not clear a component fault and can mask the underlying problem. Move to the next step.
- Check that your gas supply is working DIY safe
Confirm that other gas appliances in your home (hob, gas fire) are working normally. If they are not, contact your gas supplier rather than an engineer — the issue may be with the supply rather than the boiler.
- Check for an obvious external flue obstruction DIY safe
Take a look at the flue terminal on the outside wall of your property. In cold weather a heavily frosted or ice-blocked flue terminal can restrict airflow enough to affect pressure switch behaviour. If there is ice or debris, carefully clear it and try a reset. Do not touch any internal boiler components.
- Call a Gas Safe registered engineer to inspect the air pressure switch and its wiring Gas Safe engineer
An engineer will test the pressure switch for correct continuity and check that the wiring harness and connector pins to the switch are secure, undamaged, and free from corrosion. A faulty switch is the most likely culprit and is straightforward to replace with the correct part.
- Engineer to inspect the pressure switch hose and Venturi assembly Gas Safe engineer
The engineer will trace the small rubber tube from the switch back to the fan or Venturi, looking for kinks, cracks, condensate blockages, or signs of heat damage. The Venturi itself should be examined for warping or holes that could cause an air bypass. Both the hose and Venturi can be replaced as separate parts if defective.
- Engineer to test fan speed and pressure output Gas Safe engineer
Using appropriate test equipment the engineer will confirm that the fan is reaching the correct operating speed and generating the pressure differential specified for the boiler model. A fan that runs but underperforms may need cleaning, or the fan motor assembly may require replacement.
- Engineer to inspect the PCB if all other components are sound Gas Safe engineer
If the pressure switch, wiring, hose, Venturi, and fan all test within specification, attention turns to the PCB. The control board may have a failed relay or input circuit that prevents it reading the switch signal correctly. PCB diagnosis and replacement should only be carried out by a qualified engineer.
Parts you may need
- Air pressure switch · from £45
- Pressure switch rubber hose/tubing · from £12
- Venturi tube assembly · from £55
- Fan motor assembly · from £120
- PCB (printed circuit board) · from £200
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 £120–£350, depending on the underlying cause.
Frequently asked questions
Can I keep resetting the boiler to clear fault code 608?
It is fine to try one reset to see whether the fault was a one-off glitch, but you should not repeatedly reset a 608 lockout. The boiler is shutting down because it cannot confirm safe airflow, and cycling through multiple resets will not fix a faulty pressure switch, damaged hose, or worn fan. If the fault returns after a single reset, book a Gas Safe engineer.
How much does it cost to fix a Chaffoteaux 608 fault?
For most homeowners the repair falls between £120 and £350, covering the engineer's diagnosis visit plus the cost of replacing the air pressure switch, its hose, or related wiring — the most common findings. Fan motor replacement typically sits in the £200–£320 range including parts and labour. A PCB replacement is less common but can cost £250–£400 depending on parts availability. If your boiler is over 10–12 years old and requires a fan or PCB, it is worth getting a new boiler quote alongside the repair estimate.
What is the difference between fault codes 607, 608, 6P1, and 6P2 on a Chaffoteaux boiler?
These four codes all sit within Chaffoteaux's 600-series air pressure switch fault group. Code 607 means the pressure switch opened or tripped unexpectedly before ignition — the switch activated when it should not have. Code 608 is the opposite: the fan has started but the switch has not activated as expected. Codes 6P1 and 6P2 indicate that the pressure switch contact closed but with an unacceptable delay. All four faults point broadly at the same components — the pressure switch, its wiring, and the connecting hose — so the diagnostic approach is similar regardless of which code appears.
Could a blocked flue cause a Chaffoteaux 608 fault?
Yes, indirectly. If the flue terminal is heavily blocked — for instance by ice in winter or a bird's nest — airflow through the system is restricted and the fan may struggle to generate enough pressure differential to activate the pressure switch. Always check the external flue terminal before calling an engineer. That said, a restricted flue is only one of several possible causes, and the pressure switch or its hose is still more likely to be the root cause in most 608 cases.