Chaffoteaux 706 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 706 fault code mean?
On Chaffoteaux boilers, '706' is not a conventional three-digit numeric code. These boilers use a flashing LED binary system, and what homeowners read as '706' is almost always the LEDs labelled 70 and 80 flashing together (sometimes also described as the 40+60+80 combination). This pattern points to a breakdown in communication between the fan and the air pressure switch (APS). Either the fan is running but the APS is not confirming adequate airflow to the PCB, or the fan is off but the APS has failed to return to its resting (off) position. In both cases the PCB cannot verify that harmful combustion gases are being safely expelled through the flue, so as a precaution it locks out gas flow and shuts the boiler down. Until the PCB receives a clean signal from the APS confirming the fan is working correctly, the boiler will not fire.
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
- Blocked or dirty fan venturi tubes Common
Short heat-resistant tubes connect the fan venturi to the air pressure switch. Dust, debris, or combustion residue can partially block these tubes, starving the APS of the pressure differential it needs to operate. Engineers frequently resolve this fault simply by cleaning the fan assembly, venturi ports, and associated tubing — no parts needed.
- Faulty or stuck air pressure switch Common
The APS is a small diaphragm switch that should click open and closed in response to fan airflow. Over time the diaphragm can stick, crack, or the switch contacts corrode. When the switch is made but fails to return to its resting position, the PCB receives a contradictory signal and locks out. A Gas Safe engineer can test it by checking continuity with a multimeter and listening for the audible click.
- Loose wiring connections on the fan or APS Sometimes
Chaffoteaux wiring looms use crimp (Lucar-style) terminals similar to car audio connectors. These can work loose with vibration over time. A poor connection on either the fan supply wires or the APS signal wires produces exactly the same symptom as a failed component. Re-seating all connectors is a free first check.
- Faulty PCB relay not driving the fan Sometimes
If the fan is completely silent when it should be running, the fault may lie upstream on the PCB. A specific relay (the Takamisawa JV24SG-KT type, found on the right-hand side of the PCB near the APS wiring) is known to fail on some Chaffoteaux boards. The fan never starts, so the APS never closes, and the boiler locks out. Replacing the relay — or in some cases the full PCB — resolves this.
- Frozen condensate pipe Rare
In cold weather, the external section of the condensate drain pipe can freeze solid, causing the boiler to shut down. Look for a white plastic pipe (typically 21 mm or 32 mm) exiting through an external wall, often close to the ground. If it feels solid or has visible ice, thawing it is a straightforward DIY task.
How to fix it
- Check whether the condensate pipe is frozen DIY safe
In cold weather, locate the white plastic condensate pipe on the outside wall. If it is frozen, pour warm (not boiling) water along it or wrap it with a hot-water bottle until it thaws. Once clear, reset the boiler using the reset button — press it once and wait up to two minutes for a normal start.
- Reset the boiler once DIY safe
Press the reset button once and wait. If the boiler fires and runs normally, monitor it over the next hour. If the fault returns promptly, do not keep resetting — repeated resets will not fix an underlying fault and may mask a developing safety issue.
- Inspect and re-seat all wiring connectors on the fan and air pressure switch Gas Safe engineer
A Gas Safe engineer should remove and firmly re-seat every crimp/Lucar terminal on the fan wiring loom and on the two wires connecting to the air pressure switch. Corroded or loose terminals are a common free fix and should always be checked before replacing components.
- Clean the fan, venturi, and APS tubes Gas Safe engineer
An engineer will remove the fan assembly and clear any dust or residue from the venturi ports and the small silicone tubes linking the venturi to the air pressure switch. This is the single most common resolution for this fault on Chaffoteaux boilers and costs nothing in parts.
- Test and replace the air pressure switch if faulty Gas Safe engineer
Using a multimeter the engineer can confirm whether the APS contacts are switching correctly in response to airflow. A gentle suction on the silicone tube should produce an audible click; if it does not, or if continuity is absent, the switch needs replacing. This is a relatively low-cost repair.
- Inspect the PCB relay and replace if necessary Gas Safe engineer
If the fan is not receiving any drive voltage, the engineer should check the PCB relay (Takamisawa JV24SG-KT or equivalent) on the right-hand side of the board. Both relays in that cluster are typically replaced together. If wider PCB damage is found, a full board replacement may be needed — at which point the age and overall condition of the boiler should factor into the decision.
- Call a Gas Safe registered engineer if the fault persists Gas Safe engineer
If the steps above have not resolved the fault, or if you have not been able to carry out the engineer checks yourself, book a Gas Safe registered engineer. This fault disables the boiler as a safety measure and should not be ignored, particularly in cold weather.
Parts you may need
- Air pressure switch (APS) · from £35
- Fan motor / fan assembly · from £110
- PCB relay (Takamisawa JV24SG-KT or equivalent) · from £8
- Full PCB replacement · from £220
- APS silicone connecting tube · from £6
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
Why does my Chaffoteaux boiler show '706' — is that a real fault code?
Chaffoteaux boilers do not use a numeric display in the way modern boilers do. The '706' appearance is caused by LEDs 70 and 80 flashing simultaneously on the boiler's indicator panel — this is a documented fault pattern pointing to a fan and air pressure switch communication problem. If your boiler's display or LED array is showing what looks like '706', you are looking at this fault.
Can I fix the Chaffoteaux 706 fault myself?
There are two safe DIY checks: thawing a frozen condensate pipe in winter, and pressing the reset button once. Everything else — cleaning the fan, testing the air pressure switch, inspecting wiring, or touching the PCB — must be done by a Gas Safe registered engineer. The boiler locks out on this fault for a safety reason, so it should not be bypassed.
How much does it cost to repair a Chaffoteaux 706 fault?
Most people pay between £120 and £350. Replacing the air pressure switch with labour typically falls in the £120–£180 range, while a fan assembly replacement is usually £200–£300. A full PCB replacement can cost £350–£500 or more and is worth weighing against the cost of a new boiler if yours is over 12 years old.
My Chaffoteaux boiler keeps coming back to the 706 fault after I reset it — what should I do?
A fault that returns within minutes of a reset almost certainly has a physical cause — most commonly a dirty fan venturi, a stuck air pressure switch, or a loose wiring connector. Stop resetting and book a Gas Safe engineer. Repeated resets will not cure the underlying problem and may delay identifying a genuine safety issue with the flue system.