Chaffoteaux 5P4 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 5P4 fault code mean?
The 5P4 code appears on Chaffoteaux boilers after four consecutive failed attempts to ignite the burner. Chaffoteaux boilers run through a structured ignition-attempt sequence — 5P1 through 5P6 — where each code represents one more failed try. If the boiler lights on the second attempt, it stops at 5P2 and carries on normally; if it keeps failing, the code steps up through 5P3 and then 5P4. By this stage the boiler has given up and locked out, meaning it will not restart by itself and needs a manual reset. Note that the digit '5' on the display closely resembles the letter 'S', so many users read this code as 'SP4' rather than '5P4' — both refer to the same fault. Because this is a non-volatile lockout, power cycling alone will not clear it; you must press the reset button on the front panel.
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
- Gas supply interrupted or isolation valve closed Common
The most frequent trigger for repeated ignition failures is simply no gas reaching the burner. The boiler-isolation valve (typically beneath or beside the boiler) may have been accidentally turned off, or there could be a wider supply outage affecting other gas appliances in your home.
- Faulty or carbon-fouled ignition/ionisation electrode Common
The electrode must generate a reliable spark to light the gas and then confirm the flame is present. If it is cracked, worn, or coated in carbon deposits, sparking becomes inconsistent and the boiler fails to detect ignition — triggering the 5Px sequence until lockout.
- Low gas pressure at the boiler Sometimes
Even when the supply is on, gas pressure that falls below the manufacturer's minimum level means the burner cannot establish a stable flame. This is more common in older properties, during periods of high network demand, or if a regulator is beginning to fail.
- Air trapped in the gas line Sometimes
After a prolonged period of inactivity, or following work on the gas pipework, air can become trapped in the supply line to the boiler. The boiler then fires into an air pocket rather than gas, failing to ignite on each attempt.
- Gas valve failure Sometimes
The gas valve is an electromechanical component controlled by the PCB. If it sticks, fails to open fully, or its coil resistance drifts out of specification, the correct volume of gas never reaches the burner. An engineer will measure the valve electrically before condemning it.
- Ionisation electrode wiring fault Sometimes
The wiring that carries the flame-sense signal back to the PCB can suffer from loose connections, heat damage, or corrosion. If the PCB never receives a positive flame signal, it treats every ignition attempt as a failure even when a flame is briefly established.
- Faulty PCB (control board) Rare
If all the ignition components test within specification but the lockout persists, the PCB itself may be misinterpreting sensor readings or failing to trigger the ignition sequence correctly. This is a less common but more expensive diagnosis.
- Frozen or blocked condensate pipe Rare
In cold weather a blocked condensate pipe can cause the boiler to lock out repeatedly. Although this is more typically associated with condensate-specific fault codes, it can contribute to ignition failures on some Chaffoteaux models if back-pressure affects the flue.
How to fix it
- Check that gas is available at other appliances DIY safe
Turn on a gas hob or check another gas appliance in the property. If nothing else has gas either, the issue is a supply interruption — contact your gas network operator (e.g. Cadent, Wales & West, SGN) rather than a boiler engineer.
- Confirm the boiler isolation valve is fully open DIY safe
The gas isolation valve is usually a quarter-turn lever located on the pipe feeding into the boiler. When it is in line with the pipe it is open; when it sits across the pipe it is closed. Make sure it is fully open before proceeding.
- Check the system pressure reads between 1 and 1.5 bar DIY safe
Look at the pressure gauge on the front of the boiler. If it reads below 1 bar, top up via the filling loop — a braided flexible connector beneath the boiler with one or two valves. Open slowly until the gauge reaches about 1.2–1.5 bar, then close the valve(s). If the boiler regularly loses pressure, mention this to the engineer as it points to a separate issue such as a leak or faulty expansion vessel.
- Check for a frozen condensate pipe (winter months only) DIY safe
The condensate pipe is typically a white or grey plastic pipe (often 21.5 mm diameter) running from the boiler to an outside drain or soakaway. If outdoor temperatures have been below freezing and the pipe feels solid, it may be frozen. You can carefully pour warm (not boiling) water along the external section or wrap it with a hot-water bottle to thaw it.
- Reset the boiler once using the front-panel reset button DIY safe
Press and hold the reset button (often marked with a flame and an 'X', or labelled 'Reset') for the time specified in your boiler manual — usually 3–5 seconds. Allow the boiler a full 60 seconds to attempt a restart. If it lights successfully, monitor it for the next few hours. If it locks out again, attempt one further reset. Do not reset the boiler more than twice in quick succession; Chaffoteaux boilers limit the number of permitted resets for safety reasons, and persistent lockouts signal a fault that needs professional diagnosis.
- If the fault persists, call a Gas Safe registered engineer Gas Safe engineer
A Gas Safe engineer will carry out a systematic ignition-system inspection: checking spark generation at the electrode, measuring ionisation current, testing the gas valve electrically, verifying gas inlet pressure with a manometer, and inspecting all associated wiring. They will clean or replace the electrode if fouled, purge the gas line if air is present, or replace the gas valve or PCB if either is found to be defective. Always ask to see the engineer's Gas Safe ID card before work begins.
Parts you may need
- Ignition/ionisation electrode · from £35
- Electrode lead/wiring harness · from £25
- Gas valve (Chaffoteaux compatible) · from £120
- PCB (main control board) · from £220
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 display show SP4 instead of 5P4?
The digit '5' on Chaffoteaux LED and LCD displays is easily mistaken for the letter 'S', so 'SP4' and '5P4' are the same fault code. The full ignition-attempt sequence runs from 5P1 to 5P6, with each step representing one more failed ignition attempt. By 5P4, the boiler has tried and failed four times and has locked itself out.
Can I fix the 5P4 fault myself, or do I need an engineer?
Homeowners can safely carry out a few basic checks: confirming the gas supply is on, making sure the isolation valve is open, topping up the system pressure if it has dropped below 1 bar, and pressing the reset button once or twice. Beyond that, all further work — inspecting or replacing the electrode, testing the gas valve, or diagnosing the PCB — must be done by a Gas Safe registered engineer. Attempting gas-related repairs without registration is illegal in the UK and potentially dangerous.
How much does it typically cost to fix a Chaffoteaux 5P4 fault?
Most homeowners pay between £120 and £350 to resolve a 5P4 lockout. A straightforward electrode clean or replacement, including an engineer's call-out and labour, usually falls in the £120–£180 range. A gas valve replacement typically costs £200–£350 once parts and labour are included. PCB replacement is considerably more expensive — often £450–£700 — but this is a less common outcome; if the PCB is at fault on an older boiler, it is worth getting a replacement boiler quote at the same time.
My boiler keeps showing 5P4 every few days. What is causing it?
Recurring ignition lockouts usually point to a component that is deteriorating rather than completely failed — a worn electrode that works intermittently, a gas valve that is beginning to stick, or slowly falling gas pressure. An engineer should carry out a full ignition-system service rather than simply resetting the boiler each time. Repeated lockouts also accelerate wear on other components, so the sooner it is investigated, the cheaper the repair is likely to be.