Chaffoteaux 5P1 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 5P1 fault code mean?
The 5P1 code on a Chaffoteaux boiler is a notification indicating that the boiler has failed on its first ignition attempt. It is worth noting that many users misread this code as 'SP1' because the digit '5' on the boiler's display can look like the letter 'S' — but 5P1 is the correct reading. The code itself is not a hard lockout fault in isolation; rather, it flags the first of a sequence of failed start attempts. If the boiler fails to ignite three times in succession, it will lock out completely and will not restart automatically. Because 5P1 is a non-volatile notification, the boiler must be manually reset before it will try to fire again. The most common triggers are a gas supply interruption, a dirty or mispositioned ignition electrode, or a blocked burner, though a faulty gas valve or PCB can also be responsible in more serious cases.
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 interruption or low gas pressure Common
If the gas supply to the property is off, interrupted, or at unusually low pressure, the boiler simply has no fuel to ignite. This is the most common reason for a first-attempt ignition failure. Check whether other gas appliances in the home — such as the hob or gas fire — are working normally. If they are not, the issue lies with the wider supply rather than the boiler itself.
- Dirty or faulty ignition/ionisation electrode Common
The ionisation electrode detects whether a flame has been established. Over time it can accumulate carbon deposits, soot, or dust, which prevent it from reading the flame signal correctly. Physical damage to the ceramic holder — such as cracks or chips — or wiring that has broken or shorted to earth can produce the same result. A mispositioned electrode, perhaps knocked during a previous service, may also sit outside the combustion zone and fail to detect ignition.
- Blocked burner or injectors Sometimes
Dust, soot, or debris blocking the burner nozzles can restrict gas flow to the point where reliable ignition is impossible. This is more likely in boilers that have not been serviced recently or that are installed in particularly dusty environments.
- Faulty gas valve Sometimes
The gas valve controls the flow of fuel into the burner. If the valve is not opening fully — or at all — the burner will not receive enough gas to sustain a flame. A faulty valve can cause intermittent or persistent ignition failures and must be tested and replaced by a Gas Safe engineer.
- Condensation on the electrodes Sometimes
Boilers installed in unheated spaces such as garages or outbuildings can suffer from condensation forming on the ignition electrodes, particularly after a cold night or a period of inactivity. This moisture can prevent a spark from forming or stop the ionisation circuit from completing correctly.
- Faulty PCB (printed circuit board) Rare
If the ignition sequence appears to run normally but the boiler still locks out with 5P1, the control board may not be recognising or processing the flame signal correctly. PCB faults can sometimes be spotted visually — look for discolouration, melted or swollen components, or damaged circuit traces — but confirmation and replacement require a qualified engineer.
How to fix it
- Check that other gas appliances are working DIY safe
Before resetting the boiler, go to your gas hob or any other gas appliance in the home and check it lights or operates normally. If nothing gas-powered works, the problem is with the incoming gas supply — contact your gas supplier rather than repeatedly resetting the boiler.
- Reset the boiler once DIY safe
Press the reset button on the boiler's front panel and wait for it to attempt ignition. Allow at least 60 seconds after the reset before concluding whether it has fired successfully. If it locks out again immediately, attempt a second reset after a short wait. Do not reset more than two or three times in total — repeated resets without the boiler firing can, in rare cases, allow unburnt gas to accumulate.
- Check and top up system pressure if low DIY safe
Although low system pressure is more commonly linked to heating and hot water faults rather than ignition failures, it is worth checking the pressure gauge while you have the boiler panel open. Most Chaffoteaux boilers operate correctly between 1.0 and 1.5 bar when cold. If the pressure is below 0.5 bar, top it up via the filling loop and then attempt a reset. Refer to your user manual for the location of the filling loop on your specific model.
- Check for a frozen condensate pipe (in cold weather) DIY safe
If the fault has appeared during freezing temperatures, the external condensate pipe may be blocked with ice. This typically triggers a different code, but a frozen pipe can indirectly affect boiler operation. Thaw the pipe gently with warm (not boiling) water poured along its length, then reset the boiler.
- Engineer: inspect, clean, or replace the ignition and ionisation electrode Gas Safe engineer
A Gas Safe engineer will access the electrode assembly, check its position relative to the burner, and clean off any carbon deposits or contamination. If the ceramic holder is cracked, the electrode is damaged, or the wiring has broken down, the assembly will need replacing. This is one of the most common resolutions for persistent 5P1 faults.
- Engineer: inspect and clean the burner and injectors Gas Safe engineer
With the boiler isolated from the gas and electrical supply, the engineer will remove and inspect the burner. Blocked injector nozzles are cleaned or replaced, and any debris inside the combustion chamber is removed. The burner is then reassembled and the boiler tested through a full ignition sequence.
- Engineer: test the gas valve Gas Safe engineer
Using a multimeter, the engineer will measure the resistance of the gas valve coil windings to determine whether it is operating within specification. On units fitted with the SIT Sigma valve, expected readings are approximately 6.5 kΩ between terminals 1 and 3, and 7.4 kΩ between terminals 1 and 4. A valve that falls outside these parameters will need to be replaced like-for-like by a Gas Safe engineer.
- Engineer: assess the PCB Gas Safe engineer
If all other components check out correctly, the engineer will examine the control board for signs of damage and test whether it is correctly processing the flame ionisation signal. A defective PCB will need to be replaced. Given the age of some Chaffoteaux models, sourcing the correct board may require going through the Ariston Group parts network.
- Call a Gas Safe registered engineer if the fault persists Gas Safe engineer
If the boiler continues to display 5P1 or locks out after your initial reset attempts, stop resetting and arrange for a Gas Safe registered engineer to carry out a full diagnosis. You can find registered engineers at gassaferegister.co.uk. Always ask the engineer to show their Gas Safe ID card before allowing work to begin.
Parts you may need
- Ignition / ionisation electrode assembly · from £35
- Electrode lead / HT ignition cable · from £20
- Burner injector set · from £45
- Gas valve (e.g. SIT Sigma compatible) · from £95
- PCB / main control board · from £180
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–£350, depending on the underlying cause.
Frequently asked questions
Is 5P1 the same as SP1 on a Chaffoteaux boiler?
Yes — they are the same code. The confusion arises because the digit '5' on Chaffoteaux boiler displays can look very similar to the letter 'S', so many users read it as 'SP1'. The correct code is 5P1, and it indicates the boiler's first failed ignition attempt.
Can I keep resetting the boiler to clear the 5P1 code?
You can try one or two resets to see if the boiler fires successfully after a transient issue such as a brief gas supply interruption. However, repeatedly resetting without the boiler igniting is not recommended — it will not fix an underlying fault and in theory allows repeated attempts to push unburnt gas into the flue. If the fault returns after two or three resets, call a Gas Safe registered engineer.
How much does it cost to fix a Chaffoteaux 5P1 fault?
For most homeowners, the repair falls somewhere between £150 and £350 including parts and labour. Cleaning or replacing an ignition electrode is typically at the lower end of that range, while a gas valve replacement usually comes in around £180–£220 all-in. If the PCB needs replacing, costs can rise to £300–£450 or more depending on board availability, which is worth factoring in if the boiler is already over ten years old.
My Chaffoteaux boiler is old — is it worth repairing a 5P1 fault or should I replace it?
Chaffoteaux boilers generally have a lifespan of around 10 to 15 years with regular servicing. If your boiler is within that range and the fault is simply a dirty electrode or minor burner issue, a repair is usually good value. If it is approaching or past 15 years and requires an expensive component such as a PCB, heat exchanger, or gas valve, the cost of repair can start to approach the cost of a new boiler — in which case a replacement is often the more economical long-term choice. Ask your engineer for an honest assessment before committing to a costly repair on an ageing appliance.