Chaffoteaux 2P3 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 2P3 fault code mean?
If your Chaffoteaux boiler is displaying what looks like '2P3', you are almost certainly seeing the code '5P3' — the digit '5' on Chaffoteaux digital displays can closely resemble a '2' (or an 'S') depending on the screen font and viewing angle, which is a well-known source of confusion. The genuine code 5P3 (sometimes written SP3) signals flame cut-off during operation. Unlike the related codes 5P1 and 5P2 — which indicate that one or two ignition attempts failed before a flame was ever established — 5P3 means the boiler did detect a flame but then lost it while running, a condition sometimes described as flame detachment. The boiler locks out as a safety measure and will require attention before it restarts. 5P3 is a non-volatile error on Chaffoteaux boilers, meaning it will not clear itself automatically and requires a manual reset once the underlying cause is resolved.
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
- Dirty or Damaged Ignition/Ionisation Electrode Common
The ionisation electrode detects and confirms that a flame is present. If it is coated with carbon deposits, corroded, cracked, or poorly positioned, it cannot reliably sense the flame after ignition — the boiler's control board then concludes the flame has been lost and triggers 5P3. This is the most frequent root cause found during engineer call-outs for this code.
- Interrupted or Low-Pressure Gas Supply Common
If the gas supply pressure is too low, interrupted, or air has entered the line — particularly after a long period of inactivity or following work on the gas network — the flame may light briefly but then die away. The boiler interprets this as flame detachment and locks out with 5P3.
- Blocked or Obstructed Flue / Poor Combustion Draft Sometimes
Adequate draft through the flue is essential for stable combustion. A partial blockage, bird's nest, ice on the terminal in winter, or an incorrectly installed flue can disrupt airflow enough to destabilise the flame after ignition, causing it to detach and triggering 5P3.
- Faulty or Obstructed Combustion Fan Sometimes
The fan draws combustion air through the burner and pushes flue gases out. If the fan is clogged with debris, running at the wrong speed, or starting to fail, combustion becomes unstable and the flame may not be sustained, resulting in 5P3.
- Gas Valve Fault Sometimes
The gas valve regulates fuel flow to the burner under instruction from the PCB. A valve that sticks, modulates incorrectly, or fails to hold the correct flow rate can cause the flame to weaken and cut out after initial ignition. Diagnosis requires resistance and voltage testing by a Gas Safe engineer.
- PCB (Printed Circuit Board) Failure Rare
If the ignition sequence appears to run normally but the boiler still locks out with 5P3, the PCB itself may be failing to correctly process the ionisation signal — even when the electrode is functioning. A faulty PCB can misinterpret a healthy flame as absent, or fail to keep the gas valve open once ignition is confirmed.
How to fix it
- Check that your gas supply is active DIY safe
Before anything else, confirm that your gas supply is on. Check whether other gas appliances in your home — a gas hob, for example — are working normally. If they are not, there may be a supply issue affecting the whole property; contact your gas supplier. Also make sure the isolation valve on the gas pipe to the boiler is fully open (handle in line with the pipe).
- Reset the boiler once DIY safe
Press and hold the reset button on your Chaffoteaux boiler as described in your user guide (typically 3–5 seconds). Allow the boiler to complete its ignition sequence. If the fault clears and the boiler runs normally, monitor it over the next day or two. Do not repeat the reset more than two or three times in total — repeated resets without resolving the underlying cause can mask a safety-relevant problem, and some Chaffoteaux models limit the number of permitted resets as a safeguard.
- Inspect the flue terminal for obvious external blockages DIY safe
Go outside and visually check the flue outlet (the pipe exiting through the wall or roof). Look for any obvious obstruction such as a bird's nest, debris, or ice around the terminal in cold weather. Do not attempt to dismantle the flue — this is simply a visual check. If you can see a clear blockage at the terminal, report it to your engineer. In freezing conditions, ice build-up on a plastic flue terminal is a known cause of combustion issues.
- Call a Gas Safe registered engineer for diagnosis Gas Safe engineer
If the fault returns after a single reset, or the boiler will not restart at all, you need a Gas Safe registered engineer to investigate. They will inspect and test the ionisation/ignition electrode and its leads, measure gas supply pressure at the boiler, check the fan operation and flue integrity, test the gas valve electrically, and evaluate the PCB if all other components check out. Attempting to work on any of these components yourself is unsafe and illegal without Gas Safe registration.
- Agree a repair or replacement plan with your engineer Gas Safe engineer
Once the engineer identifies the faulty component, they will advise on repair costs versus the age and condition of the boiler. On older Chaffoteaux models, parts availability can be limited, so weigh up the repair quote against the cost of a new boiler — particularly if the boiler is more than 10–12 years old.
Parts you may need
- Ionisation / ignition electrode and lead set · from £45
- Combustion fan assembly · from £120
- Gas valve · 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 £120–£350, depending on the underlying cause.
Frequently asked questions
Is 2P3 definitely the same as 5P3 on a Chaffoteaux boiler?
Almost certainly yes. Chaffoteaux boilers display the code '5P3', but the digit '5' on many Chaffoteaux display screens has a font that can easily look like a '2' or an 'S' at a glance, especially if the screen is slightly dirty or viewed at an angle. The code 2P3 does not appear in any Chaffoteaux documentation, while 5P3 is a well-documented flame-loss fault. If your display shows what appears to be '2P3', treat it as 5P3.
What is the difference between 5P1, 5P2, and 5P3 on a Chaffoteaux boiler?
These three codes all relate to the ignition and flame-proving sequence, but they occur at different stages. 5P1 means the boiler failed on its first ignition attempt — no flame was established. 5P2 means it also failed on the second attempt. 5P3 is different in an important way: it means the boiler did detect a flame but then lost it during operation. Because 5P3 involves flame detachment rather than simply a failed spark, it often points to issues with flame stability — such as a dirty ionisation electrode, gas supply irregularity, or a flue/fan problem — rather than a straightforward ignition failure.
Can I keep resetting my Chaffoteaux boiler to clear the 5P3 fault?
You should reset it no more than two or three times. If the fault clears on the first reset and the boiler runs without issue, monitor it closely. But if the fault returns, repeated resets are not a solution — they simply mask the underlying problem and will not prevent the boiler from locking out again. Some Chaffoteaux models also limit the total number of permitted resets as a built-in safety feature. A Gas Safe registered engineer should carry out a proper diagnosis.
How much does it typically cost to fix a Chaffoteaux 5P3 fault in the UK?
For the most common cause — a worn or dirty ignition/ionisation electrode — you would typically pay £120–£200 including parts and labour. A fan replacement usually falls in the £200–£350 range. Gas valve work tends to cost £150–£300. If the PCB turns out to be the cause, parts and labour can push the total to £400–£550 or more, which on an older boiler may prompt a conversation about replacement instead. Most homeowners with this fault end up paying somewhere in the £120–£350 range once the engineer has diagnosed and resolved the issue.