Chaffoteaux 1P5 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 1P5 fault code mean?
The 1P5 code on a Chaffoteaux boiler indicates a failed ignition attempt — the boiler tried to light the burner, couldn't establish a flame, and has locked out. It is a non-volatile notification, meaning the boiler will not attempt to restart on its own; you must take action before it will fire again. Important display note: Chaffoteaux's segmented digital displays can make certain digits hard to read, and 1P5 is very commonly a misreading of 5P1 — the first in a three-stage ignition-failure sequence (5P1 → 5P2 → 5P3) that the boiler logs as each ignition attempt fails. If your display shows any of these codes, the root cause and the fix are the same: something prevented the burner from lighting. Until the underlying problem is resolved you will have no heating or hot water.
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 single most common reason a Chaffoteaux boiler fails to ignite is that gas simply isn't reaching the burner. This could be a closed service valve on the gas pipe to the boiler, a prepayment meter that has run out of credit, or a wider supply interruption in your street. Check that other gas appliances in the home — the hob, for example — are working normally.
- Dirty or mispositioned ignition/ionisation electrode Common
The ignition electrode creates the spark that lights the burner, while the ionisation electrode (sometimes the same component) detects the flame. Carbon deposits, corrosion, or a slight physical misalignment can prevent a reliable spark or cause the boiler to fail to sense the flame even when it does briefly light. This is one of the most frequent workshop findings on Chaffoteaux ignition faults.
- Low gas pressure or air in the gas line Sometimes
If the boiler has been dormant for an extended period, or if recent work has been carried out on the gas pipework, there may be air trapped in the supply line or insufficient gas pressure reaching the burner. Gas pressure issues require a Gas Safe engineer to measure and rectify.
- Flue or air-supply obstruction Sometimes
A blocked or partially obstructed flue prevents combustion gases from escaping, which in turn prevents the flame from establishing safely. Bird nests, debris around the flue terminal, or a kinked flue duct can all trigger this. Poor ventilation around an open-flued installation has the same effect.
- Faulty or sticking gas valve Sometimes
The gas valve controls the flow of fuel to the burner. If it has failed electrically or become stuck, gas will not reach the burner regardless of the ignition spark. A Gas Safe engineer can test the valve electrically and check for correct opening.
- Condensation on the electrodes Rare
In boilers installed in unheated outbuildings, garages, or utility rooms, moisture can condense on the ignition electrodes during cold weather. This dampens the spark and prevents reliable ignition. The combustion chamber needs to be allowed to dry out or be dried by a qualified engineer.
- Faulty PCB (printed circuit board) Rare
The control board orchestrates the entire ignition sequence. A failing PCB may not send the correct signal to the gas valve or ignition transformer, producing an ignition lockout with no obvious mechanical cause. This is usually only suspected after other components have been ruled out.
How to fix it
- Check that gas is available to the property DIY safe
Try a gas hob ring or another gas appliance. If nothing works, your gas supply may be off or your prepayment meter may need topping up. If gas is available elsewhere but still not at the boiler, locate the isolation valve on the gas pipe directly feeding the boiler (usually a quarter-turn lever near the appliance) and confirm it is fully open — the slot in the valve body should be parallel to the pipe.
- Check the boiler's system pressure DIY safe
Look at the pressure gauge on the boiler fascia. It should read between 1.0 and 1.5 bar when the system is cold. If it reads below 1 bar, top it up using the filling loop (a flexible braided hose with one or two valves, usually located beneath the boiler). Open the valve(s) slowly, watch the gauge, and close them once you reach about 1.2 bar. Do not overfill beyond 2 bar.
- Check for a frozen condensate pipe (winter months) DIY safe
Condensing boilers have a white plastic pipe, usually 21.5 mm or 32 mm diameter, that exits through an outside wall and drains acidic condensate. In freezing weather this can ice up and cause the boiler to lock out. If it feels solid, carefully thaw it by pouring warm (not boiling) water along the pipe or wrapping it in a warm damp cloth. Once thawed, reset the boiler.
- Reset the boiler DIY safe
Press and hold the reset button (often marked with a flame symbol or the word RESET) for around three seconds, then release. The boiler should attempt to start. If it fires up and runs normally, monitor it over the next day or two. If it locks out again with the same code, do not keep resetting — repeated failed ignitions can be unsafe and will not cure the underlying fault.
- Check that the flue terminal is clear DIY safe
From outside (ground level only — do not climb ladders), visually inspect the flue outlet on the exterior wall or roof. Check for obvious blockages such as bird nests, leaves, or debris around the terminal grille. Do not attempt to dismantle any part of the flue; if you suspect an internal blockage, this must be investigated by a Gas Safe engineer.
- Call a Gas Safe registered engineer Gas Safe engineer
If the boiler will not light after the checks above, or if it relights but keeps returning to 1P5 / 5P1, you need a Gas Safe registered engineer. They will test gas pressure at the appliance, inspect and clean or replace the ignition and ionisation electrodes, check the gas valve electrically, and inspect the flue for partial blockages. Do not continue resetting a boiler that repeatedly fails to ignite.
Parts you may need
- Ignition / ionisation electrode assembly · from £35
- Ignition lead and HT connector · from £20
- Gas valve · from £120
- PCB (control 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
Is 1P5 the same as 5P1 on a Chaffoteaux boiler?
Almost certainly yes. Chaffoteaux's segmented LED displays can make the digit '5' look like the letter 'S', and the code sequence can appear reversed depending on how the segments are lit. The registered code in Chaffoteaux's technical database is 5P1 (followed by 5P2 and 5P3 for repeated ignition failures), and 1P5 is the most common misreading of it. Both refer to a failed ignition attempt. If you are unsure, check your boiler's installation manual or photograph the display and compare it with the manual's fault-code table.
Can I fix the 1P5 / 5P1 fault myself?
The safe homeowner checks — confirming your gas supply is on, topping up boiler pressure, thawing a frozen condensate pipe, and performing a single reset — are worth trying first and cost nothing. However, if the boiler still won't light, the cause is almost always a faulty electrode, a gas pressure issue, or a failing gas valve, all of which must be diagnosed and repaired by a Gas Safe registered engineer. Do not repeatedly reset a boiler that keeps locking out.
How much does it cost to fix a Chaffoteaux ignition fault in the UK?
For the most common repair — cleaning or replacing the ignition electrode — expect to pay roughly £100–£150 including the engineer's labour. A gas valve replacement typically costs £180–£300 including parts and labour. For most homeowners the total bill falls somewhere between £120 and £350. PCB replacement is less common for this specific fault but can cost £250–£450 if needed; if your boiler is more than 10–12 years old, it may be worth getting a replacement quote alongside the repair estimate.
Why does my Chaffoteaux boiler show 5P1, then 5P2, then 5P3?
These three codes represent the boiler's three ignition attempts in sequence. When the boiler tries and fails to light the burner, it logs 5P1. If a reset is attempted and it fails again, it progresses to 5P2, and a third failure produces 5P3. Each code means the same underlying problem is unresolved. Once you see 5P2 or 5P3, stop resetting and call a Gas Safe engineer — the boiler is telling you it has already tried multiple times without success.