Chaffoteaux 511 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 511 fault code mean?
Fault code 511 on a Chaffoteaux boiler almost certainly represents a misread of either 5P1 or 501 — a well-known display quirk on older Chaffoteaux seven-segment screens, where the letter 'P' can look like '1', turning '5P1' into '511'. All three codes belong to the same ignition-lockout family. The boiler has attempted to light the burner but failed to detect a stable flame, so it has locked out for safety. After three unsuccessful ignition attempts the unit shuts down completely, cutting both heating and hot water. Because this is a non-volatile lockout, the boiler will not attempt a restart on its own — a manual reset is required. On Urbia and Pigma models, the closely related 501 code carries the same meaning: a burner or ignition failure that the control system cannot resolve automatically.
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 valve closed Common
The most frequent trigger. If the gas isolation valve at the boiler has been accidentally turned off, or if there is a wider supply issue affecting your street or meter, the burner simply has no fuel to ignite. Always rule this out first before investigating anything else.
- Dirty or worn ignition / ionisation electrode Common
After several heating seasons, carbon deposits and oxidation build up on the electrode tip. The burner may actually light briefly, but the ionisation current — the tiny electrical signal the electrode uses to confirm a flame is present — becomes too weak for the control board to recognise, triggering an immediate lockout. This is especially common on Mira, Niagara, Inoa, and Urbia models that have not had a recent service.
- Frozen condensate pipe Common
In cold weather the plastic condensate drain pipe that runs to an outside wall can freeze solid, causing a back-pressure fault that prevents ignition. If you are seeing this code during or after a cold snap, a frozen condensate pipe is a very likely culprit.
- Low gas pressure at the appliance Sometimes
Natural gas supply pressure below roughly 17 mbar (dynamic) is enough to prevent reliable ignition. This can be caused by an ageing meter, a faulty regulator, or high demand on the local network. The boiler fires, fails to establish a stable flame, and locks out.
- Misaligned or incorrectly gapped electrode Sometimes
If the boiler has been recently serviced or stripped down, the ignition electrode may not have been refitted with the correct spark gap. Too wide a gap produces a weak, inconsistent spark that cannot reliably ignite the gas-air mixture.
- PCB or control board fault Rare
If all ignition components test correctly and gas pressure is adequate, the PCB itself may be failing to send the ignition signal or failing to read the ionisation feedback correctly. This is less common but becomes more likely on boilers over ten years old.
How to fix it
- Check your gas supply is on and working DIY safe
Go to the kitchen and try lighting a gas hob burner. If it lights normally, gas is reaching the property. Also check that the isolation valve on the gas pipe feeding the boiler (usually a quarter-turn lever near the appliance) is fully open — the slot in the lever should be in line with the pipe. If you suspect a broader gas supply issue, contact your gas supplier.
- Reset the boiler (once or twice only) DIY safe
Locate the reset button on the control panel — on most Chaffoteaux models it is labelled 'R' or 'Reset'. Press and hold it for approximately 5–10 seconds until the display changes. The boiler will run through its start-up sequence and attempt to relight. If it fires successfully, monitor it over the next hour. If the fault code returns, do not keep resetting — repeated resets without finding the cause can mask a more serious problem.
- Check and thaw a frozen condensate pipe (winter only) DIY safe
Look for a white plastic pipe (usually 21.5 mm or 32 mm diameter) exiting through an outside wall, typically terminating close to a drain. If it feels solid or has visible ice around it, gently pour warm — not boiling — water along its length until you hear the blockage clear. Then reset the boiler. Lagging the pipe afterwards will help prevent a recurrence.
- Check system water pressure DIY safe
Look at the pressure gauge on the boiler. Most Chaffoteaux combi boilers should show between 1.0 and 1.5 bar when cold. If it reads below 0.8 bar, top up via the filling loop (refer to your boiler's user guide for its location) until the gauge reads around 1.2 bar, then reset. Note that low pressure alone rarely causes a 511/5P1 ignition fault, but it is worth confirming before calling an engineer.
- Call a Gas Safe registered engineer if the fault persists Gas Safe engineer
If the boiler locks out again after one or two resets, or if none of the above checks resolve the issue, you need a qualified Gas Safe registered engineer. They will inspect and test the ignition and ionisation electrodes (cleaning or replacing them as needed), verify gas pressure and valve operation at the appliance, check electrode alignment and wiring condition, and assess the PCB if all other components prove serviceable. Do not attempt to adjust gas components, the electrode, or the control board yourself.
Parts you may need
- Ignition / ionisation electrode assembly · from £35
- Ignition lead and HT cable set · from £25
- Gas valve · from £120
- PCB (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 fault code 511 the same as 5P1 or 501 on a Chaffoteaux boiler?
Almost certainly yes. Older Chaffoteaux boilers use seven-segment displays that can render the letter 'P' in a way that looks identical to the digit '1', so what the boiler is actually showing as '5P1' gets misread as '511'. The 501 code on Urbia and Pigma models sits in the same ignition-failure family. All three point to the same root cause: the boiler cannot detect a stable flame and has locked out for safety. If you are unsure which code your boiler is genuinely showing, cross-reference with your model's manual or photograph the display and share it with your engineer.
Can I fix a Chaffoteaux 511 fault myself?
You can safely carry out a few checks yourself: confirm your gas supply is on, attempt one or two resets, thaw a frozen condensate pipe in winter, and verify system pressure is in the 1.0–1.5 bar range. Beyond that, the most common repair — cleaning or replacing the ignition and ionisation electrode — requires the boiler to be partially disassembled and the work to be verified by a Gas Safe registered engineer. Any work involving gas components, such as testing or replacing the gas valve, must be done by a Gas Safe engineer by law.
How much does it cost to fix a Chaffoteaux ignition lockout fault in the UK?
For the most common repairs — cleaning or replacing the ignition electrode and lead, or a straightforward gas valve test — most homeowners pay between £120 and £350 including parts, labour, and VAT. If the PCB turns out to be at fault, costs can rise to £400–£550 or more depending on the model and your location. Labour rates typically run from £60 to £100 per hour across the UK, with London and the South East at the higher end. If your Chaffoteaux boiler is over 12–15 years old and needs a major component, it may be worth getting a new boiler quote alongside the repair estimate.
Why does my Chaffoteaux boiler keep locking out with a 511 fault even after I reset it?
Repeated lockouts almost always mean the underlying cause has not been addressed — a reset only clears the fault flag, it does not fix the problem. The most likely culprits for recurring lockouts are a permanently dirty or degraded ionisation electrode (so the boiler lights briefly but immediately decides no flame is present), persistently low gas pressure, or in winter an ongoing condensate freeze. If your boiler relocks within a short time of resetting, stop resetting it and call a Gas Safe registered engineer so the root cause can be properly diagnosed.