Boiler
133
Error code 133 on a Potterton boiler indicates an ignition fault — the boiler has attempted to light but failed to detect a flame. It’s a common fault but not one to ignore, as your boiler will lock out and stop producing heat or hot water until it’s resolved.
What does this error mean?
The 133 code means the boiler’s control board sent a signal to ignite the burner, but the flame sensor (also called the ionisation probe) either detected no flame at all, or the flame appeared and then cut out immediately. Potterton boilers are designed to lock out after a failed ignition attempt as a safety measure to prevent unburnt gas from accumulating. The boiler won’t restart automatically — it needs either a manual reset or an engineer to investigate the root cause.
Est. repair cost
£80–£250 for a Gas Safe engineer callout and repair (parts dependent); no DIY repair applicable for this fault
🔍 Likely causes
🛠️ Step-by-step fix
Step 1 — Reset the boiler: Locate the reset button (usually a flame symbol on the front panel). Hold it for 3–5 seconds. The boiler will attempt to re-ignite. If it fires up successfully and runs normally, monitor it over the next 24 hours.
Step 2 — Check your gas supply: Try lighting a gas hob or another gas appliance. If those also fail, contact your gas supplier — there may be a local supply interruption. Do not attempt any further boiler work.
Step 3 — Check the condensate pipe (in freezing weather): If temperatures are below zero, the external condensate pipe may be frozen. You can pour warm (not boiling) water over the plastic pipe where it exits the property to thaw it, then reset the boiler.
Step 4 — Check boiler pressure: Low pressure (below 1 bar on the gauge) can prevent ignition. If it reads below 1 bar, top up via the filling loop following your boiler’s manual instructions. Repressurise to around 1.2–1.5 bar, then reset.
Step 5 — If the fault persists after a reset, stop here. Do not attempt to open the boiler casing, adjust the gas valve, or clean the ignition components yourself. This is a gas appliance and further investigation must be carried out by a Gas Safe registered engineer.
📞 When to call a professional
If the boiler locks out again within a few hours of a successful reset, or if it fails to light at all after a reset, call a Gas Safe registered engineer immediately — do not keep attempting resets, as this can flood the heat exchanger. Tell the engineer the exact error code (133), how many times you’ve reset it, and whether the fault appeared suddenly or has been intermittent. A qualified engineer will inspect the ignition electrode, flame sensor, gas valve, and PCB.
⚖️ Repair or replace?
A professional repair for a 133 fault typically costs £80–£250 depending on the faulty component — a flame sensor or electrode is at the lower end, while a gas valve or PCB replacement sits at the higher end. If your Potterton boiler is over 10–12 years old and this is not its first significant fault, replacement is worth serious consideration; a new A-rated combi boiler costs £1,500–£2,500 fully installed but will be more efficient and reliable. For a boiler under 8 years old in otherwise good condition, repair is almost always the better value option.