Boiler
101
Error code 101 on a Potterton boiler indicates a fault with the appliance’s ignition system — specifically, the boiler is failing to detect a flame after attempting to light. It’s one of the more common fault codes on Potterton models including the Assure, Titanium, and Gold ranges, and while it can occasionally be resolved with a simple reset, it often points to an underlying issue that needs a Gas Safe registered engineer. In this guide, we’ll walk you through exactly what the code means, the most likely causes, what you can safely do yourself, and when it’s time to pick up the phone.
What does this error mean?
Error code 101 on a Potterton boiler is an ignition lockout fault. In plain English, this means your boiler has tried to light itself — typically one to three times — and failed to detect a stable flame. As a safety measure, the boiler locks itself out to prevent unburnt gas from building up inside your home. The component responsible for detecting the flame is called the flame sensor (or ionisation electrode). When the burner fires, this probe senses the electrical current produced by the flame. If it doesn’t detect that current within a set window of time, the boiler’s control board registers the 101 fault and shuts everything down. This is a protective mechanism, not a flaw — but it does mean something in the ignition chain isn’t working correctly and needs attention.
Est. repair cost
£90–£150 for a Gas Safe engineer call-out and flame sensor clean or electrode replacement; £180–£320 for a gas valve replacement (parts and labour); £250–£450 for a PCB replacement (parts and labour). Engineer call-out fees alone typically range from £60–£100 in the UK.
🔍 Likely causes
🛠️ Step-by-step fix
Step 1 — Check your gas supply first: Before doing anything with the boiler, check that other gas appliances in your home (such as your gas hob) are working normally. If they aren’t, the problem is with your gas supply, not the boiler. Contact your gas supplier or call the National Gas Emergency Service on 0800 111 999 immediately if you suspect a supply fault or smell gas.
Step 2 — Check your prepayment meter (if applicable): If you’re on a prepayment gas meter, confirm it has credit. A meter that’s run out is one of the most overlooked causes of ignition lockout faults. Top it up and then attempt a reset.
Step 3 — Check the gas isolation valve on the boiler: Locate the isolation valve on the gas pipe leading to your boiler — it’s usually a quarter-turn valve near the appliance. Ensure it’s fully open (handle parallel to the pipe). Never attempt to open valves on the main gas supply pipework.
Step 4 — Reset the boiler: Most Potterton boilers have a reset button on the front panel — on models like the Assure and Titanium, this is typically a dedicated button or a combination press-and-hold on the control dial. Hold the reset for 3–5 seconds as per your boiler’s manual. The boiler will attempt to re-ignite. Watch to see if it fires successfully or returns to the 101 fault.
Step 5 — Wait and reset again (once more only): If the first reset fails, wait five minutes and try once more. Attempting repeated resets beyond this is not recommended — if the fault persists after two reset attempts, continuing to force ignition attempts without identifying the cause is unsafe and can stress boiler components.
Step 6 — Check for a frozen condensate pipe (in cold weather): If the temperature outside is at or below freezing, your boiler’s condensate pipe — the white plastic pipe that exits through an external wall — may be frozen. You can safely thaw it by pouring warm (not boiling) water over the external section of the pipe, or wrapping a hot water bottle around it. Once thawed, reset the boiler. This applies where the 101 lockout has coincided with a cold snap.
Step 7 — Do not attempt further DIY: Beyond the steps above, all other causes of a 101 error code — including flame sensor cleaning, electrode replacement, gas valve inspection, and PCB diagnosis — involve working on gas components or internal boiler parts. These tasks must only be carried out by a Gas Safe registered engineer. Do not open the boiler casing or attempt to adjust any internal components.
📞 When to call a professional
You should call a Gas Safe registered engineer if: the boiler returns error code 101 after two reset attempts; the fault clears after a reset but keeps coming back over subsequent days; you have confirmed your gas supply is working but the boiler still won’t ignite; or you are in any doubt whatsoever. When you call, tell the engineer: ‘My Potterton boiler is showing fault code 101 — it’s going into ignition lockout. I’ve checked the gas supply is on, I’ve reset it twice, and it’s still locking out.’ This gives them the information they need to come prepared with likely parts. Do not attempt to use the boiler in lockout mode, and if you ever smell gas, leave the property, do not operate any electrical switches, and call the National Gas Emergency Service immediately on 0800 111 999.
⚖️ Repair or replace?
For most Potterton boiler owners, repair is the right call — provided the boiler is under 10 years old and has been reasonably well maintained. Potterton is part of the Baxi group, so parts availability is generally good across the UK, and most ignition-related faults are relatively straightforward for an experienced engineer to diagnose and fix in a single visit. If the fault is a dirty flame sensor or a failed ignition electrode, you’re looking at a relatively low-cost repair. A faulty gas valve is more expensive but still usually worth replacing on a boiler under 12 years old. If the PCB has failed and your boiler is over 10–12 years old, the maths starts to tip towards replacement — a new PCB on some Potterton models can cost £200–£350 in parts alone, and a boiler of that age may also have other components nearing end of life. A new A-rated combi boiler typically costs £1,500–£2,500 supply and installed, and will be significantly more energy-efficient, potentially saving you £200–£350 per year on gas bills depending on your current boiler’s efficiency rating. If your Potterton boiler is over 12 years old and has had repeated faults, replacement is strongly worth considering.