Boiler
103
Error code 103 on a Potterton boiler indicates a flame or ignition fault — specifically, the boiler is either failing to ignite or is losing its flame shortly after lighting, which triggers a safety lockout. While it can feel alarming, especially on a cold morning, it is one of the more common boiler faults and is often resolvable by a Gas Safe registered engineer relatively quickly. In this guide, you’ll learn exactly what causes the 103 fault, what you can safely check yourself, and when — and who — to call for a proper fix.
What does this error mean?
The 103 error code on Potterton boilers (including popular models such as the Potterton Promax, Assure, and Gold series) signals an ignition failure or ‘no flame detected’ lockout. In plain terms: your boiler has tried to light itself, but either the burner didn’t ignite at all, or the flame lit briefly and then went out before the boiler’s internal sensor could confirm it was burning safely. When this happens, the boiler’s control board immediately shuts everything down as a safety precaution — this is called a lockout. The appliance is not broken beyond repair; it has simply refused to operate until the underlying fault is investigated. The component most directly involved is the flame detection electrode (sometimes called the ionisation probe), but the fault can also originate from the gas supply, the ignition electrode, the gas valve, or the PCB (printed circuit board). Until the cause is identified and resolved, the boiler will not restart on its own.
Est. repair cost
£80–£150 for a Gas Safe engineer call-out, diagnosis, and electrode clean or replacement. £200–£400 if the gas valve or PCB requires replacement (parts plus labour).
🔍 Likely causes
🛠️ Step-by-step fix
Step 1 — Check your gas supply first: Before touching the boiler, confirm your gas supply is working by turning on a gas hob burner (if you have one). If you have no gas at other appliances, contact your gas supplier immediately — this is a supply issue, not a boiler fault. If you’re on a prepayment meter, check your credit balance.
Step 2 — Check whether neighbours are affected: If you live in a terrace or flat and suspect a wider supply issue, quickly check with a neighbour. A street-level gas supply fault will affect multiple properties and must be reported to National Gas Emergency on 0800 111 999.
Step 3 — Perform a manual reset: Locate the reset button on your Potterton boiler — on most Promax and Assure models it is a clearly labelled button on the front panel, sometimes requiring you to hold it for 3–5 seconds. Press and hold the reset button as directed in your boiler’s manual, then wait 5–10 minutes to see if the boiler fires up successfully. Do not reset more than twice in quick succession.
Step 4 — Check the condensate pipe (in freezing weather only): If the outdoor temperature is below zero and your boiler has an external condensate pipe (the small white plastic pipe that exits through an outside wall), it may be frozen. You can safely thaw it by pouring warm (not boiling) water over the external section of the pipe. Once thawed, reset the boiler as in Step 3.
Step 5 — Check the boiler’s pressure gauge: Look at the pressure gauge on the front of the boiler. It should read between 1 and 1.5 bar when cold. If it reads below 0.5 bar, the system may need repressurising — consult your boiler manual for the correct repressurising procedure using the filling loop. Note: low water pressure alone is unlikely to cause a 103 code, but it can contribute to lockout behaviour.
Step 6 — Do not attempt any further DIY: If the boiler still shows the 103 error after a reset and the above checks, this is where all DIY must stop. The remaining causes — a dirty ionisation electrode, faulty ignition electrode, gas valve issue, low gas pressure, or PCB fault — all require a Gas Safe registered engineer to diagnose and repair safely. Working on gas components without Gas Safe registration is illegal and extremely dangerous.
Step 7 — Call a Gas Safe registered engineer: Contact a Gas Safe registered heating engineer and tell them your boiler model (e.g. Potterton Promax 24), the fault code displayed (103), how long the issue has been occurring, and what steps you have already tried (reset, checked gas supply, checked condensate). This information will help them prepare the right parts and diagnose the fault faster, potentially saving you money on call-out time.
📞 When to call a professional
You should call a Gas Safe registered engineer as your primary course of action the moment a reset and basic supply checks have failed to clear the 103 error. Do not attempt to open the boiler casing, touch the electrodes, adjust the gas valve, or interfere with any internal components — it is illegal to carry out gas work without Gas Safe registration, and doing so could put your household at serious risk of gas leak, explosion, or carbon monoxide poisoning. When you call, tell the engineer: ‘My Potterton [model name] is showing error code 103. I’ve checked the gas supply is working, I’ve reset the boiler twice, and the fault is still present.’ This gives them everything they need. If you smell gas at any point — even faintly — do not reset the boiler. Leave the property, leave doors open as you go, and call the National Gas Emergency Service on 0800 111 999 immediately.
⚖️ Repair or replace?
For most homeowners, a 103 fault is a repair job, not a replacement trigger — unless the boiler is already old or has a history of repeated faults. Here’s how to think about it: If your Potterton boiler is under 10 years old and this is its first significant fault, repair is almost always the right call. The most common fix — cleaning or replacing the ionisation electrode — is inexpensive and straightforward for an experienced engineer. If the fault turns out to be the PCB, costs rise considerably (£200–£400 for parts and labour), and on a boiler that is 10–15 years old, it is worth comparing that cost against a new boiler installation. A new Potterton or equivalent mid-range boiler installed by a Gas Safe engineer typically costs £1,500–£2,500 fully fitted. Potterton is owned by Baxi, and parts availability for current and recent models (Promax, Assure, Gold) is generally very good through UK heating merchants. For boilers over 15 years old with recurring faults, replacement becomes the more cost-effective and energy-efficient long-term decision, particularly given modern condensing boiler efficiency ratings.