Boiler
122
Error code 122 on a Potterton boiler indicates a low water pressure fault — one of the most common boiler problems in UK homes and straightforward to address if caught early. Left unresolved, it will lock out your boiler and leave you without heating or hot water.
What does this error mean?
Your Potterton boiler continuously monitors the water pressure inside the central heating system via a pressure sensor. When that pressure drops below approximately 0.5 bar, the boiler triggers error code 122 and shuts down as a safety measure. This prevents the heat exchanger from running dry and sustaining expensive damage.
Est. repair cost
£80–£250 for a Gas Safe engineer call-out and repair (e.g. PRV replacement or pressure sensor); repressurise only = free DIY
🔍 Likely causes
🛠️ Step-by-step fix
Check the pressure gauge on the boiler front panel. If it reads below 1 bar, low pressure is confirmed as the cause.
Repressurise the system using the filling loop — a flexible silver braided hose usually located beneath the boiler. Open both valves slowly until the gauge reaches 1.2–1.5 bar, then close both valves tightly.
Once repressurised, press and hold the reset button on your Potterton boiler (typically 3–5 seconds) to clear the error code and restart the boiler.
Monitor the pressure gauge over the next 24–48 hours. If pressure holds steady, the issue was likely a one-off drop or air in the system after bleeding radiators.
Visually inspect all visible pipework, radiator valves, and the area beneath the boiler for any damp patches, drips, or signs of a slow leak — do not attempt to repair gas connections yourself.
If pressure keeps dropping, or you cannot locate the filling loop, stop here and call a Gas Safe registered engineer — do not repeatedly repressurise without finding the root cause.
📞 When to call a professional
Call a Gas Safe registered engineer immediately if the pressure drops repeatedly within a few days of repressurising, if you can see an active water leak anywhere on the system, or if the error persists after a successful repressurise and reset. Tell the engineer: ‘My Potterton boiler is showing error code 122, I’ve repressurised the system but pressure keeps dropping’ — this gives them a clear starting point.
⚖️ Repair or replace?
A Gas Safe engineer can diagnose and fix most pressure-related faults — repairing a leaking PRV, fixing a pipe joint, or replacing a faulty pressure sensor — for between £80 and £250 depending on the part and labour time. If your Potterton boiler is over 10–12 years old and repair costs exceed £400, replacement with a modern A-rated combi boiler (typically £1,800–£3,000 installed) is usually the smarter long-term investment. For a boiler under 8 years old, repair is almost always the right call.