Boiler
117
Error code 117 on a Potterton boiler indicates a fault with the central heating pump or water circulation — it’s a moderately serious fault that will lock out your boiler and stop heating and hot water until it’s resolved.
What does this error mean?
The 117 code tells you the boiler’s internal controls have detected that water isn’t circulating properly through the system. Potterton boilers monitor flow and return temperatures; if the difference between them is too large, or flow is too slow, the boiler interprets this as a pump or circulation failure and shuts down for safety. Left unresolved, running a boiler with poor circulation can cause overheating and damage to the heat exchanger.
Est. repair cost
£150–£350 for pump replacement; £300–£600 for a full power flush; PCB replacement £200–£400
🔍 Likely causes
🛠️ Step-by-step fix
Reset the boiler: Press and hold the reset button (usually marked with a flame and cross symbol) for 3–5 seconds. If the boiler fires up and runs without returning code 117, monitor it closely for 24 hours.
Check all heating valves are open: Locate the lockshield and thermostatic radiator valves (TRVs) throughout your home and ensure none are fully closed, as this restricts system flow.
Bleed your radiators: Starting from the ground floor and working upward, use a radiator key to release trapped air. If a lot of air escapes, this may be contributing to the circulation fault.
Listen to the pump: The pump is usually located near the boiler — a humming with no water movement suggests a seized pump, while total silence may indicate a power or PCB issue. Do not attempt to open or repair the pump yourself.
Check your system pressure: Look at the pressure gauge on the boiler front panel. It should read 1–1.5 bar when cold. If it’s below 0.5 bar, repressurise via the filling loop (refer to your boiler manual). Low pressure worsens circulation.
If the fault persists after the steps above, stop here — this is now a job for a Gas Safe registered engineer. Do not attempt to dismantle the pump, valves, or any gas components.
📞 When to call a professional
If the boiler locks out again within a short time after a reset, or if you suspect the pump is seized, sludged up, or the PCB is faulty, call a Gas Safe registered engineer immediately — do not attempt further DIY. When you call, tell them your boiler model (e.g. Potterton Assure, Titanium, or Gold), that you’re seeing error code 117, and whether the pump makes any noise. This helps them arrive with the right parts.
⚖️ Repair or replace?
A pump replacement on a Potterton boiler typically costs £150–£350 including parts and labour in the UK; a power flush to clear sludge runs £300–£600 depending on system size. If your boiler is over 10–12 years old and has a history of faults, replacement with a new A-rated combi (typically £1,800–£3,000 installed) is often better value long-term than repeated repairs. For boilers under 8 years old in otherwise good condition, repair is almost always the right call.