Error 110

Safety first

1) If you smell gas, leave the property immediately and call the gas emergency number. Do not operate the boiler. 2) If there are hot surfaces or steam, allow the boiler and system to cool before touching anything. 3) Do not open the boiler casing, do any work on gas or electrical parts, or bypass safety devices. Only a Gas Safe engineer should carry out internal repairs.

Initial homeowner checks (safe, non-intrusive)

1) Note any accompanying symptoms: is the heating off, are radiators cold, is there water visible around the boiler, or any unusual noises from the pump or pipes? 2) Check the boiler display: try a single reset using the boiler controls as described in your manual. Wait at least 20–30 minutes after shutdown and cooling before resetting. If the code cleared but returns, do not keep resetting. 3) Check the system pressure gauge. Normal pressure is usually around 1–2 bar when cold. If pressure is very low or very high, follow your manual to repressurise or isolate and call an engineer. 4) Check radiators: if some are cold at the bottom there may be an airlock — bleed a radiator using the bleed valve (wear gloves and have a cloth). 5) Check external controls and thermostat settings and the room thermostat batteries/clock/timers to ensure the boiler is being asked to run normally.

Further diagnostic checks you can safely do

1) Listen for the pump when the heating is calling: you may hear or feel the pump run. Lack of pump noise when the boiler is demanding heat can indicate a circulation issue. 2) If you have basic DIY confidence, you can check for any obvious visible leaks or discharges from the pressure relief pipe or connections. If you find active leaks turn the boiler off and call an engineer. 3) If you live in a very hard water area and the boiler is older, consider whether scale buildup or a blocked heat exchanger could be present; this is not something to attempt to dismantle yourself but is a common cause of overheating and will need a professional descaling or replacement.

What to avoid

1) Do not repeatedly reset the boiler to clear the fault; multiple resets can cause the boiler to lock out and will not fix the underlying issue. 2) Do not open the boiler case or touch wiring, gas valves, or the burner. 3) Do not attempt to replace sensors or PCB components unless you are a qualified engineer.

When to call a professional

1) If the fault does not clear after the simple safe checks above, or if you suspect pump failure, blocked flow, a leaking component, or a faulty temperature sensor, call a Gas Safe registered heating engineer. 2) Tell the engineer the exact fault code 110, the steps you have already tried, any noises, visible leaks, pressure readings and whether the boiler reset temporarily. 3) The engineer will carry out safe electrical and sensor checks, measure probe continuity and temperatures, test/replace the send (flow) probe if faulty, inspect and test the pump, diverter and flow components, and check the heat exchanger for blockages or scale; they will also check PCB inputs and safety devices. 4) If the cause is a damaged temperature probe, replacement and calibration should be performed by the engineer. If the cause is true overheating due to circulation failure or blockage, the engineer will correct the circulation fault and verify the safe operation of the boiler.

Final notes

This fault is a safety shutdown and should not be ignored. If you are not confident performing the safe, non-intrusive checks listed above, or if the error persists, stop attempting further repairs and book a Gas Safe engineer to diagnose and repair the boiler.