Error E110

Safety first

1. If the boiler is showing E110, do not try to force it to run. Turn the boiler off at the mains isolator and allow it to cool before touching anything. Do not attempt any gas work or internal electrical repairs yourself. If you smell gas, leave the property immediately and call the emergency gas number.

Initial homeowner checks (safe, simple steps)

1. Reset the boiler following the manual instructions after it has fully cooled. Note whether the fault returns immediately or after a restart. A single, transient fault cleared by reset is different to a persistent fault.

2. Check the system pressure on the boiler gauge. If pressure is below about 1.0 bar, the system may not circulate correctly. If low, top up using the filling loop until pressure reaches about 1.0–1.5 bar, then close the filling loop valves. Consult the handbook for the exact filling procedure and location of the filling loop. Re-check the gauge after a short run.

3. Bleed radiators to remove trapped air. Use a radiator key, have a cloth and small container ready, open the bleed valve until water flows steadily, then close. Start with radiators on the highest floor and work downwards, or start with the radiator furthest from the boiler, to help expel airlocks. After bleeding, re-check system pressure and top up if needed.

4. Look and listen for obvious signs of pump operation. With the boiler on and there is a heating demand, you should hear or feel the pump running (a faint hum and vibration on the pump or pipework). Also check that radiator thermostatic valves are open and that any isolation valves near the boiler are open. If pipework near the boiler stays cold when the boiler is firing, that indicates poor circulation.

Specific diagnostic and next steps

1. If the problem persists after reset, correct pressure and bleeding, allow the boiler to cool and then try running again to observe behavior. Note any noises such as banging, gurgling or a loud humming pump sound and whether the E110 returns immediately or after a few minutes.

2. Do not attempt electrical continuity checks or sensor replacements yourself unless you are a competent electrician and have isolated the boiler and followed safe isolation procedures. Testing the safety overheat thermostat or NTC sensors requires removing covers and using a multimeter on isolated equipment; this is work for a Gas Safe engineer.

3. If you suspect the pump is seized (no hum, no flow and radiators remain cold), avoid forcing or disassembling the pump. Some pumps can be freed by an engineer who will isolate power and water, remove the pump if required, and either service or replace it.

4. If you suspect a blocked heat exchanger, a blocked condensate or drain, or scale build-up, call a professional. These faults require specialist cleaning or component replacement.

5. If you suspect a gas supply problem or any leak, stop using the appliance and contact your gas supplier or a Gas Safe engineer immediately.

When to call a professional

1. Call a Gas Safe registered engineer if the E110 code persists after the simple checks above, if you cannot identify circulation problems, if you find leaks, if the pump appears faulty, if the safety thermostat has operated, or if any internal sensors or wiring could be at fault. The engineer will safely isolate the boiler, test components such as the safety thermostat and NTC sensors, check pump and diverter operation, inspect the heat exchanger and hydraulics, and carry out any replacement or repairs required.

Remember: E110 is a safety shutdown for overheating. It is fine to try basic checks like reset, pressure top-up and radiator bleeding, but do not attempt internal boiler repairs, electrical tests, or gas work yourself. Persistent or unclear faults must be resolved by a Gas Safe registered engineer to ensure safety and proper repair.