Error E110

Safety first:

1. If you smell gas, get everyone out of the building immediately and call the gas emergency number. Do not attempt any checks.

2. Turn the boiler off at the mains and allow it to cool before touching any external pipework or radiators.

3. Do not remove the boiler casing or attempt internal electrical or gas work unless you are a Gas Safe registered engineer.

Initial checks a homeowner can do:

1. Note the exact error display and any other symptoms (no hot water, no heating, noises, leaks).

2. Allow the boiler to cool for 10–20 minutes, then try a boiler reset following the manufacturer’s instructions. If the code does not clear or returns immediately, stop and proceed with checks below.

3. Check the system pressure gauge when the boiler is cold. The normal range is about 1.0–1.5 bar. If pressure is below 1.0 bar, you can top up the system using the filling loop until the pressure is in the correct range, then close the filling valves.

4. Bleed radiators to remove trapped air. Work around the house, opening bleed valves until a steady stream of water appears and re-check system pressure (bleeding can reduce pressure).

5. Check visible pipework and radiator valves are open (including any external isolation/bulkhead valves) and look for leaks in the system which will cause pressure loss.

Further diagnostic and specific fixes (when to try them and what they show):

1. Pump check (homeowner): With the boiler powered on and a demand for heating/hot water, listen for the pump running (a low hum) and feel the pump housing carefully through insulation—if the pump is stone cold and the boiler is trying to run, the pump may not be operating. Do not remove covers. If the pump appears seized or not running, call an engineer.

2. After topping up pressure and bleeding, try restarting the boiler. If E110 clears and the system operates normally, monitor pressure and performance. If E110 returns, do not repeatedly reset; note frequency and conditions and call an engineer.

3. If the boiler was running constantly before E110 or the pump was running to try to cool the boiler, this can indicate the overheat thermostat is open (faulty) or there is persistent poor circulation or blockages. These are engineer-level diagnoses.

4. Do not attempt continuity or resistance checks on sensors or overheat thermostats unless you are qualified. A common engineer diagnosis is to check continuity across the overheat thermostat and the NTC/flow sensors, inspect the heat exchanger for blockage, inspect the diverter valve and motor, and verify pump performance and wiring.

When to call a professional and what they will do:

1. Call a Gas Safe registered engineer if the error persists after cooling, resetting, topping up pressure and bleeding radiators, or if you suspect pump failure, blocked heat exchanger, faulty overheat thermostat or temperature sensor, or any leak.

2. An engineer will safely remove the boiler casing, check continuity of the overheat thermostat, test and replace faulty sensors or thermostats, verify pump operation and wiring, check the diverter valve and motor, inspect the heat exchanger for blockages or scale, and test system flow/return temperatures. They will also check gas and combustion where relevant.

3. If the overheat thermostat has tripped but is not resetting, the engineer may replace the thermostat(s). If circulation faults are found they may clear blockages, replace or service the pump or diverter, or recommend further system work (e.g. powerflush or fitting a magnetic filter).

Final notes:

- E110 is a protective shutdown; do not force the boiler to run.

- Simple homeowner actions: allow to cool, reset once, check and top up pressure, bleed radiators, ensure valves are open.

- For any internal component testing, repairs, or if faults persist, always use a Gas Safe registered engineer for safety and warranty reasons.