Error No central heating

Safety precautions:

- If you smell gas, leave the building immediately, do not operate switches or electrical equipment, and call the gas emergency number. Do not attempt any repairs.

- Do not open the boiler casing or touch internal components. Live electrical and gas parts inside the boiler are dangerous. If in doubt, call a Gas Safe engineer.

- When working near hot pipes or radiators use gloves; parts may be hot.

Initial checks a homeowner can do:

1. Note any display or fault code on the boiler display. Photograph or write it down — engineers will need this.

2. Check the thermostat and programmer: ensure the central heating is programmed on, the room thermostat is set higher than room temperature, and any schedule or holiday mode is not active.

3. Confirm radiator valves are open on a couple of radiators (turn TRVs fully open for test). Check any bypass or lockshield valves are not closed.

4. Check the boiler pressure gauge when the system is cold. Target cold pressure is usually about 1.0–1.5 bar (check your manual). If pressure is low (below ~1.0 bar) the boiler may refuse to run central heating.

5. Check if domestic hot water still works. If hot water is OK but radiators stay cold, suspect circulation/zone valve/pump rather than a gas ignition fault.

Simple homeowner fixes and diagnostics:

1. Reset the boiler: press the RESTART button or turn the boiler off at the isolator for 30 seconds and turn back on. If the fault clears and stays cleared, monitor the system. If the same fault returns, note the code.

2. Re-pressurise the system (only if you are comfortable doing so and your boiler manual explains the filling loop):

- Locate the filling loop and its isolating valves. Open slowly until the pressure rises to about 1.0–1.5 bar, then close the valves.

- Close the filling loop and secure it if the loop is removable. Press RESTART on the boiler.

- If pressure repeatedly drops after topping up, do not keep adding water; call an engineer to find a leak or faulty expansion vessel.

3. Bleed radiators to remove trapped air, beginning with the highest radiator. After bleeding, re-check pressure and re-pressurise if needed.

4. Observe the boiler when central heating is called:

- Listen for the pump running (quiet hum) and feel the flow and return pipe temperatures carefully (use caution — pipes may be hot). If the boiler fires but pump is not running and pipes stay cool, pump or wiring to pump may be faulty.

- If the boiler fires but radiators remain cold and water temperature at the boiler flow is hot, the issue is likely circulation (pump, airlock, motorised zone valve, or closed isolation valve).

5. Check isolation/flow valves at the boiler are open (flow and return ball valves). If these are closed, open them.

6. If the boiler shows codes like F1 (low pressure), follow the repressurising step above. For codes such as F2, L2 (flame loss/ignition lockout) check other gas appliances and gas supply; reset once only and if it persists call Gas Safe. For thermistor (F4/F5), fan (F3) or PCB codes (F9/L9 etc) record the code and contact an engineer.

7. Check motorised zone valves and wiring visually if accessible: when you call for heating the valve head should move. If the valve is stuck in the hot water position or neither fully opens nor closes, this can stop central heating. Do not dismantle the valve; note its behaviour for the engineer.

8. Inspect the condensate pipe in freezing weather (if ignition/lockout codes relate to condensate blockage). A frozen or blocked condensate can cause ignition lockouts. Thawing a frozen condensate drain with warm (not boiling) water may help but if you are unsure call an engineer.

When to call a professional (Gas Safe registered engineer):

- Any gas-smell or suspected gas leak.

- Persistent fault codes after reset, especially flame loss/ignition (F2/L2), PCB errors (F9/L9), pump/fan failure (F3), thermistor faults (F4/F5/L4/L5), or low mains voltage warnings (F7).

- You cannot safely repressurise the system or pressure keeps dropping.

- The pump appears seized or needs replacement, a motorised valve is stuck, or electrical wiring or internal boiler components need inspection.

- Repeated lockouts, overheating (L1), or any internal component replacement or fault diagnostics.

What to tell the engineer: provide the boiler model, serial number if available, the exact fault code(s) displayed, whether hot water is working, boiler pressure reading, and a brief summary of checks you have already performed. Arrange an annual service to reduce the chance of future failures.