Error 1 red flash

Safety precautions:

- If you smell gas, evacuate the property immediately and call your gas emergency number—do not try to operate or reset the boiler.

- If there is a significant water leak or visible electrical arcing, switch the boiler and mains electricity off and isolate water if safe to do so; call an engineer.

- Do not remove the boiler cover or attempt to replace sensors, gas components, or internal wiring unless you are a Gas Safe registered engineer.

Initial checks a homeowner can do:

1) Note the boiler model, serial number and exact fault indication (1 red flash) and any other display messages. Take photos if possible.

2) Check the system pressure on the gauge: ideal central heating pressure is about 1.0–1.5 bar when cold. If it is below about 1 bar, the boiler may not circulate properly.

3) Look and listen for obvious signs: are any radiators cold at the top (airlock)? Is the pump making a humming sound (indicating it’s trying to run)? Is there visible water around the boiler or pipes? Is the outside flue terminal clear of debris, birds’ nests or snow?

4) In cold weather check the condensate discharge pipe (usually at the front/bottom of the boiler) for freezing; a blocked condensate will cause faults.

Basic remedial actions you can try:

1) Top up system pressure if low: locate the filling loop (a braided silver hose beneath the boiler or separate filling valves), open the valves slowly while watching the pressure gauge until it reaches about 1.0–1.5 bar, then close the valves. Only do this if you are confident and the filling loop is intact and correctly fitted.

2) Bleed radiators to remove trapped air: start with the radiators nearest the boiler and use a radiator key to release air until water flows, then re-check pressure and top up if needed.

3) If you suspect a frozen condensate pipe, thaw gently using warm (not boiling) water or a hot water bottle applied externally to the plastic pipe; do not use naked flames or excessive heat.

4) Check that radiator TRVs and any isolation valves at the boiler are open.

5) Reset the boiler once after carrying out the above checks: press and hold the reset button (or turn the selector to R as per your model) for about 5–10 seconds, then allow the boiler to attempt a restart. Do not keep resetting repeatedly; one or two attempts after checks is acceptable.

How to interpret results and next steps:

- If topping up pressure, bleeding radiators, clearing a frozen condensate and a single reset clears the fault and the boiler runs normally, monitor the system. If pressure falls again or the fault returns, call an engineer.

- If the pump does not run (no noise or vibration when CH demand is present) or if flow and return pipes show a very large temperature difference (hot flow, much cooler return), that indicates poor circulation, possible pump seizure or severe airlock and you should call a Gas Safe engineer—do not try to strip the pump yourself.

- If pressure and circulation look normal but the 1 red flash persists after a proper reset, that strongly suggests a faulty sensor (flow/return NTC), wiring, or an internal PCB or thermistor issue; these parts should be diagnosed and repaired by a Gas Safe registered engineer.

When to call a professional (Gas Safe engineer):

- The fault persists after the basic checks and a proper reset.

- System pressure will not stay up or you see active leaks.

- The pump appears seized or does not run.

- You see water on or around the PCB or internal components.

- You smell gas or suspect a gas supply fault.

- You are uncomfortable performing any of the checks above.

What to provide to the engineer: your boiler model and serial, description of the fault, what checks you performed (pressure topped up, radiators bled, condensate thawed, reset attempts), and any photos of the fault light or wet areas. This helps speed diagnosis. Avoid attempting internal electrical or gas repairs yourself; sensor, pump and PCB replacements require specialist skills and certification.