Error 2 red flashes

Safety first

1) If you smell gas: get everyone out, do not operate electrical switches, call your gas emergency number immediately. 2) If the boiler is hot, allow it to cool for at least 20–30 minutes before touching controls. 3) Do not open the boiler casing or attempt internal repairs; only perform external/basic checks described below. 4) Do not keep repeatedly resetting the boiler if the fault returns — this can cause further damage.

Initial homeowner checks

1) Note the fault (2 red flashes), time and any circumstances (e.g. after bleeding radiators, after a power cut). This helps the engineer. 2) Check the pressure gauge on the boiler: normal range is about 1.0–1.5 bar for a cold system (up to 2–3 bar when hot). If the pressure is well below 1.0 bar top up the system; if it is above 3 bar you should not top up — bleed a radiator to reduce pressure and call an engineer if it repeatedly goes high. 3) Check that all radiator TRVs and lockshield valves are open so water can flow. 4) Check for obvious leaks in the system (visible pipes, radiators, valves) and any water on the floor. 5) Inspect external flue/vent terminal for blockage (birds’ nests, leaves, snow); clear only external obstructions you can safely remove.

How to top up system pressure (only if you are comfortable doing so)

1) Locate the filling loop (flexible braided hose or fixed valve assembly beneath the boiler). It usually has two valves or a single lever. 2) With the boiler off, open the filling loop valves slowly until the pressure gauge rises to about 1.0–1.5 bar. Watch the gauge and close both valves fully once in range. 3) If the filling loop is removable, ensure it is correctly secured or removed per the installer’s instructions. 4) Check for leaks after topping up. If you are unsure how to do this, stop and call an engineer.

Bleeding radiators to remove air (may restore circulation)

1) Turn off the boiler and central heating and let the system cool. 2) Starting at the lowest radiator, use a radiator key to open the bleed valve until water (not air) appears, then close. Have a cloth and container ready. 3) Repeat for other radiators, then re-check system pressure and top up if the pressure has dropped below 1.0 bar. 4) Restart the boiler and see if the fault clears.

Reset procedure

1) After cooling and performing the checks above, try a single reset: press and hold the boiler reset button (or turn the selector to R if your model uses that) for 5–10 seconds. 2) Allow the boiler to attempt to restart. If it runs normally and the heating/hot water returns, monitor the system closely for recurrence. 3) Do not perform repeated resets if the same fault returns.

If the problem persists or you find any of the following, call a Gas Safe registered engineer

1) The boiler locks out again with 2 red flashes after reset. 2) You have low or fluctuating pressure that won’t stay stable after topping up. 3) The pump appears to be seized (boiler attempts to fire but radiators stay cold, you hear no pump noise or a loud noise). 4) There are signs of a leak, severe scale/blockage or a suspected heat-exchanger fault, or you have electrical/PCB/sensor related behaviour. 5) You smell gas.

When you call an engineer, give them the boiler model, the exact fault (2 red flashes / over-temperature lockout), what checks you have already done (pressure, bleeding radiators, filling loop) and whether the fault is intermittent or constant. A professional will safely inspect the circulation pump, expansion vessel and pressure controls, check for blockages/scale in the heat exchanger, verify sensor operation and PCB status, and carry out any repairs or parts replacement that are required.