Error 153

Safety first: If you smell gas, evacuate the property immediately, shut off the gas supply at the meter if it is safe to do so, and call the gas emergency line. If there are signs of water leaks, electrical burning, or the boiler will not switch off, isolate the electrical supply to the boiler at the consumer unit and call a professional. Do not attempt internal repairs on gas or sealed components unless you are a Gas Safe registered engineer.

Initial checks a homeowner can do:

1) Note what happened and when: record the error 153, what the boiler display shows, whether central heating or hot water was being called for, and any noisy, odour, or leak symptoms. This helps the engineer later.

2) Check whether other gas appliances work to confirm the gas supply and check the meter and any external isolation valves are open. If multiple appliances have no gas, contact your gas supplier.

3) Check boiler pressure on the gauge—ideal cold reading is typically around 1.0–1.5 bar. If low (below about 0.7–0.8 bar), this can cause faults and you may need to repressurise using the filling loop (consult your manual).

4) Inspect the external condensate pipe (if fitted) on cold weather — if frozen it can cause lockouts. If frozen, thaw with warm (not boiling) water and insulate/lag the pipe.

5) Check the flue terminal for obvious blockages (birds’ nests, leaves) and clear any light debris from outside, keeping safe distance from the flue when the boiler is running.

6) Check thermostat/timer controls and room stat batteries; ensure they are calling for heat correctly.

Specific reset and diagnostic steps:

1) Attempt a controlled reset following your model’s method: press and hold the reset button for the time recommended by Baxi (typically a few seconds), or turn the selector to R and hold for 3–5 seconds, or turn the thermostat knob fully anticlockwise and hold until the red lockout light goes out, then return to normal setting. Observe the panel: the red lockout light should go out and the burner indicator should come on if the boiler relights.

2) After reset, give the boiler a few minutes to go through its start sequence. Watch for the burner light and rising temperature. If it restarts and runs normally, monitor for recurrence over the next 24–48 hours.

3) If the boiler refuses to reset or immediately returns to lockout with the same or a different code, do not attempt further resets. Note any additional error codes or indicator lamp sequences and the exact behavior (number of attempts to ignite, smells, noises).

4) If pressure is low, repressurise to the correct range using the filling loop per the handbook. If pressure repeatedly drops, that indicates a leak or component failure and needs an engineer.

5) If you suspect a frozen condensate pipe, thaw it and then try a reset. If the condensate is blocked for other reasons (debris, domestic wastewater ingress), an engineer should clear or replace it.

6) If the reset clears the fault but the boiler locks out again during or after running, do not continue to reset repeatedly. Repeated forced resets can override safety actions and mask the underlying problem.

When to call a professional (and what to tell them):

- Call a Gas Safe registered engineer if the 153 code returns repeatedly or the boiler will not stay running after reset. Also call an engineer immediately if you smell gas, see water leaks, hear unusual banging or persistent fan noise, or if other error codes appear.

- Tell the engineer the exact error (153 "Forced reset unit unlocked"), what you observed, any other displayed codes or lights, whether you attempted a reset and what happened, the boiler pressure reading, and whether you have already checked condensate, flue or gas supply.

Final note: Error 153 often signifies a previously cleared lockout rather than a single specific fault – it clears transient issues but flags potential repeat problems. For safety and warranty reasons, any internal gas, ignition, or PCB work must be done by a Gas Safe registered engineer. If the error is a one-off and the boiler runs normally after a proper reset, monitor it closely; if it recurs, arrange a professional inspection.