Error E125

Safety precautions:

1. If you smell gas, leave the building immediately and call your gas emergency number—do not attempt any checks. 2. Turn the boiler off and isolate the electrical supply before touching any controls. 3. Allow the boiler and system to cool before bleeding radiators or opening any valves. 4. Do not remove the boiler casing or attempt internal electrical or gas repairs—those must be done by a Gas Safe registered engineer.

Initial homeowner checks you can safely do:

1. Check system pressure on the boiler gauge. Normal cold pressure is usually around 1.0–1.5 bar on Baxi boilers. If it is below about 1 bar, that can cause circulation errors. 2. Look around the boiler, radiators and visible pipework for obvious leaks or signs of corrosion. 3. Bleed radiators to remove trapped air: start with the radiator nearest the boiler and work around the house. Catch water with a cloth and a container. 4. After bleeding, re-check the boiler pressure and top up the system if needed (see next steps). 5. Note any unusual noises from the boiler (knocking, gurgling) or a silent pump when the heating is on—these are useful diagnostic clues.

Step-by-step diagnostic and simple fixes:

1. Turn the boiler off and let it cool fully. 2. Check and, if required, top up the system pressure using the filling loop per your boiler manual. Close the filling loop properly when pressure is in the correct range (typically 1.0–1.5 bar cold). Only use the filling loop as described in the manufacturer instructions. 3. Bleed radiators to eliminate airlocks; re-pressurise if pressure drops during the process. 4. Reset the boiler after you have completed the above checks and the system is at correct pressure. On many Baxi boilers hold the reset button for a few seconds (refer to your manual). Wait for the boiler to attempt a normal startup and observe whether E125 returns. 5. With the heating on, listen at the boiler for the pump operating (a steady mechanical hum/vibration). If the pump is noisy, making grinding or screeching sounds, or appears not to run, this suggests pump fault or seizure. 6. If radiators still stay cold at the flow side or you suspect a blockage/sludge, try to identify cold spots on radiators (cold at the bottom or across) which suggest sludge. Repeated circulation failure, persistent low pressure after topping up, or sludge indications usually require a professional flush or component replacement.

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

1. If E125 persists after you have checked and topped up pressure and bled radiators. 2. If system pressure keeps dropping (indicates a leak or PRV fault). 3. If the pump is silent, noisy, or appears seized, or if you suspect electrical faults inside the boiler. 4. If you find a leak you cannot isolate, or if any repair requires removing the boiler casing, accessing gas/electrical connections, powerflushing, replacing the pump, or changing valves/heat exchanger. 5. If the boiler frequently overheats or locks out.

Final notes:

Do not attempt internal repairs to the boiler—pump replacement, PCB, heat exchanger work and gas or mains electrical work must be done by a Gas Safe engineer. Record any actions you take (pressure readings before and after, which radiators bled, whether reset cleared the fault) to give the engineer useful information. If the issue returns or you are unsure at any stage, stop and call a qualified engineer.