Overview
The E125 fault on a Baxi Platinum indicates a primary circuit circulation fault — in plain terms the boiler has detected that heated water is not circulating correctly through the central heating circuit (flow/return, radiators, heat exchanger). The boiler will usually lock out or reduce operation when it cannot circulate water safely, to protect the heat exchanger and other components. This error most commonly occurs because of low system pressure, air trapped in the system (airlocks), a blocked/partially blocked circuit (sludge, limescale or debris), or a failing circulation pump. Less common causes include a leaking pressure relief or automatic air vent, or electrical/PCB faults that affect pump control. Severity ranges from a minor inconvenience (cold radiators) to a potentially damaging situation if the boiler repeatedly overheats or is run with poor flow — so it should be investigated promptly. Many basic checks are safe for a homeowner: checking the pressure gauge, bleeding radiators and looking for obvious leaks. Anything that requires removing the boiler casing, working on gas or electrical components, replacing the pump, carrying out a powerflush or fixing leaks on the primary circuit should be done by a Gas Safe registered engineer. If in doubt, stop and call a professional.
Possible Cause: Primary circuit error circulation fault
Troubleshooting Steps
Safety first
- If you attempt any checks, switch the boiler off at the mains and allow it to cool before touching pipework or radiators. Do not remove the boiler casing or tamper with gas/electrical components — those tasks must be done by a Gas Safe engineer.
- If you find a significant leak, turn off the water feed and the boiler electrical supply and call a Gas Safe engineer immediately.
Initial homeowner checks
1. Note the displayed code (E125) and any flashing lights. Record the boiler pressure reading from the pressure gauge.
2. Visually inspect around the boiler, radiators and visible pipework for signs of leaks or corrosion. Look for dripping, damp patches or pooling water.
3. Listen to the boiler when it tries to run: is the pump making a humming, rattling or dead-silent noise? Unusual noises can indicate a failing or seized pump.
4. Check radiator temperatures: start the heating and feel radiators near the boiler and at the far end. If radiators near the boiler are hot but others remain cold, that suggests a circulation problem downstream.
Basic DIY fixes you can try
1. Bleed radiators to remove trapped air: with the heating off and system cooled, use a radiator key to open the bleed valve until air hisses out, then close when water appears. Work from the radiator nearest the boiler outwards. Re-check system pressure afterwards.
2. Check and top up system pressure if low: many Baxi boilers should sit around 1.0–1.5 bar when cold (consult your manual for the exact recommended range). If pressure is low and you are confident doing this, follow the boiler manual to use the filling loop: reopen the filling loop valves slowly while watching the gauge, stop at the recommended pressure, then secure the loop per the manual. If you are unsure how to do this, call an engineer. Do not over-pressurise.
3. Reset the boiler after the above steps: follow the manufacturer instructions (usually a reset button or switch) or switch the boiler off and on again. Observe whether the E125 clears and whether radiators begin to warm evenly.
Further diagnostics and when to stop
1. If the pressure drops again shortly after topping up, or you find a leak, turn the boiler off and call a Gas Safe engineer — the system is losing water and needs fault-finding and repair.
2. If radiators remain cold after bleeding and repressurising, and you hear little or no pump noise, the pump may be blocked, seized or electrically faulty. Do not attempt to dismantle the pump; call a Gas Safe engineer to inspect, test and, if necessary, replace the pump.
3. If you suspect blockages from sludge or limescale (radiators unevenly hot, dark residue when bleeding), a professional powerflush or chemical clean is usually required.
4. If the boiler still shows E125 after basic checks and reset, or if there are electrical symptoms (fuse/trip issues, PCB-related errors), stop and contact a Gas Safe registered heating engineer.
Information to give the engineer
- Boiler make and model (Baxi Platinum) and the exact error code E125
- Current boiler pressure reading and whether it falls after topping up
- Any visible leaks, noises from the pump, or recent work on the system
- What steps you have already taken (bled radiators, topped up pressure, reset boiler)
Final note
E125 is a circulation fault that can sometimes be cleared by simple homeowner checks (bleeding radiators, repressurising, reset). However, persistent faults, pump issues, leaks, blockages or any work requiring access inside the boiler must be done by a Gas Safe registered engineer to ensure safety and to protect the appliance.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi Platinum.