Baxi E125 fault code: what it means and how to fix it

What does E125 mean on a Baxi boiler?

E125 is Baxi's code for a circulation fault in the primary circuit. The primary circuit is the loop of water the boiler heats and pushes out to your radiators and hot-water cylinder.

The boiler constantly monitors the temperature of this water; if it heats up too quickly or unevenly, the boiler reads that as water not moving properly and locks out on E125 to avoid overheating the heat exchanger.

In plain terms: the burner is making heat, but that heat isn't being carried away around the system at the rate it should be.

The code can appear across several Baxi combi ranges (including Platinum, Duo-Tec and Neta-Tec models) and the broad meaning is the same, though the exact internal sensor logic can differ slightly between ranges.

The important point is that E125 is a protective shutdown — your boiler is doing its job by stopping.

Common causes of E125

The fault is almost always one of the following:

• Low system pressure — the single most common trigger. If pressure drops below roughly 1 bar there isn't enough water in the circuit to circulate properly. This can be caused by a slow leak or by a passing pressure-relief valve.
• Trapped air / airlock — air pockets in the pump or pipework stop water moving freely.
• A seized or failing circulation pump — if the pump won't spin, or runs at the wrong speed, water doesn't circulate.
• Sludge or a blockage — magnetite (black iron-oxide sludge) and limescale can clog the heat exchanger, radiators or pipework and restrict flow.
• A faulty sensor or PCB — less common, but a failed temperature sensor or control board can report a circulation fault that isn't really there.
• A frozen condensate pipe in cold weather can sometimes accompany a lockout, though that usually shows its own symptoms.

What you can safely check

Because E125 is an engineer-only fault, your safe options are limited to the universal homeowner checks. Do not go beyond these:

1. Check the boiler is switched on and the gas supply is on (other appliances like a gas hob will confirm gas is reaching the property).
2. Read the pressure gauge. It should sit between roughly 1 and 1.5 bar when the system is cold. If it's lower, that's likely your cause. See what your boiler pressure should be and boiler pressure too low for the full picture.
3. Top up via the filling loop if pressure is low, bringing it slowly back to 1–1.5 bar, then close the loop fully.
4. Perform one reset following the maker's instructions — see how to reset your boiler. If the boiler locks out again, stop and call an engineer; repeated resets won't fix a real fault and can mask a developing problem.
5. In freezing weather, check the external condensate pipe. A frozen pipe can be thawed gently with warm (not boiling) water — see frozen condensate pipe.

If pressure is correct and the boiler still shows E125, the problem is mechanical (pump, airlock or blockage) and needs professional diagnosis. Bleeding radiators, draining sludge, freeing a pump or replacing parts are all engineer tasks.

When to call a Gas Safe registered engineer

Call an engineer if the pressure is already correct, if E125 returns after a single reset, or if pressure keeps dropping (which suggests a leak). Only a Gas Safe Register engineer may work on the pump, gas valve, flue, sealed combustion circuit, PCB or pressure-relief valve.

A competent engineer will typically:

• Confirm the pressure is holding and look for leaks.
• Test the circulation pump and check it isn't seized or noisy — see noisy central heating pump for related symptoms.
• Check for airlocks and bleed the system.
• Test for sludge or blockages and recommend a chemical flush or power flush if needed.
• Test the flow/return sensors and PCB if the mechanical side checks out.

If you ever smell gas or suspect a leak, call the National Gas Emergency line on 0800 111 999 straight away.

Typical Baxi E125 repair cost

Costs vary by region, boiler age and what's actually wrong. These are indicative 2026 UK ranges:

Job	Indicative 2026 cost
Diagnostic / call-out	£80–£150
Repressurise + bleed system (labour only)	£80–£150
Circulation pump replacement	£250–£450
Flow/return sensor replacement	£120–£250
Chemical flush	£150–£300
Full power flush	£400–£800+
PCB replacement	£300–£600

For more on what drives these figures, see our guide to boiler repair costs.

Related Baxi codes

If your boiler shows a different code, these sibling guides may help: Baxi E119 (low water pressure), Baxi E133 (gas supply / ignition) and Baxi E110 (overheat). You can also browse the full Baxi fault codes hub.

Will boiler cover pay for an E125 repair?

This is general information, not financial advice — always check your own policy wording. Whether an E125 repair is covered depends on your plan.

Most boiler cover plans include parts and labour for breakdowns, so a pump, sensor or PCB failure causing E125 would often be covered — subject to your excess and any exclusions.

However, sludge-related problems are a grey area: many policies exclude system cleaning or power flushing, treating sludge build-up as a maintenance issue rather than a sudden breakdown. Pre-existing faults and older boilers are also commonly excluded.

Before assuming you're covered, check whether your plan includes the central heating system (not just the boiler) and whether flushing is excluded. Our guides on what boiler cover includes and whether boiler cover is worth it explain the trade-offs in detail.

This article is general information, not gas-safety or financial advice. Always have gas appliances checked and repaired by a Gas Safe registered engineer. In a gas emergency, call the National Gas Emergency line on 0800 111 999. Costs are indicative UK guides for 2026.