Main E125 fault code: circulation fault explained

What does the Main E125 fault code mean?

The Main E125 fault code means a water circulation fault in the boiler's primary circuit: water is not moving through the boiler the way it should while the burner is lit. The usual reasons are a pump that has jammed, failed or lost its power supply, air trapped in the circuit, sludge or scale narrowing the heat exchanger and pipework, or closed valves and very low pressure starving the flow. You can check the pressure gauge, the valves and the controls yourself, and reset once. The rest sits behind the casing and needs a Gas Safe registered engineer.

Main is part of the Baxi group, so Eco Compact and Eco Elite boilers show their fault codes as E-numbers and use the same E-code system you will see on Baxi and Potterton. The code numbers and their meanings are shared across all three ranges. The exact wording on your display can vary by model year, so check your own Main user guide for the text it shows alongside the number.

Main does not publish a homeowner page for this code. Its fault-code help runs through Baxi, which owns the brand, and Baxi's homeowner error-code help covers E23, E53, E133, E119 and E128. E125 is not one of them, so the code appears mainly in installer-facing material. That is why searching the maker's own site for E125 comes back with very little, even though the code is genuine.

Key facts

The quick version, before the detail.

• Meaning: a water circulation fault in the primary circuit, so water is not moving through the boiler properly while the burner is lit.
• Main shares the Baxi group E-code system, so E125 means the same thing on Main, Baxi and Potterton boilers.
• Not a pressure code: low pressure has its own code on Main boilers, E119, which means the gauge has dropped below 0.5 bar.
• DIY-fixable? Only the pressure, valve and control checks below, plus a single reset using the method in your Main user guide. If E125 returns, book an engineer.
• If E110 is showing as well, reset once at most and stop there, because repeated resets can mask a genuine overheat fault.
• Smart Plan boiler and central heating cover funds covered repairs, parts and labour, up to £500 per 12-month period if your boiler is under 7 years old, or up to £200 if it is over 7. Work caused by sludge, scale or corrosion is excluded, and a failed heat exchanger or circuit board is treated as beyond economic repair rather than repaired.

Why does E125 appear on a Main boiler?

E125 is a symptom rather than a diagnosis. It tells you the water is not moving, not why. On a Main boiler the usual causes are a pump that has jammed, failed or lost its supply, air trapped in the boiler or the system, sludge or scale narrowing the heat exchanger and pipework, and closed valves or a blockage that stops part of the system circulating at all.

Low pressure is worth checking, but it is not what E125 means. Main gives low pressure its own code, E119, which means the pressure has fallen below 0.5 bar. Very low pressure can still starve circulation, so read the gauge first, but E125 itself is about flow. E110, the overheat lockout, comes from the same root causes on Main boilers, a jammed pump or air in the circuit, so it is not unusual to see the two together. If E110 is showing, reset once at most, then book a Gas Safe registered engineer.

E125 causes and what happens next

What you can safely check yourself

Four checks are safe without opening the boiler. Work through them in order and stop after step 4, because anything further means removing the casing or touching live electrics.

1. Read the pressure gauge. On a Main boiler the normal cold range is roughly 1.0 to 1.5 bar, and the boiler stops rather than run dry once pressure falls below 0.5 bar.

2. If pressure is low, repressurise once with the boiler switched off and cool. On an Eco Compact or Eco Elite the filling loop is the silver braided hose beneath the boiler with a valve at each end. Open both valves slowly, close them at roughly 1.0 to 1.5 bar, then disconnect a temporary loop. If the pressure keeps falling you probably have a leak or a tired expansion vessel, so do not keep topping it up.

3. Check the controls and valves. Radiator and isolation valves should be open, the thermostat or programmer should be calling for heat, the boiler should be powered and the gas on, and there should be no visible leaks.

4. Reset once, using the method set out in your Main user guide. Reset once only, and stop there if E110 is showing as well, because repeated resets can mask a genuine overheat fault. Book a Gas Safe registered engineer instead of pressing it again.

Stop there. If E125 comes straight back, the fault needs investigating properly. Repeated resetting will not cure a jammed pump, air in the circuit or a blocked heat exchanger, and it leaves the boiler firing against water that is barely moving.

When to call a Gas Safe registered engineer

Call a Gas Safe registered engineer if E125 returns after one reset, if E110 is showing alongside it, or if the pressure keeps falling however often you top it up. Everything left is engineer work: removing the casing, venting and purging the boiler, electrical readings at the circuit board and pump, freeing or replacing the pump, and cleaning or replacing a blocked heat exchanger.

If E125 is on your display today, the route is a one-off repair. You can book one with us, or call us on 0333 772 6247, and we will arrange a Gas Safe registered engineer to look at the circulation fault. For E125, ask for Call-out and diagnosis rather than a Fixed Price Repair, because a Fixed Price Repair excludes works on the boiler's circuit board (one-off works T&Cs p.7 §1(b)(i)), and a circulation fault often needs diagnosis before anyone can price the work. One-off appointments run Monday to Friday, 09:00 to 17:00, and not on bank holidays. A one-off repair is paid up front, it carries no workmanship guarantee, a job may take more than one visit, and someone has to be at the property, because a no-access visit is cancelled and the payment is not refunded.

A Smart Plan boiler and central heating module is a separate thing, and it is for future breakdowns rather than the code your boiler is showing today, which counts as a pre-existing fault. It funds covered repairs, parts and labour, up to £500 per 12-month period if your boiler is under 7 years old, or up to £200 if it is over 7, and you pay anything above that limit yourself. Which limit applies depends on your boiler's age at the time of the repair, so check the age on the boiler or its paperwork. We work with a national network of thousands of Gas Safe registered engineers, and cover-plan call-outs run Monday to Friday, 08:00 to 18:00, and within those hours we aim to get an engineer out to you within two working days. That is a target, not a promise.

Not every E125 cause is a covered repair, and that matters a lot on this fault. The cover terms exclude work caused by sludge, scale deposits, rust or corrosion, they exclude adjusting settings and resetting equipment, and they exclude repressurising (cover plan T&Cs general exclusions 1, 2 and 22). The boiler module also excludes works relating to electrical, water supply or booster pumps (boiler exclusion 2(d)), so ask us which side of that line your pump falls before you assume it is funded. If the heat exchanger or the circuit board has failed, the terms treat the boiler as beyond economic repair, so you receive a contribution payment set at the lower of the equipment's retail value or your cover limit less any work already completed, rather than a repair (cover plan T&Cs p.8 §2.1(c) and p.23 §9.5). Read those terms before you assume an E125 repair would be funded.

A £95 call-out fee, paid in advance, applies in your first 30 days, for faults the plan does not cover, if the engineer cannot get access, and for early annual-service requests. Cover still applies during those first 30 days, but you pay the £95 in advance and you pay for any works in advance too (cover plan T&Cs p.23 §9.1). Using a module starts a 12-month agreement period from the first time you use a service. There is a 14-day cooling-off period, but it ends the moment a service is carried out, and leaving early after that costs the remaining months or 75% of the outstanding balance. Smart Plan is a service plan, not insurance. It arranges and funds covered repairs up to the limits on your plan rather than paying out a cash sum, and it is from UK Boiler Company Ltd, trading since 2014 (company number 09078640).

One safety note. E125 is a circulation fault rather than a gas fault, but if you smell gas or suspect carbon monoxide, do not wait for an engineer. Call the National Gas Emergency Service on 0800 111 999 straight away, open the windows, turn the gas off at the meter if you can safely reach it, do not touch any electrical switches, and leave the property.

Main E125 fault code FAQs

Seeing E125 on your Main boiler?

Book a one-off repair and we will arrange a Gas Safe registered engineer to look at the circulation fault. For E125, ask for Call-out and diagnosis rather than a Fixed Price Repair, because a Fixed Price Repair excludes works on the boiler's circuit board (one-off works T&Cs p.7 §1(b)(i)). One-off appointments run Monday to Friday, 09:00 to 17:00, they carry no workmanship guarantee, and a job may take more than one visit. A Smart Plan boiler and central heating module is for future breakdowns rather than the code showing today: it funds covered repairs up to £500 per 12-month period if your boiler is under 7 years old, or up to £200 if it is over 7, though work caused by sludge, scale or corrosion is excluded, and a failed heat exchanger or circuit board is treated as beyond economic repair, which pays a contribution towards a replacement instead (cover plan T&Cs p.8 §2.1(c) and p.23 §9.5). It is a service plan, not insurance. A £95 call-out fee, paid in advance, applies in your first 30 days, for faults the plan does not cover, no-access visits and early annual-service requests, and in those first 30 days any works are payable in advance too. Cover-plan call-outs run Monday to Friday, 08:00 to 18:00, and within those hours we aim to get an engineer out to you within two working days. Using a module starts a 12-month agreement period once you first use a service; leaving early costs the remaining months or 75% of the outstanding balance.

Helpful links

• All Main boiler fault codes
• Baxi boiler fault codes (the same E-code system)
• Baxi E110 fault code (overheat lockout)
• Baxi E119 fault code (low water pressure)
• Boiler losing pressure
• No heating? Book a repair
• Boiler repair
• Boiler & central heating cover
• Baxi professional error-code list
• Baxi homeowner error-code help (E23, E53, E133, E119, E128)
• Check an engineer on the Gas Safe Register