Baxi E110 Fault Code: Overheat Explained

What does E110 mean on a Baxi boiler?

The E110 fault code on a Baxi combi or system boiler means the appliance has detected an overheat — the flow temperature has climbed too high, so the boiler has shut itself down to protect the system. In plain terms, the boiler thinks the water leaving it is dangerously hot and has locked out as a safety measure.

This is the boiler doing its job. An overheat lockout is a built-in safety feature, not a sign that anything has gone catastrophically wrong. The question is why it overheated — and in most cases the answer is that hot water isn't moving around the system the way it should. When heat can't escape from the boiler into your radiators fast enough, the temperature inside the heat exchanger spikes and the overheat sensor trips.

Common causes of a Baxi E110 overheat

Most E110 faults trace back to poor circulation or a sensor problem. Typical causes include:

• Low water pressure — if there isn't enough water in the sealed system, what's left heats up too quickly and the boiler overheats.
• Trapped air — air pockets in the radiators or pipework stop water circulating properly, so heat builds up in the boiler instead of dispersing.
• Sludge or poor circulation — a build-up of black sludge and debris restricts flow through the radiators and heat exchanger, causing hot spots and overheating.
• A stuck or failing circulation pump — if the pump isn't pushing water round the system, heat has nowhere to go.
• A faulty flow or overheat thermistor (sensor) — the temperature sensor itself can fail and report a false overheat, locking the boiler out even when it isn't actually too hot.

The first two or three of these you can investigate safely at home. The pump, sensors and a system flush are engineer territory.

The safe checks you can do yourself

None of the steps below involve removing the boiler casing or touching any gas part. They're the homeowner-safe checks that often clear an E110 caused by low pressure or trapped air.

1. Check the pressure gauge

Find the pressure gauge on the front of the boiler (some models show it on a digital display). When the system is cold, healthy pressure is around 1 to 1.5 bar, rising towards roughly 2 bar as the heating warms up. If the needle sits below about 1 bar, low pressure could well be behind the overheat. Our guide to low boiler pressure walks through this in more detail.

2. Top up the pressure via the filling loop

Topping up through the filling loop — usually a silver braided hose with one or two valves underneath or near the boiler — is a safe homeowner job. With the boiler switched off:

1. Open the valve(s) slowly until you hear water flowing in.
2. Watch the gauge and close the valve(s) once it reaches about 1.2–1.5 bar. Don't overshoot — too much pressure can trip the safety valve.
3. Check both valves are fully closed, then switch the boiler back on.

3. Bleed your radiators

If a radiator is cold at the top while warm at the bottom, there's trapped air stopping water circulating — a classic overheat cause. Bleeding the radiators with a radiator key releases that air. Afterwards, re-check the pressure on the gauge, as bleeding usually drops it slightly and you may need to top up again.

4. Reset the boiler — once

Once the pressure is right and any air is out, press and hold the reset button on the front panel for a few seconds and give the boiler a minute to fire. A single reset to clear the overheat lockout is fine. Repeatedly resetting a boiler that keeps overheating is not — if E110 returns, stop and book an engineer rather than cycling it again.

When the E110 keeps coming back

If the pressure was fine, or you topped up and bled the system and E110 returns, the cause is usually something an engineer needs to diagnose. The likely culprits are a stuck or failing pump, a faulty flow or overheat thermistor, or sludge restricting circulation that needs a power flush. All of these sit within the sealed circuit or behind the casing, so they're engineer-only.

If you have boiler cover in place, a persistent overheat is exactly the kind of breakdown it's meant for — you call the provider and they send an approved engineer rather than you paying a one-off bill. This is closely related to the Baxi E1 fault code, which also points to a water-side or circulation problem; if you've seen both codes, it's worth mentioning that to your engineer.

Indicative repair costs

If you don't have cover and need to pay for the repair yourself, the figures below are indicative ranges for 2026 to help you budget. Actual prices vary by region, the engineer and the fault — always get a quote first.

One unexpected pump or flush bill can cost more than a year of cover, which is why many people weigh up a monthly plan instead. Our guides on the best boiler cover and cheap boiler cover explain how to compare what you actually get for the price.