Worcester Bosch E5 fault — your boiler keeps cutting in and out

E5 is a flow-temperature sensor fault. Here's what it means, the couple of things that are safe to check yourself, and why you mustn't keep resetting it.

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What does the Worcester Bosch E5 fault mean?

The Worcester Bosch E5 fault means your boiler's flow-temperature sensor — the part that measures how hot the central-heating water is — has failed or is reading wrong, so the boiler can no longer trust the temperature it's seeing and locks out to stay safe. The most common version, E5 218, is most often shown as flow temperature too high.

In plain terms: that little sensor on the heating flow is the boiler's thermometer. If it's faulty, disconnected, or furred up with limescale, the control board gets a temperature it can't rely on — so it shuts down rather than risk overheating. That's why people search for a Greenstar that "keeps cutting in and out" or "locks out every few minutes".

E5 isn't a nuisance glitch and it isn't a gas emergency — it's the boiler protecting itself. Usually it's the flow-temperature sensor or its wiring. Occasionally the sensor is reading correctly and there's a genuine flow problem behind it (a tired pump, an airlock or sludge stopping the water moving) that's letting the water get too hot.

Codes vary between Greenstar models, so check your boiler manual for the exact wording. You'll usually see E5 with a three-digit cause code after it — E5 218 is most often documented as "flow temperature too high", and E5 332 typically relates to the primary flow exceeding 105°C (some manuals report it as no primary flow). Older Greenstar ranges may not use E5 at all and show EA or E9 instead.

E5 fault — the key facts

Question	Answer
What code is this?	E5 — usually shown with a cause code, most often E5 218 (flow temperature too high) or E5 332 (typically primary flow over 105°C). Codes vary by model, so check your manual.
What does it mean?	The central-heating flow-temperature sensor has failed or is reading wrong, so the boiler locks out rather than trust a temperature it can't rely on.
How serious is it?	Mostly an engineer job. Not a 999 or gas emergency, but don't keep running it — it points to a faulty sensor, its wiring, or a real flow problem.
Can I fix it myself?	Only two safe checks — your system pressure and whether it was recently topped up — plus one reset. The actual repair is Gas Safe work.
Typical repair cost?	Often a sensor swap at around £90–£150, or wiring repair £80–£130. It only gets pricey if the control board (PCB) is involved (industry ranges, not Smart Plan prices).

What causes the E5 fault?

Almost every E5 comes back to the same theme — the boiler can't believe the temperature it's reading on the heating flow. Most of the time that's the sensor or its wiring; now and then the reading is right and there's a real flow problem behind it. Here's what's usually involved, roughly in order of how often it crops up.

A worn or limescaled flow-temperature sensor

The flow sensor is a small NTC thermistor — its resistance changes with temperature, and the boiler reads that to work out how hot the water is. Over the years it can drift, age, or fur up with limescale in hard-water areas, so it starts feeding the board false or sluggish readings. This is the single most common cause of an E5.

Loose, corroded or damaged wiring

The sensor talks to the control board through a thin wire and a plug-in connector. A loose or corroded connector, a chafed cable, or water getting into the connection can break the signal — and the boiler treats a broken signal the same way it treats a dangerous reading: it locks out. A wiring or connection repair is often all it needs.

A real flow problem the sensor is correctly reporting

Sometimes the sensor is doing its job perfectly and the water really is getting too hot. That points to poor circulation — a seized or weak pump, an airlock, low pressure, or sludge and scale in the heat exchanger stopping the heat escaping. When that's the cause, fixing the sensor alone won't clear it.

A faulty control board (least common)

Rarely, the sensor and wiring are fine and the control board (PCB) is misreading the signal it's being sent. It's the least likely cause and the most expensive, so a good engineer rules out the sensor, the wiring and the circulation first.

E5 vs E9 — the difference matters. E5 is the boiler's thermometer lying: the sensor can't be trusted. E9 is the smoke alarm going off: the safety limiter has actually tripped because the water genuinely overheated. Both are lockout faults and both need a Gas Safe engineer if they stick — see our guide to the Worcester Bosch E9 fault if that's the code you're seeing.

E5 causes, symptoms and the likely fix

Cause / code	What you'll notice	Likely fix
Worn or limescaled flow sensor (often E5 218)	Intermittent cut-outs; heating drops out then comes back; display flicking between the code and a temperature.	Test and replace the flow-temperature sensor. Gas Safe engineer.
Loose, corroded or damaged wiring	Comes and goes, sometimes when the boiler's knocked or in damp weather; radiators only partly warming.	Repair or replace the sensor wiring and connector. Gas Safe engineer.
Real over-temperature or flow fault (often E5 332)	Locks out fast after firing; kettling noises; bigger-than-usual gap between flow and return temperatures.	Diagnose the pump, airlock, pressure or sludge behind it. Gas Safe engineer.
Low pressure or recent top-up	Pressure gauge below 1 bar or unusually high after a recent fill; cut-outs since the system was topped up.	Check and correct the pressure to 1.0–1.5 bar — safe to look at yourself.
Faulty control board (rare)	E5 persists after the sensor, wiring and circulation have all been checked and ruled out.	Replace the control board (PCB). The priciest and least common cause.

Is the E5 fault dangerous?

An E5 on its own is not a 999 or gas emergency. The boiler has spotted that it can't trust its temperature reading and shut itself down before anything can go wrong. You don't need to evacuate or call the gas emergency line for an E5.

The National Gas Emergency line, 0800 111 999, is only for a smell of gas or a carbon monoxide alarm going off — not for an E5 code. If you ever do smell gas, that's a different situation: leave the property, call that number, and don't touch any switches.

What you should not do is keep clearing the lockout. After a reset the boiler may fire and run for a few minutes before it spots the fault again and locks out — and if there's a genuine over-temperature behind the E5, forcing it to keep firing in that state can damage the heat exchanger over time. Repeated resets bypass the safety checks that are there to protect it.

The rule is simple: try one reset. If E5 comes straight back, stop and book a Gas Safe registered engineer. Don't sit there hammering the reset button.

How do I fix the E5 fault?

There's a short list of safe checks you can do before anyone comes out. With an E5 it's a shorter list than some codes, because the fix itself is almost always the sensor or its wiring — and that's inside the boiler. None of these checks involve opening the boiler or touching anything to do with gas. If a check feels beyond you, skip straight to booking an engineer.

Safe checks you can do yourself

Work through these in order. They cover the pressure and recent-top-up causes, which are the only parts of an E5 a homeowner can genuinely sort.

1. Check the pressure gauge. When the system is cold it should read about 1.0–1.5 bar. Too low can starve the circulation; oddly high can follow an over-enthusiastic top-up — both are worth noting.

2. Think about whether the system was topped up recently. If E5 started just after someone added water or bled the radiators, an airlock or wrong pressure may be part of it — mention that to your engineer.

3. If the pressure is low, top up using the filling loop — the silver braided hose under the boiler. Open both valves slowly until the gauge reaches 1.0–1.5 bar, then close them fully.

4. Reset the boiler once. Hold the reset button for a few seconds and release. If E5 clears and stays clear, you're done. If it returns, stop — book a Gas Safe registered engineer and don't reset again.

When to call a Gas Safe registered engineer

If E5 comes back after one reset, the cause is inside the boiler or the system — the flow-temperature sensor, its wiring, the pump or circulation, or the control board. None of that is a DIY job. The sensor has to be tested with a meter against its temperature curve and swapped if it's out of spec, and any wiring or board work has to be done by someone qualified. It's illegal and unsafe to attempt gas work yourself.

That's where we come in. Book a one-off repair and we'll come and fix it for you — one of our Gas Safe registered engineers will find the fault and get your heating back on.

How much does it cost to repair an E5 fault?

The good news with E5 is that it's usually one of the cheaper faults to put right, because the most likely culprit is a single small sensor. The figures below are typical UK industry ranges to give you a feel for it. They're not Smart Plan's prices, and they vary by region, model and how easy the boiler is to get at.

A flow-temperature sensor swap — the most common E5 fix — is often around £90–£150. A wiring or connection repair is typically £80–£130, and a diagnostic visit with a reset to confirm the fault usually sits around £60–£90.

It only gets dear if the trail leads to the control board. A replacement PCB part is typically £180–£400, with the full repair often quoted around £300–£500. If the real cause turns out to be circulation rather than the sensor, a replacement pump is usually £130–£400 and a powerflush for sludge around £300–£600.

On an older boiler, the big-ticket repairs are worth weighing against a replacement. As a rough guide, if your boiler is over 10 years old, out of warranty, and needs a PCB, replacing it can make more sense than fixing it. But a straightforward sensor swap on a younger boiler is an easy yes.

Worth knowing: if your boiler's still in guarantee, Worcester Bosch's own customer line is 0330 123 9559. A yearly service — around £110 plus VAT industry-wide — is the best way to catch a tiring sensor or a furring-up heat exchanger before they ever trip an E5, especially in hard-water areas.

Safe checks before you call anyone out

These are the only things worth trying yourself with an E5. Anything beyond them needs a Gas Safe registered engineer.

Check the pressure gauge — it should sit around 1.0 to 1.5 bar when the system is cold.
Note whether the system was topped up or bled recently, and tell your engineer if E5 started just after.
Top up via the filling loop if pressure's low, then close both valves fully.
Reset the boiler once — just once. If E5 returns, stop and book an engineer. Don't keep resetting it.
Don't open the boiler, unplug the sensor, or attempt any gas, wiring or internal work yourself.
If you ever smell gas, that's separate: leave the house, call 0800 111 999, and don't touch any switches.

When a code won't clear — how Smart Plan helps

If you've checked the simple stuff and E5 is still there, the next step is a Gas Safe registered engineer. You've got two easy options.

Smart Plan is a service plan, not insurance. Don't pay for one-size-fits-all — you pick only the cover you want.

Need it fixed now?

Book a one-off repair and we'll come and fix it for you. One of our Gas Safe registered engineers tests the flow sensor and wiring, finds the fault, and gets your heating back on.

Want cover for next time?

Take out an ongoing Smart Plan boiler module and you're sorted when the next code appears. Parts and labour are included up to your cover limit.

Cover is modular, so you only pick what you want — don't pay for what you don't use. Boiler cover runs up to £500 per year if your boiler's under 7 years old, or up to £200 if it's older. A £95 call-out fee applies.

We've looked after over 15,000 customers, we've been trading since 2014, and we're rated on Trustpilot. When a fault code won't budge, we'll come and fix it for you.

Worcester Bosch E5 fault FAQs

Is the E5 fault an emergency?

No — an E5 on its own isn't a 999 or gas emergency. The boiler has locked out because it can't trust its flow-temperature reading, so there's no immediate danger. It does need a Gas Safe registered engineer though, so don't keep running it. The gas emergency line, 0800 111 999, is only for a smell of gas or a CO alarm — not an E5.

What's the difference between E5 and E5 218?

E5 is the family of flow-temperature faults; the three-digit number after it is the specific cause your engineer reads. E5 218 — by far the most common — is most often documented as flow temperature too high. E5 332 typically relates to the primary flow exceeding 105°C (some manuals report it as no primary flow). The exact wording varies between Greenstar models, so check your manual.

Why does my Worcester Bosch boiler keep cutting in and out?

That's the classic E5 pattern. The flow-temperature sensor feeds the boiler a reading it can't trust, so it fires, runs for a few minutes, then locks out again. It usually means the sensor itself is worn or limescaled, or its wiring is loose or corroded — and occasionally a real circulation problem. Check your pressure, then book an engineer if it keeps happening.

Can I keep resetting an E5 fault?

No. Try one reset only. After a reset the boiler may run for a few minutes before it spots the fault again, and if there's a genuine over-temperature behind the E5, forcing it to keep firing can damage the heat exchanger over time. Repeated resets just bypass the boiler's safety checks. If E5 comes straight back, stop and book a Gas Safe registered engineer.

Can I fix an E5 fault myself?

Only the safe basics — checking your pressure, noting if the system was topped up recently, and a single reset. The actual repair is testing and replacing the flow-temperature sensor, repairing wiring, or sorting a circulation fault, all of which is Gas Safe work inside the boiler. Never attempt gas or internal boiler work yourself.

What's the difference between an E5 and an E9 fault?

They're easy to mix up because both are about temperature. E5 means the boiler can't trust its flow-temperature sensor — the thermometer is lying. E9 means the safety limiter has actually tripped because the water genuinely overheated — the smoke alarm has gone off. Both lock the boiler out and both need a Gas Safe engineer if they persist. See our Worcester Bosch E9 fault guide for that one.

How much does it cost to fix a Worcester Bosch E5?

Usually one of the cheaper faults, because it's most often a single sensor. As typical industry ranges, a flow-sensor swap is often £90–£150, a wiring repair £80–£130, and a diagnostic visit £60–£90. It only gets pricey if the control board is involved — a PCB repair is often £300–£500. These are industry guide prices, not Smart Plan's, and they vary by region and model.

Is boiler cover the same as insurance?

No — it's a service plan, not insurance. You pick the cover modules you want, and when something breaks we send a Gas Safe registered engineer to fix it, with parts and labour included up to your cover limit.

E5 still showing? We'll come and fix it for you.

Book a one-off repair or set up an ongoing Smart Plan boiler module. A service plan, not insurance — parts and labour included up to your cover limit.