Worcester Bosch E2 351 Fault Code: Causes, Fixes & Repair Costs
What does the Worcester Bosch E2 351 fault code mean?
The E2 351 fault code on a Worcester Bosch boiler tells you that the central heating flow NTC (Negative Temperature Coefficient) temperature sensor has become disconnected. The E2 family of codes all relate to a problem with this flow sensor — the component that acts like a thermometer, measuring the temperature of water as it leaves the boiler. The 351 sub-code specifically narrows the fault down to a disconnection, as opposed to a short circuit or outright sensor failure. Without a reliable reading from this sensor, the boiler cannot safely regulate water temperature, so it shuts down and locks out until the issue is resolved. Other E2 sub-codes you may see on Worcester Bosch boilers include those indicating a short circuit in the sensor or complete sensor failure — all point to the same flow NTC circuit but require slightly different remedies.
General guidance only — not a substitute for professional advice. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Loose or dislodged sensor connector Common
The most frequent root cause behind E2 351. The plug connecting the flow NTC sensor to the wiring harness can work loose over time due to vibration or thermal expansion and contraction. A simple re-seating of the connector by an engineer often resolves the fault without any parts being needed.
- Corroded or damaged wiring at the connector Common
Moisture inside the boiler casing, or general age-related deterioration, can cause corrosion at the sensor connector pins or along the wiring harness. This breaks the electrical circuit in the same way as a full disconnection and triggers the 351 sub-code.
- Failed flow NTC sensor Sometimes
The sensor itself can fail over time — the internal resistance element breaks down, giving a reading the boiler interprets as an open circuit (disconnection). This is particularly common on boilers that are several years old or that have experienced repeated overheating events.
- PCB (printed circuit board) fault Rare
If the PCB's input channel for the flow sensor has developed a fault, it may incorrectly report the sensor as disconnected even when the wiring and sensor are perfectly sound. This is a less common but more costly explanation, usually only considered after the sensor and wiring have been checked and found to be healthy.
How to fix it
- Reset the boiler once DIY safe
Press and hold the reset button for approximately three seconds. A single reset can clear a transient glitch that has triggered the code without a genuine fault being present. If the E2 351 code disappears and the boiler runs normally, monitor it over the next day or two. Do not reset more than two or three times — repeated resets mask the underlying problem and delay a proper repair.
- Check that your gas supply is working DIY safe
Verify that other gas appliances in your home — such as a gas hob or gas fire — are working normally. If they are not, the issue may be with your gas supply rather than the boiler. Contact your gas supplier if you suspect a supply problem.
- Check the boiler's system pressure DIY safe
Look at the pressure gauge on your boiler. It should read between 1.0 and 1.5 bar when the heating is cold. If it has dropped below 1 bar, top it up via the filling loop following your boiler's user manual. Low pressure alone is unlikely to cause E2 351, but it is worth ruling out before calling an engineer.
- Call a Gas Safe registered engineer to inspect the sensor wiring Gas Safe engineer
If the fault returns after a reset, you need a qualified engineer. They will open the boiler casing, locate the flow NTC sensor and its connector, and check whether the plug has simply come loose. Re-seating a loose connector is a quick and inexpensive repair. The engineer will also check for corrosion or damage along the wiring harness.
- Have the flow NTC sensor tested and replaced if necessary Gas Safe engineer
The engineer will measure the sensor's electrical resistance and compare it against the expected values at a known water temperature. If the sensor has failed, it will be swapped out for a new one. This is a straightforward parts-and-labour job that typically takes under an hour.
- Have the PCB inspected if the fault persists after sensor replacement Gas Safe engineer
Should the E2 351 code continue even after the wiring and sensor have been confirmed healthy or replaced, the engineer will investigate whether the PCB's sensor input circuit is at fault. PCB repair or replacement is a more involved and costly job, but it is the logical next step if everything else checks out.
Parts you may need
- Flow NTC temperature sensor · from £25
- Sensor wiring harness / loom · from £35
- Sensor connector plug and pins · from £12
- Worcester Bosch PCB (model-specific) · from £180
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £100–£280, depending on the underlying cause.
Frequently asked questions
Can I fix Worcester Bosch E2 351 myself?
The only safe DIY steps are a single boiler reset, checking your gas supply is on, and verifying your system pressure is in the normal 1–1.5 bar range. Any work that involves opening the boiler casing — including reconnecting the sensor plug, testing the NTC sensor, or replacing parts — must be carried out by a Gas Safe registered engineer. Attempting internal boiler work yourself is dangerous and will invalidate your warranty.
What is the difference between E2 351 and other E2 sub-codes on Worcester Bosch boilers?
Worcester Bosch uses the E2 code family to cover all faults related to the central heating flow NTC sensor. The 351 sub-code specifically means the sensor circuit appears open — i.e. disconnected. Other sub-codes within the E2 family can indicate a short circuit in the sensor wiring or a sensor that is giving a reading outside its expected range. While the underlying cause differs slightly, all E2 variants require a Gas Safe engineer to inspect the sensor, its connector, and the wiring harness.
How much does it cost to fix an E2 351 fault on a Worcester Bosch boiler?
Most people pay between £100 and £280 all in, depending on what the engineer finds. If it is simply a loose connector that needs re-seating, you are likely looking at a callout and labour charge only — typically £100–£150. If the flow NTC sensor itself needs replacing, expect to pay £150–£280 including parts and labour. In the less common scenario where the PCB is at fault, costs can rise to £350–£500 or more — but this is rarely the first finding, and a good engineer will exhaust the cheaper possibilities first.
Will the boiler keep shutting down until E2 351 is fixed?
Yes. E2 351 is a locking fault, meaning the boiler shuts itself down and will not restart automatically. Each time you reset it, it may run briefly before locking out again if the underlying fault has not been addressed. Repeated resets do not repair anything — they simply delay diagnosis. If your boiler keeps returning to this code after a reset, book a Gas Safe engineer as soon as possible, particularly in cold weather.