Warmflow E46 Fault Code: Causes, Fixes & Repair Costs
What does the Warmflow E46 fault code mean?
The E46 code appears on Warmflow boilers — including the Agentis series — when the control board detects a problem with the system pressure sensor. This could mean the sensor has lost its electrical connection, is producing readings outside the expected range, or has failed outright. As a safety measure, the boiler locks out rather than continuing to operate without reliable pressure data. The fault typically displays in red on the boiler's screen to indicate a lockout condition rather than a simple warning.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. 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
- Disconnected or loose sensor wiring Common
The wiring harness or connector leading to the pressure sensor has come loose or detached. This is the single most common cause of E46. Vibration over time can gradually work a connector free, and it is often the quickest fault to resolve — reconnecting the plug restores normal communication with the control board.
- Failed pressure sensor Common
The pressure sensor itself has developed an internal fault and is either returning readings that fall outside the acceptable range or has stopped responding altogether. The Warmflow Agentis range uses a specific CHBL water pressure sensor matched to the 21–33 kW models, so fitting an incorrect part can also produce this code.
- Wiring damage or corrosion Sometimes
In older boilers, the wiring between the sensor and the PCB can suffer from corrosion at the connector pins, chafing, or heat damage. Even partial damage can cause intermittent or invalid signals that the control board interprets as a sensor fault.
- PCB communication fault Rare
If the sensor and its wiring test as healthy, the issue may lie with the PCB itself — specifically, the input circuit that reads the sensor signal. A failing PCB may incorrectly flag a sensor error even when the sensor is working correctly. This is a less common cause but should be investigated if sensor replacement does not clear the fault.
How to fix it
- Reset the boiler once or twice DIY safe
Press and hold the reset button as described in your boiler's user guide. A transient glitch can occasionally trigger the E46 code, and a single reset may clear it. If the lockout returns immediately or after only a short period of normal operation, a reset alone will not fix the underlying problem — avoid repeatedly resetting as this can mask a genuine fault.
- Check the boiler display and note any additional information DIY safe
Take a clear photo of the display showing the E46 code. Note whether any other codes or symbols appear alongside it. This information is useful when speaking to an engineer and helps them arrive prepared with the right parts.
- Verify there are no other obvious system issues DIY safe
Check that the system pressure gauge (if visible) reads within the normal operating range — typically 1 to 1.5 bar when cold. If pressure is very low, top up via the filling loop according to your user manual. However, be aware that with a pressure sensor error active, the boiler may not be able to confirm pressure accurately until the sensor fault is resolved.
- Have a qualified OFTEC-registered engineer inspect the sensor wiring Gas Safe engineer
Because Warmflow produces oil-fired boilers, work on the boiler's internal components must be carried out by an OFTEC-registered engineer (not solely a Gas Safe engineer). The engineer will check whether the pressure sensor connector is fully seated and undamaged — this is the most common fix and can be resolved quickly if a loose plug is the only issue.
- Engineer to test and replace the pressure sensor if required Gas Safe engineer
If the wiring is intact but the sensor is producing invalid readings or none at all, the engineer will replace the pressure sensor. Warmflow Agentis models require the correct CHBL sensor for the specific kilowatt rating — fitting the right part is important for the fault to clear reliably.
- Engineer to inspect the PCB if the fault persists after sensor replacement Gas Safe engineer
Should the E46 code return after a new sensor has been fitted and wiring confirmed as sound, the PCB's sensor-reading circuit will need to be examined. The engineer will also carry out a broader inspection of the heat exchanger, pump, and other components before recommending a PCB replacement, as this is a more significant repair.
- Contact an OFTEC-registered engineer if you have not already done so DIY safe
If the boiler remains in lockout after one or two resets, arrange a visit from an OFTEC-registered engineer. You can find registered engineers at the OFTEC website (oftec.org). Attempting to open up the boiler or disconnect components yourself is not recommended and could invalidate your warranty — Warmflow requires annual servicing by a qualified engineer to keep the warranty valid.
Parts you may need
- Warmflow CHBL Water Pressure Sensor (Agentis 21–33kW) · from £25
- Pressure sensor wiring harness / connector · from £15
- Warmflow Agentis PCB (control board) · from £220
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–£250, depending on the underlying cause.
Frequently asked questions
Do I need a Gas Safe engineer or an OFTEC engineer to fix an E46 on my Warmflow boiler?
Warmflow boilers are oil-fired, so you need an OFTEC-registered engineer rather than (or in addition to) a Gas Safe engineer. OFTEC registration is the oil-heating equivalent of Gas Safe and ensures the engineer is qualified to work safely on oil appliances. You can search for registered engineers at oftec.org. Using an unqualified person will also invalidate your Warmflow warranty.
How much should I expect to pay to fix a Warmflow E46 fault?
If the fault turns out to be a loose connector or a failed sensor — which covers the majority of E46 cases — the total bill including call-out, labour, and parts will typically fall between £100 and £250. If the PCB needs replacing, costs rise considerably, often into the £300–£500 range when you include labour, so it is worth getting a quote before authorising that work.
Can I reset my Warmflow boiler myself to clear the E46 code?
Yes, you can try pressing the reset button once or twice. Occasionally a transient electrical glitch causes the code to appear, and a reset clears it permanently. However, if the E46 returns after resetting — or comes back within a short time — there is an underlying fault with the sensor or its wiring that only an OFTEC engineer can properly diagnose and repair. Repeated resetting is not advisable.
Will my Warmflow warranty cover an E46 sensor fault?
Warmflow offers a 24-month warranty on parts and workmanship from the date of manufacture, and 5 years on the water jacket and thermal store on combi models. A pressure sensor replacement may be covered if the boiler is within warranty and has been serviced annually by a qualified engineer — Warmflow requires this to keep the warranty valid. Check your warranty documentation and contact Warmflow or your installer before arranging independent repairs if you think you may be within the warranty period.