Keston E23 Fault Code: Causes, Fixes & Repair Costs
What does the Keston E23 fault code mean?
The E23 fault code on a Keston boiler signals a water filling error. In plain terms, the boiler has detected a problem with the process of maintaining correct system water pressure, and the primary component to investigate is the water pressure sensor. When E23 appears, the boiler enters lockout and stops operating entirely — it will not restart on its own. You must press the Reset button once the underlying issue has been addressed. Simply switching the boiler off and on at the mains will not clear the lockout. E23 sits within Keston's broader fault hierarchy, sitting just below E24 (which flags water pressure loss four or more times within 24 hours), making it an important early warning that pressure management in your system needs attention.
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
- Faulty or failing water pressure sensor Common
The pressure sensor is the component E23 directly implicates. If it has drifted out of calibration, developed an internal fault, or failed outright, it will report incorrect pressure readings to the boiler's control board — triggering a filling error even when the actual system pressure is perfectly normal.
- Genuinely low system pressure Common
Low system pressure is one of the most frequent issues on any sealed heating system. If the water pressure gauge reads below 1 bar, the boiler may correctly identify a filling problem and raise E23. Pressure should sit between 1 and 1.5 bar when the system is cold.
- Water leak causing gradual pressure loss Sometimes
If the system pressure keeps dropping shortly after you top it up, water is escaping somewhere in the circuit — at a radiator valve, a pipe joint, or around the boiler itself. In this situation, simply refilling the system is not a proper fix; the source of the leak must be found and repaired first.
- Loose, corroded, or damaged sensor wiring Sometimes
The electrical connections between the pressure sensor and the control board can work loose over time or suffer corrosion, especially in damp locations. A poor connection can cause intermittent or false signals that the boiler interprets as a filling error.
- PCB misreading the sensor signal Rare
If the printed circuit board itself is faulty, it may incorrectly interpret an otherwise healthy pressure sensor's output and generate a spurious E23 lockout. PCB faults are less common but should be considered when the sensor and wiring have both checked out as sound.
How to fix it
- Check the system pressure gauge DIY safe
Look at the pressure gauge on the boiler — it is usually a dial or a digital reading on the display. A healthy cold-system pressure sits between 1 and 1.5 bar. If the needle or reading is below 1 bar, low pressure is a likely contributor to the E23 code.
- Top up system pressure via the filling loop if needed DIY safe
If pressure is low, use the filling loop (a flexible braided hose or two inline valves, usually located beneath the boiler) to slowly introduce water into the system. Open the valve(s) gradually, watch the gauge, and stop once the pressure reaches roughly 1.2–1.5 bar. Close the filling loop fully before doing anything else. Do not overfill beyond 2 bar.
- Check for visible signs of a water leak DIY safe
Have a look around all accessible radiators, towel rails, and visible pipework for damp patches, drips, or corrosion staining. Check around the boiler casing too. If you find evidence of a leak, do not simply keep refilling the system — a Gas Safe engineer or plumber will need to locate and seal the leak before the E23 can be properly resolved.
- Reset the boiler using the Reset button DIY safe
Once you have addressed pressure and confirmed there are no obvious leaks, press the dedicated Reset button on the boiler's control panel and hold it for the duration specified in your user guide (typically 3–5 seconds). Do not attempt more than two or three resets in quick succession — repeated lockouts without a lasting fix indicate a deeper fault.
- Call a Gas Safe registered engineer if the fault persists Gas Safe engineer
If E23 returns after a reset and pressure has been correctly restored, the water pressure sensor, its wiring, or the PCB will need professional diagnosis. A qualified engineer can test the sensor's output, check continuity in the wiring loom, and assess whether the PCB is producing or amplifying a false fault signal. Keston boilers should be serviced by engineers experienced with the brand. Do not attempt to remove or replace the sensor, wiring, or any internal components yourself.
Parts you may need
- Water pressure sensor · from £22
- Pressure sensor wiring harness · from £18
- Filling loop assembly · from £25
- PCB (printed circuit 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 £90–£280, depending on the underlying cause.
Frequently asked questions
Can I fix Keston E23 myself?
The two homeowner-safe steps are topping up the system pressure via the filling loop (if the gauge reads below 1 bar) and pressing the Reset button. If the code clears and stays away, you may not need an engineer. However, if E23 keeps coming back, the pressure sensor or wiring will need professional testing — this is not a DIY job, and you should contact a Gas Safe registered engineer. If the PCB turns out to be the faulty component, replacement costs can rise to £300–£450 including labour, which is why it is worth getting a proper diagnosis before committing to parts.
How often should I need to top up my boiler pressure?
A well-maintained sealed heating system should hold its pressure for months at a time. Needing to top up more than once every few months suggests water is escaping somewhere. If your Keston boiler is regularly dropping pressure and showing E23, treat it as a sign of a slow leak rather than a quirk of the system, and have an engineer investigate.
Will resetting the boiler damage it if E23 keeps coming back?
An occasional reset is harmless, but repeatedly resetting without fixing the root cause is not a good idea. Most boiler manufacturers — and good practice generally — advise no more than two or three resets before calling an engineer. If E23 is a recurring fault, the boiler is telling you something is consistently wrong, and masking it with resets could allow the underlying issue to worsen.
How much does it typically cost to repair a Keston E23 fault?
For the most common scenario — a pressure sensor replacement carried out by a Gas Safe engineer — expect to pay roughly £90–£180 all in, covering parts and an hour or so of labour. If the wiring harness also needs attention, costs may nudge toward the £200–£280 range. A PCB replacement is considerably more expensive and is only necessary in a minority of E23 cases; if an engineer quotes for a PCB, make sure the sensor and wiring have been properly ruled out first.