Water pressure sensor is open circuit/disconnected
The E28 error code on Keston boilers indicates water pressure sensor is open circuit/disconnected.
Keston E28 means: water pressure sensor is open circuit/disconnected. The usual causes are leak in the heating system (radiators, pipes, or valves), faulty pressure relief valve (prv) releasing water or failed expansion vessel or loss of pre-charge. You can safely reset the boiler once — if E28 returns, do not keep resetting. A qualified heating engineer should diagnose the root cause.
What Does E28 Mean
The E28 code is shown by the boiler’s control board when it detects water pressure sensor is open circuit/disconnected. The boiler then stops instead of continuing to run in that condition: the code is the appliance reporting a problem, not proof that the boiler is broken.
| What you see on the boiler |
|---|
| The display shows E28 and the boiler stops until the fault is cleared |
Common Causes
Causes documented in 2 technical sources.
| Cause |
|---|
| Leak in the heating system (radiators, pipes, or valves) |
| faulty pressure relief valve (PRV) releasing water |
| failed expansion vessel or loss of pre-charge |
| recently bled radiators without topping up |
| faulty pressure sensor giving incorrect reading |
| automatic air vent leaking |
Safety Warning
E28 involves electrical or pressure-related components. Do not attempt repairs without proper qualifications. Ensure the boiler is electrically isolated before any inspection. If you notice water leaks, unusual sounds, or pressure anomalies, contact a qualified heating engineer immediately.
Parts & Prices
Prices shown are indicative. Actual prices and availability vary by region.
Step-by-Step Diagnosis
Check the boiler pressure gauge — normal operating pressure is 1.0-1.5 bar (15–22 psi) when cold
Inspect all visible pipework, radiators, and valves for signs of leakage
Check the pressure relief valve discharge pipe — if water is dripping, the PRV may be faulty or the expansion vessel has failed
Test the expansion vessel — with the system cold and drained, check the Schrader valve on the vessel
air should escape at the correct pre-charge pressure (typically 0.75-1.0 bar, 11–15 psi)
Inspect the pressure sensor connections
Check automatic air vents for signs of weeping
How to Fix It
Replace the faulty thermistor/NTC sensor
repair or replace damaged wiring
clean corroded connectors
if the PCB input is damaged, replace the PCB
Refer to the Keston service documentation for the detailed procedure. Only a qualified engineer should carry out these repairs.
Diagnostic Tools
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Affected Models
Keston models that can display fault code E28:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Keston models | — | Possible |
Frequently Asked Questions
Replace the faulty thermistor/NTC sensor. According to the technical documentation, this is the first check on the list for E28.
E28 is not classified as a high-severity fault, so the boiler can be reset once. If E28 comes back, stop resetting: the underlying cause is still there and needs a qualified heating engineer.