Error E30

Safety precautions:

- Before doing anything isolate the boiler electrical supply at the mains isolator or fusebox. If you are going to remove the case or touch internal components also shut off the boiler gas isolation valve and the system water feed if appropriate. Wait a few minutes for capacitors to discharge.

- Never operate the boiler with the casing removed. If you are not confident working safely with mains electricity, do not proceed and call a Gas Safe engineer.

Initial homeowner checks you can safely do:

1) Note the fault and try a single reset using the boiler reset button. If the fault clears and does not return, monitor the boiler — intermittent faults often come back and will still need an engineer.

2) With the boiler powered down at the isolator, remove the outer case following the manual instructions (keep screws and note how the panel fits).

3) Locate the flow sensor (thermistor) on the flow pipe or its wiring loom. On many Keston combis it is a small clip-on sensor or a probe with a 2- or 3-pin connector labelled FLOW.

4) Visually inspect the sensor, connector and wiring for signs of water, corrosion, bent pins, broken insulation, rodent damage or loose/poorly seated connectors.

Specific diagnostic checks (only if competent and with mains OFF):

5) Unplug the sensor connector from the wiring loom/PCB and inspect the pins for corrosion or debris. Re-seat the connector firmly if it was loose and check whether the connector clip locks.

6) If you have a digital multimeter and are competent to use it with the appliance isolated, measure the resistance between the sensor wires (across the two thermistor leads). A working thermistor will show a finite resistance (it varies with temperature) — it should NOT read near 0 ohms. If you read very low resistance (near zero) that indicates a short. Also measure from each sensor lead to boiler chassis earth; you should read open circuit (no continuity). A continuity to earth indicates a short to chassis.

7) If the wiring or connector shows a short or obvious damage, trace the wiring back as far as you can and look for crushed or chafed sections. Sometimes a short is local to the connector and can be cured by cleaning or replacing the connector. Do not tape over a fault if you are unsure — call an engineer.

If you find a faulty sensor or wiring:

8) Replace the flow thermistor/sensor with the correct Keston part. Sourcing and replacing the sensor is a job best done by a Gas Safe engineer if it requires draining or disturbing water or gas connections. If the sensor is clip-on and accessible you may be able to replace it after isolating power and gas, but only proceed if you are experienced and confident.

9) After replacement, reassemble, restore water/pressure if you drained any, restore gas and electrical supplies, and reset the boiler. Confirm normal operation and check for reoccurrence of the fault.

If the sensor and wiring test OK but E30 persists:

10) The control PCB or internal electronics may be faulting or giving an incorrect short reading. At this point a qualified engineer should inspect the control board and perform further electrical diagnostics.

Final notes and when to call a professional:

- Any work beyond visual inspection and simple connector reseating (electrical testing, sensor replacement, any work that disturbs gas or sealed water circuits) should be carried out by a Gas Safe registered engineer. Working on gas appliances and internal high-voltage components without the correct qualification is dangerous and may be illegal.

- If the fault keeps recurring after a reset, or if you find water in connectors, damaged wiring, or are uncertain about any step, switch the boiler off and call a qualified engineer. Take photos of connectors, wiring and the error code to help the engineer diagnose the issue more quickly.