Error D.44

Safety first

1) If you smell gas, evacuate the property immediately, do not operate electrical switches, and call the gas emergency number for your area.

2) If the boiler is hot and showing overheating symptoms, switch it off at the isolating switch and allow to cool. Do not attempt internal repairs.

3) If the boiler has locked out repeatedly, avoid repeated resets — this can conceal a persistent safety issue.

Initial homeowner checks (safe, non-invasive)

1) Note the exact error code (D.44) and any other codes in the fault history or display. Take a photo for the engineer.

2) Try a single controlled reset: press and hold the boiler reset button for a few seconds. Wait for a normal ignition attempt. If it clears and stays OK for a sustained period, monitor for recurrence.

3) Check mains power to the boiler and the room thermostat/settings so the fault is not caused by no demand or incorrect controls.

4) Check the system water pressure on the boiler gauge; correct pressure is usually around 1–1.5 bar (consult your boiler handbook). If pressure is very low, follow the handbook to top up via the filling loop, but only if you are comfortable doing so. If unsure, do not attempt.

5) Look for obvious signs: water leaks, wet wiring, corrosion, blocking of the external flue, or frozen/blocked condensate pipe. Remove any visible external obstructions from the flue outlet.

6) Listen for the pump running during a heat call. If the pump is silent and the boiler attempts to fire, note this — a failed or blocked pump can create temperature or flow errors.

Diagnostic steps you can safely perform and record (do not open the boiler or touch internal components)

1) Record when the fault occurs: on CH demand, DHW demand, after a cold start, after a reset, or continuously. Note any pattern and exact sequence of events.

2) Check fault history via the boiler display (last 10 faults) and note any associated codes (e.g., F.29, F.71, F.87, etc.). This helps the engineer pinpoint whether the issue is flame detection, sensors, pump, gas valve or PCB related.

3) Bleed radiators to remove trapped air if you suspect large temperature differentials between flow and return. After bleeding, re-check system pressure and top up if required.

4) If you see water inside the external condensate trap or evidence of damp around the control box, note it — moisture on electronics can cause ionisation/flame detection faults.

What to avoid (important)

1) Do not access internal boiler components, adjust the gas valve, attempt to clean or reposition electrodes, or work on the PCB unless you are a qualified Gas Safe engineer. These are live and gas-bearing parts and are dangerous.

2) Do not repeatedly reset the boiler to clear the code without investigating — a persistent safety fault needs professional diagnosis.

Information to give your engineer when you call

1) Exact error: D.44 (digitised ionisation / potential error) and any other fault codes from the history.

2) What you did: single reset? pressure top-up? any recent servicing or parts changed? Any smells, leaks, or unusual noises?

3) System observations: boiler locks out on CH or DHW, pump sounds, pressure readings, visible condensation or water ingress, pattern of when fault appears.

When to call a professional

1) If the fault persists after a single reset, if it recurs, or if there are other associated fault codes, stop attempts to run the boiler and call a Gas Safe registered engineer. This fault commonly needs specialist testing of the ionisation/flame detection circuit, ignition electrode and lead, gas valve operation, flow and return NTCs, pump function, wiring harness and the main PCB.

2) If you find water on or near the electronics, or if you cannot bring system pressure to correct levels, call an engineer.

Summary of likely professional checks and tests (for your information only)

1) Engineer will read fault history and carry out live diagnostics: measure flame signal, check electrode/ignition lead, inspect/clean or replace electrode, test gas valve coil resistance, check pump and flow sensor, test flow and return NTC resistances and connections, test pressure and water flow sensors, and inspect PCB and eBUS communications.

2) The engineer may also check for black discharge or shorting on ignition cables, check earthing/grounding, and inspect the flue gas temperature sensor or flue route if flue temps are implicated.

Final note

D.44 should be treated as a safety-related lockout. Carry out only the safe visual checks and one controlled reset. If the fault returns, or if you are unsure about any step, switch the boiler off and contact a Gas Safe registered engineer, providing them with the D.44 code, any additional fault codes, and the observations you recorded.