Error D.44

Safety first

1) If you smell gas: evacuate the building, do not operate electrical switches, turn off the gas supply at the meter if it is safe to do so, ventilate, and call your gas emergency number and a Gas Safe engineer immediately. Do not attempt internal repairs.

2) If you do not smell gas, isolate electrical power to the boiler only if instructed by an engineer; do not open panels or attempt internal live testing unless you are qualified.

Initial homeowner checks (safe, simple checks you can do)

1) Note the exact error code (D.44) and any other F codes or messages on the display. Write down any recent events (power cut, gas work, freezing temperatures, condensate drain problems).

2) Try a simple reset: switch the boiler off at the front panel or isolator, wait 1 minute, switch back on. If it clears and the boiler runs normally for an extended period, monitor closely; intermittent faults still need a service engineer.

3) Check the gas supply: confirm other gas appliances work (hob/oven). Check the gas meter/isolator is on. If the gas supply is interrupted or low, mention this to the engineer.

4) Inspect the flue termination and air inlet externally: ensure nothing is blocking the flue or air intake (birds’ nests, leaves, snow, debris). A blocked flue can affect combustion and flame detection.

5) Check condensate drain and condensate trap (external and visible routes) for freezing or blockages if temperatures are low. Excess condensate in the combustion area can damp electrodes and cause faulty ionisation readings.

6) Check central heating water pressure and visible leaks; while not a primary cause of D.44, severely abnormal system conditions can produce other faults in parallel.

Information to collect for the engineer

1) Boiler model and serial number (from rating plate). 2) Exact code history (D.44 plus any F codes), when the fault started, and any actions you have taken (reset, checks performed). 3) Observed behaviour (clicking ignition, number of ignition attempts, whether boiler attempts to light and then locks out).

What a qualified engineer will check and do (technical diagnostic and repair steps)

1) Enter service/diagnostic menu to read live flame/ionisation signal values and ignition sequence logs. Compare measured ionisation/flame signal to expected ranges to confirm a genuine ionisation fault.

2) Visually inspect the ignition electrode(s) and ignition lead: check for carbon/soot, cracked ceramic insulators, incorrect electrode gap or position, and signs of burning or contamination. Clean or replace electrode if damaged or fouled.

3) Check ignition lead and connections for continuity and insulation damage. Replace any damaged leads.

4) Test ignition transformer/ignition generator output and the ignition spark characteristics. Replace if out of specification.

5) Check earth/grounding of the boiler and the flame-detection return path. Poor earthing or lost reference can prevent a valid ionisation reading.

6) Inspect the burner and combustion chamber for condensation, soot, or deposits that could short or attenuate the ionisation signal. Remove condensate and clean combustion area as required.

7) Check the ignition electrode’s connection to the control PCB and measure flame-detection circuit components (resistors, sense connections) for correct operation. Repair wiring harness faults.

8) Test the PCB’s flame detection electronics; if the PCB is defective in the flame-sensing circuit the PCB may need replacing.

9) Confirm gas valve operation and gas pressure at the burner if weak combustion is suspected. Low gas pressure or a partially blocked air intake/flue can create a weak or unstable flame that gives a poor ionisation signal.

10) After repairs or replacements, run multiple ignition cycles and verify stable flame detection and normal operation. Clear stored diagnostic codes and observe for recurrence.

Important notes and next steps

1) Do not attempt to remove burner covers, electrodes, gas valve or PCB if you are not Gas Safe registered. These are live, gas-carrying and potentially dangerous components.

2) If the fault persists after basic checks or if you are unsure: book a visit from a Gas Safe registered engineer. Provide them with the fault code (D.44), a description of what you tried, and any other codes or observations.

3) If you smell gas at any time, treat it as an emergency and follow the gas-safety steps above.

Summary: carry out only the safe, non-intrusive checks listed above. D.44 indicates a flame/ionisation sensing problem and usually requires a qualified Gas Safe engineer to properly diagnose and repair ignition/electrode/wiring/PCB or combustion issues.