Error D.36

Safety first

- If you choose to do any checks, isolate electrical power at the boiler fused spur before removing the front cover. Do not work on gas valves, the burner or PCB connections. If you smell gas, leave the property and call the gas emergency number immediately.

Initial quick checks for a homeowner

1. Note the exact error (D.36) and behaviour (no hot water, boiler locks out, any other fault codes).

2. Try a normal reset of the boiler (use the boiler reset procedure in the manual). If the fault clears but returns, continue to the checks below.

3. Check system water pressure on the gauge. If pressure is very low (<1.0 bar) top up using the filling loop (if you are comfortable doing so) and re-test. Low pressure can cause unrelated fault behaviour; top-up may clear some faults.

4. Check hot-water taps and isolation valves are open and that you have a mains cold-water supply to the boiler.

Safe basic inspection (only if comfortable and after isolating power)

1. Isolate the boiler electrical supply at the fused spur. Confirm power is off.

2. Remove the front cover to gain visual access (consult manual for safe removal). Do not touch exposed circuitry with the power on.

3. Locate the domestic hot-water flow/temperature sensor connector and wiring — typically on the hydraulic module near the plate heat exchanger or DHW outlet pipe. Look for an obvious loose plug, corrosion, water ingress, damp wiring, or a cracked/soiled connector cap.

4. If you find a visibly loose plug, gently disconnect and examine the pins for corrosion or moisture. Dry with a clean cloth and allow to air dry. Re-seat the plug firmly.

5. Inspect any removable filter caps or screens near the flow sensor area for blockages or water in the cap. If a cap is visibly dirty or wet, clean and dry it before reassembly.

6. Refit the cover, restore power, call for hot water and observe whether D.36 returns.

If the fault persists or you find wiring damage

- Do not attempt to repair or replace sensors, wiring, or internal components yourself. D.36 often requires measurement of sensor resistance, continuity checks, and possibly replacement of the NTC/flow sensor or wiring harness, which are tasks for a qualified Gas Safe engineer.

What to tell the engineer when you call

- Provide the exact error code (D.36), whether the fault clears on reset and returns, what steps you have already taken (power reset, pressure topped up, any visible loose connector found), and describe any damp or corrosion you saw. This helps the engineer bring the right parts and diagnostic equipment.

When to call a professional

- Call a Gas Safe registered engineer if the D.36 error persists after the basic checks, if you find damaged wiring, if you are not comfortable isolating power and inspecting the connector, or if the problem recurs. A professional will safely test the sensor (NTC resistance at temperature), inspect/replace the wiring harness or flow sensor, check the hydraulic components and the PCB, and restore safe operation.

Important final note

- Avoid repeatedly attempting resets as a long-term fix. Any internal sensor or wiring fault needs proper diagnosis and repair by a qualified engineer to ensure safe, reliable boiler operation.