Error D.33

Safety precautions:

1. Do not attempt to carry out any work on gas valves, pilot assemblies or internal combustion parts. Only a Gas Safe registered engineer should work on gas components.

2. Before doing any visual inspection or basic checks, switch the boiler off at the boiler on/off button, then isolate electrical power at the mains or the fused spur feeding the boiler. Confirm the display is off and there is no power.

3. If you are in any doubt about isolating the boiler safely, stop and call a qualified engineer.

Initial checks a homeowner can do (safe, non-intrusive):

1. Record the exact error code and any other messages on the display so you can tell the engineer (e.g. D.33 and any F codes).

2. Try a simple reset: turn the boiler off, wait 10–20 seconds, then turn it back on, or press and hold the boiler power/reset button for 5 seconds as per the manual. Note whether the code clears and whether the boiler attempts to run. If the fault clears and does not return, monitor for recurrence.

3. Check air intake and flue terminals externally (on the roof or wall): look for obvious blockages such as bird nests, leaves, snow, or debris. Clear any safe, external obstructions you can reach without climbing or forcing access.

4. Make sure vents and air bricks in the property are not blocked and that the boiler has adequate ventilation.

5. Listen to the boiler during a start attempt: if you hear the fan trying to run (whirring) or a repeated clicking, make a note — this information helps an engineer.

Specific diagnostic and fix steps (only proceed if you are competent and have isolated power; do not touch gas parts):

1. After isolating power, remove the front service flap (if comfortable) to visually inspect the fan area for obvious debris (dust, birds' nest, paper). Only remove loose debris with care; do not force or disassemble components. Re-fit the cover before re-energising.

2. With power still off, gently try to rotate the fan impeller by hand (if accessible) to check for free movement. It should turn smoothly without unusual resistance or scraping noises. If it is stiff, seized or rubbing, do not force it further — this indicates a probable mechanical failure and you must call an engineer.

3. Visually inspect accessible wiring and connectors to the fan for loose or damaged connections. If you see a clearly disconnected plug that you can safely re-seat (and you are confident doing so), isolate power first, then reconnect and secure it. Re-apply power and test. If unsure, stop and call an engineer.

4. If you are able to re-run the boiler after these checks and the error persists, note whether the code appears immediately during startup or only after a short run — this helps diagnose sensor vs. motor failures.

5. Do not attempt to replace the fan motor, PCB, or internal sensors yourself unless you are a qualified heating engineer. These parts require specialist testing equipment and certified persons to replace and re-commission safely.

When to call a professional and what to tell them:

1. Call a Gas Safe (or local qualified) engineer if the fault returns after a reset, if the fan will not spin freely, if you found damaged wiring or connectors, or if you did not feel safe performing the basic checks.

2. When you call, tell the engineer the exact boiler model (Vaillant EcoTEC Plus Regular), the error code D.33, what you observed (noise, whether the fan tried to run, any visible debris or damaged connectors), and whether a reset temporarily cleared the code.

3. A competent engineer will have the tools to measure fan speed (tachometer), check fan motor operation, test the fan speed feedback sensor, inspect and test the PCB outputs, verify flue pressure/flow, and replace faulty components if needed.

Final note: Because a fan fault affects combustion safety, do not repeatedly force the boiler to run if the D.33 code persists. Use your heating/hot water backup if available and arrange for a professional to inspect and repair the boiler.