Vaillant Ecotec 824 R1 - random noise when heating ON

[TomAlex35]

Hi

I'm dealing with Vaillant Ecotec 824 R1 in one flat. The boiler make a very loud noise when central heating is on - this is random and occurs mostly at night.

I'm sharing video showing the problem:

So far we changed:

1. Expansion vessel
2. Pump
3. Water pressure gauge - analogue sensor

Additionally we added Magna Clean filter.

But the issue still occurs randomly only when central heating is on (never happened when boiler heats up water). 99% of cases it happens at night only. When we turn on central heating during the day all is well. We have theory that at night it runs for long and that's when the issue is triggered. Also, when it does happen and we switch the boiler off, and then back on the issue doesn't occur in our tests.

Does anyone know what might be causing this noise?

Thanks.