Vaillant main heat exchangers

[Hason]

Hi people hope all well,maintaining a number of boilers and got a vaillant heat hex kettling as I have sorted system out but just wondered if I can clean main the main hex? Due to the micro bore style water ways I'm unsure if it will bypass or if can soak with liquid or use fernox ds40.
Any thoughts or advise would be fantastic
Cheers for your time

 

[Phill Peck]

Doesn't always work but have had some success flushing them

Chemical of your choice in the boiler isos off put it on p2 and run a tap. (Combi)

If it's a system again do with isos shut through bypass but you'll have to cycle between p2 and p0

Heat only only way really is to come text power flusher straight onto flow and return but heat is a bit of an issue

 

[Hason]

Thanks I was going to fit machine straight on flow and return I've got an immersion heater as doing any flush cold is a waste of time.
Thanks for feedback