I've recently had an extension built with a new Glow Worm 30ci combi
boiler fitted.

There is a little old pipework remaining and one small rad otherwise
the system is new.

My previous gravity system gave no trouble, apart from the occasional
pump, it worked faultlessly but owing to a need for instant hot water
I went for a combi.

After 16 months the secondary heat exchanger failed, as I had not had
the apparently mandatory service this was not covered by warranty so I
had a very expensive repair.

The service engineer said this was due to the system not being flushed
as the heat exchanger was blocked.

I am now led to believe that system flushing appears to be a necessary
requirement for combis due to the design, how important is this
flushing, I would have thought any modern boiler should have some
filtering system to prevent fouling of the internals.

Geoff Lane