Central Heating Boiler or System

coldguy

Central Heating sometimes works sometimes doesn't, currently it won’t fire up.
When it does work the radiators don’t get up to normal temperature.

I spoke to the boiler manufacturers, Vaillant, and had a guy out who told me it was a system problem and probably a blockage and the wiring to the boiler had not been installed properly. The boiler has however worked fine for 8 years up until this autumn.

I had the system power flushed but this hasn’t sorted the problem.

Not sure what to do next, any help appreciated.

WIAWSNB

Blimey, talk about a blank sheet of possibilities!

Oookkkaaaay, the boiler is 8 years old? That ain't old. How old is the rest of the system - the rads and pipes?

Does the boiler have a pressure gauge? Do you have a hot water cylinder? 

And... does the boiler have a magnetic filter fitted to the return pipe before it enters the boiler? If so, when was it last checked? Do you know how to do this? The content of that filter should be very informative.