Hi I'm James
I wouldn't waste your time or mine servicing your un-vented
Heating system for £30.00 I wouldn't insult you.
With un-vented systems you must have good mains pressure. and economy 7 or 10 then hopefully plentyfull of hot water.
When I see people slagging off...
A tip for you Tony, I have replaced a couple of these units recently, they where the 600 models, they must be flushed properly, check the rads for cold spots, if you find any, needs flushing again.
James