Paul Barker
Minefield.
Basically mate the cheaper the boiler the less money the manufacturer has to spend on r and d and parts quality. Secondly the less profit he makes.
So what is the result, very little r and d, cheapest parts on the market (his cost not yours, see later) and to make up for his lack of profit in selling you the kit originally he will claw back a profit from sale of spares.
We call a cheap boiler a sprat to catch a Mackeral.
Cheapest option is to buy the most expensive boiler you can afford.