We will only fit boilers with a stainless steel heat exchanger, usually the boiler is an Alpha
the main reason for this is that we have been installing these for years.
We are also the local Alpha Service Agent, so that means we carry spares and knowledge to repair it, should the unforeseeable happen.
Sometimes we will use a Viessman or Vailant, but that is dependant upon your unique situation.
Some boilers are manufactured with aluminium heat exchangers and are cheaper, but in our experience, we have seen that the corrosion from the aluminium and the condense has blocked the condense waste, caused problems with flueing of combustion products and have damaged the heat exchanger beyond repair.
With Stainless Steel this should not happen.