The price of parts vary from boiler to boiler, so it is hard to give prices until our team confirm the cost of the exact part required. Don’t be afraid of demanding the very best service you can get, after all. Why not spread the cost of your new boiler? monthly installments starting from as little as £12 a month. The price of a vaillant boiler will be determined by the type and size of boiler required but can range from £740 to £1,500, not including installation, which can bump up.