removed same boiler last week in st helens and replaced with vaillant 831 and wireless stat for 1600 quid.system water was clean so only needed cleansing, draining and then cold flush.
i work from st helens and can give you a quote if you wish.You dont have to remove new hot water heater if you would rather not.Theres a few options you can consider.Get quotes now in preparation , so you have time to consider options.