I contacted both Viessmann and Valliant boiler manufacturers for their local recommended installers. The Vaillant installer supplied a quote quite quickly, Charles Bickham was a little slower.
I chose Charles as he was competitive compared to the Valliant guy and was the installer of my preferred boiler Viessmann.
One of his guys Jack arrived on the agreed date and time and started work straight away after I gave him a walk through of our house. He wore a mask at all times, was very polite, tidy and hard worker. His standard of work was high, he was very knowledgeable and efficient.
I had new system boiler fitted ( my old boiler was vented) along with a new motorised valve, tank thermostat (at my request) and he removed pump and heating header tank in loft, as well as a power flush.
I would highly recommend Charles Bickham especially if it's Jack who carries out the work. Invoiced as per original quote.:)