Hi. Really sorry that I neglected your thread, NB - I'd forgotten about it :-(
If you are set on the Halo, first check that your specific Ideal model will take it. If it does, then by all means fit the WiFi receiver in the boiler, and mount the 'Halo' anywhere you want.
Do bear in mind you'll still have a cable running to your existing wall 'stat position, which presumably will be power-isolated when you remove the old boiler timer, but you'd need to confirm. The simplest solution at the wall 'stat end is to remove the 'stat, safely terminate the cables, and place a decor faceplate over it.
Where will you have your Halo - wall-mounted, or sitting in a stand? It looks nice, but is costly for a non-Smart unit, so I hope it's easy to program and use, because that's where Smart wins every time - just a doddle to monitor and change temps from your phone.
'Smart' undoubtedly saves energy too. If we find we are snug enough with a blanket over our knees whilst watching Justice - Those Who Kill, I'll often grab the phone and turn the CH down or off. If we are going out, ditto. Then another press when we know we are heading home.
Let us know what you decide, and how you get on.
