Just an update.
Got the money back form SEI with 4 weeks.
The heating is massively improved.
1. Water is being heated by gas, this should be much cheaper.
2. We turned down the temperature of the water, now its just hot enough to wash your hands, no more scalding immersion water.
3. The rads are hotter because only half of them ore on at a time (because of the zones).
4. Its so easy to put the heating or water on for a bit more with the boost button, no more reprogramming the heating for one night and ending up baked the next night. We have the heating set to come on at a lowish level and can boost it to be warmer with one touch.
5. House is warm, not alternating baking and freezing.
6. Digital thermostats are very accurate, no more bobbing on and off for the boiler as the thermostat goes on and off.
7. Saving a fortune by only heating downstairs at this stage of the year. Upstairs just does not start getting cold until December.
Very happy customer. I'd recommend anyone to get this done.