I was only pointing out that there are other options.
The QAA 73 is expensive as is the open therm controller quoted by Trianco -about £700 on Parts Center price list. I don't care how good the controller is, in my opinion, is not worth that amount of money. It is also a point to note that it could be a new boiler fitted into an old system and why would you go to the expense of fitting an open therm controller to a 25 year old system.
You would really have to weigh up the options, is it a basic domestic system or do you have other so controls, DHW controls etc ? You can fit a programmable timer, plus a room stat and you probably have individual TRVs fitted as well ? I have seen so many systems that have an open therm unit fitted in say the lounge, great - lounge comes up to temperature and shuts heating down - rest of house is still cool so programmer turned up and lounge TRVs turned down. I've even seen the programmers tuned up to maximum and the TRVs used to control the house temperature so why spend all that money when it's not being used to its full advantage. The same in offices, the programmer fitted in one office (typically the smallest and nearest radiators) so when this reaches temperature every other office freezes. Maybe it's me being cynical but I'm just no convinced they are as good as everyone thinks. Great from a sales point of view but not for the engineer that has to then try and explain to the customer that the unit detects the temperature where it is fitted and controls to that point irrespective of the rest of the building.
You can get programmable room stats, you can also get wireless ones. It really comes down to your budget and how much you are prepared to spend. This plus the efficiency of your actual system - is it new or is it just a boiler upgrade ? There are many controls on the market nowadays including programmable individual thermostatic radiator valves. All down to budget at end of the day.
I personally have a Strata 1/38 Combi boiler with an RE 2132 room unit, a remote room sensor in hall (allowing both all and lounge to dictate the flow temperature and an outside sensor for direct on boiler weather compensation, I also have a cylinder (for a power shower) with cylinder stat fitted and wired to override the outside sensor and give DHW priority on the cylinder, then switch back to compensated heating circuit. My gas bills have dropped considerably over past two years due to the controls as well as fitting cavity wall insulation.