The Avanta Plus is designed to have a purpose made time switch installed within the boiler casing. The installation instructions though show how an external timer and thermostat can be fitted instead so I am not sure why your electrician sees a problem with the Drayton.
Maybe there are other issues that are not obvious from your description but I am not quite sure what they could be.
All he said was that the Drayton was a single channel and the Boiler needed a two channel timer. According to the suppliers of the boiler it only needs a single channel as you only need to control the heating side, the hot water is on demand anyway.
The boiler is fitted in the loft. The friend who supplied the boiler had a word with plumbers who fit these things in his area and they said the Drayton was the right one.
The boiler is working perfectly as fitted but as is in loft needs to be controlable from inside bungalow, to boost heat or overide timed heating.
Think you have really answered your own question. Yes, a two channel timer can be fitted, but there is no need to as you say because the water is on 24hr demand anyway. Who wants to turn on a hot tap and find out the hot water is off????
The single channel timer will do exactly what you need.
I still can not wire the flipping thing up no matter what I do.
I used 1m/m 3 core cable and used the earth as the return feed (after putting brown insulation sleeve on). The timer unit lit up but the boiler did not respond to the unit. And the thermostat did not do anything.
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