Is the sunvic sp2 a 2channel timer please

Yes. It appears the Sunvix SP2 is 2-channel timer.
http://www.sunvic.co.uk/documentation/Programmer_Select_207.pdf

Two-channel means CH central heat and WH water heater can be programmed separately, and each can have its own timing program.
pg 3

The timer offers pre-programmed options for both CH and WH, which can be used, or program your own schedule. chart pg 5 and steps pg 3

Limitations: both channels operate on same clock time, and dip switch setting. pg 6. So the WH cannot be programmed for 5-2 weekdays-weekends and CH programmed for 24 hour.
As a convenience for varied work schedules, Sometimes people use the 5-2 weekday-weekend option so 2 days of week can have different programming, and then fudge current day setting during the set-current-time step pg2 so the 'weekend days' are actually moved to wedsday-thursday instead of sat-sun.

Option: both CH and WH timer programs can be linked and follow same programming by using copy button. pg 5

Using advance button on either side of timer, pg 3-4, WH and CH timing schedules can be overridden temporarily until next set point is reached. Then regular programming automatically resumes.
If override or Advance button is pushed for either CH or WH, it reverses whatever programming is in effect. On becomes off, or off becomes on. However if CH thermostat is satisfied and room temperature has not fallen below thermostat set point, then override will not turn CH on, but override will turn CH off. Same for WH override: If cylinder thermostat is satisfied with internal water temperature, the water heater will not turn on and heat more water, but the override can turn water cylinder off.

Unit requires Cr2033 lithium button battery. Pg 6. Probably lasts 3-5 years. Programming is protected for 30 days from power outage.
If programming is lost, change battery, the reset timer and reprogram to restore functionality.

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