Y-Plan and S-Plan



The following animations show each mode of operation by highlighting the path from the programmer to the boiler.
Hot water only
Central Heating only

Hot water and central heating
Both calling
HW satisfied, CH calling
HW calling, CH satisfied
Both satisfied  

Hot water calling
Central heating calling 

Flame Rectification
Basic AC and an explanation of flame rectification 
Earthing  (Word document)

The Honeywell web site has a vast amount of information and includes details of all the Sundial plans.
Have a look at

Please note that all information on this web site is provided 'as is' . Whilst every effort has been made to ensure its accuracy, no responsibility can be accepted for any damage, loss or other misadventure as a result of its use.

Page created and maintained by John Turnbull