Timer Wiring Diagram

Timer Wiring Diagram

230V COMBI BOILEER

LOW VOLTAGE / DRY CONTACT COMBI BOILER

S & Y BOILER PLANS EXPLAINED 

S and Y Plans are still used to form the basics of most domestic heating systems, however, there is often confusion between both plans and how they work. 

Central heating system designs can differ from house to house, based on the requirements of the property. 

However, the majority of properties in the UK use either an S Plan or a Y Plan heating system. S and Y plans have been designed to give you close control of your central heating system, ensuring that your heated water is diverted to the correct areas. 

S and Y plans are also a way to ensure that your boiler interlock works. 

This is when your boiler automatically switches itself off when there is no demand for central heating of hot water in your home. 

The style of system chosen for each household can be influenced by many factors including the size of the property, the provision of an unvented cylinder and space, such as a compact airing cupboard, which may not have room for the system bypass required for S plan designs, and so may lend itself to a Y Plan.

 S PLAN 

An S Plan Heating System has two separate motorised valves, one that controls the heating, and the other controls the hot water. These valves can be used individually to control the heating system. It is also possible with an S Plan that further zones can be added by adding additional thermostats and motorised valves to each circuit. 

Whenever either the central heating or hot water port is needed, 230V is sent down the Motor Live wire (usually the brown wire) 

The motor inside then turns the valve, opening the body of the valve, allowing the heating pump to push water through. 

Once the valve is pushed all the way open, it also pushes down a microswitch, activating the circuit between the Permanent Life (usually a grey wire) and the Switch Live (usually orange in colour). Once the 230V hits the Switch Live, the boiler ignites. 

Once the demand for either hot water or central heating is fulfilled (either the timer is turned off, or the thermostat reaches the desired temperature) the power to the Motor Live (Brown) wire is lost, so the valve body springs back and shuts off the flow through the valve. 

At the same time, the microswitch making a circuit between the Permanent Live (Grey) wire and the Switch Live (Orange wire) is opened, resulting in no power being sent through and the boiler will stop running.

 Y PLAN BOILER AY 

Plan has a single, three-port valve supplying both the central heating and/or hot water. 

This three-port valve is shaped like the letter 'Y' when you look at it from a schematic layout of pipework point of view, as seen below. 

This is where the name 'Y' comes from.

 DISTRICT HEATING WITH ELECTRICAL CONTROL VALVE