Control Of Your System; General Description Of Controls In Your System; The Way To Use A Programmer - Honeywell Home ST9420C User Manual

CONTROL OF YOUR SYSTEM

General Description of Controls in Your System

Your Honeywell Home ST9420C provides timing control for both your central
heating and hot water systems, letting you set ON and OFF periods to suit your own
lifestyle.
The ST9420C does not directly control the temperature but works together with
other temperature controls, such as room thermostats and cylinder thermostats or
sensors, to control your heating and hot water system in your home.
With 7-day programming and up to 3 on/off periods per day, every day can be set
differently, and heating and hot water can be set at different times from each other.
ST9420C also has a Boiler Service reminder / Shut-down feature, which helps
ensure your gas boiler is regularly serviced in compliance with UK Gas Safety
Regulations. For more details see pages 18 & 19.
Your system may include a DT92E wireless room thermostat, and/or a CS92A wireless
cylinder sensor. These products use state of the art 2 way RF communications to share
information and give you robust and flexible control of your indoor environment.
The following instructions explain how to programme and use the ST9420C, and
associated controls, to provide the most home comfort at the least cost.

The way to use a Programmer

Think about the time periods when you are typically in the house and when you are
not, and also the times when you use a lot of hot water. These are the times you
should use as the basis for the programmes. It will be necessary to allow some
heat up time for the heating system after periods when it has been off – this would
typically be 1 - 1½ hours, depending on your house and your preferences.
If Optimum Start has been selected (see page 17), you do not have to allow for this
heat up time as the Programmer is intelligent and will calculate the correct starting
time for your house. This is based on measurements it makes about your system
characteristics, and on the current and target room temperatures. All you have to do
is programme the time periods when you want to be comfortable.
Other features are commonly available on the Programmer to enhance comfort and
convenience, for example, OVERRIDE, EXTRA HOUR, and MODE buttons.
A typical use of the OVERRIDE feature is when you return home unexpectedly for the
rest of the day and the heating is off. Just press the heating OVERRIDE button and
the heating will come on until the next programme time, at which point it will follow
the normal programme. The advantage here is that you do not have to remember to
switch off because the normal time programme does this for you.
A typical use of the EXTRA HOUR button would be if you returned to the house for
a short period when the heating and hot water were off. Pressing the appropriate
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