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PLEASE RESPECT YOUR ENVIRONMENT!
Take care to dispose of this product and any
packaging or literature in an appropriate way
WHAT IS A PROGRAMMER?
...an Explanation for Householders (as recommended by the Energy Savings Trust)
Programmers allow you to set 'On' and 'Off' time periods. Some models switch the central heating and
domestic hot water on and off at the same time, while others allow the domestic hot water and heating to
come on and go off at different times. Set the 'On' and 'Off' time periods to suit your own lifestyle. On some
programmers you must also set whether you want the heating and hot water to run continuously, run under
the chosen 'On' and 'Off' heating periods, or be permanently off. The time on the programmer must be
correct. Some types have to be adjusted in spring and autumn at the changes between Greenwich Mean
Time and British Summer Time. You may be able to temporarily adjust the
heating programme, for example, 'Override', 'Advance', or 'Boost'. These
are explained in the manufacturer's instructions. The heating will not work
if the room thermostat has switched the heating off. And, if you have a hot-
water cylinder, the water heating will not work if the cylinder thermostat
detects that the hot water has reached the correct temperature.
WHAT IS A ROOM THERMOSTAT?
...an explanation for Householders (as recommended by the Energy Savings Trust)
A room thermostat simply switches the heating system on and off as necessary. It works by sensing
the air temperature, switching on the heating when the air temperature falls below the thermostat
setting, and switching it off once this set temperature has been reached. Turning a room thermostat to
a higher setting will not make the room heat up any faster. How quickly the room heats up depends on
the design of the heating system, for example, the size of boiler and radiators. Neither does the setting
affect how quickly the room cools down. Turning a room thermostat to a lower setting will result in the
room being controlled at a lower temperature, and saves energy. The heating system will not work if
a time switch or programmer has switched it off. The way to set and use your room thermostat is to
find the lowest temperature setting that you are comfortable with, and then leave it alone to do its job.
The best way to do this is to set the room thermostat to a low temperature – say 18ºC – and then turn
it up by one degree each day until you are comfortable with the temperature. You won't have to adjust
the thermostat further. Any adjustment above this setting will waste energy and cost you more money.
If your heating system is a boiler with radiators, there will usually be only one room thermostat to
control the whole house. But you can have different temperatures in individual rooms by installing
thermostatic radiator valves (TRVs) on individual radiators. If you don't have TRVs, you should choose
a temperature that is reasonable for the whole house. If you do have TRVs, you can choose a slightly
higher setting to make sure that even the coldest room is comfortable, then prevent any overheating
in other rooms by adjusting the TRVs.
Room thermostats need a free flow of air to sense the temperature, so they must not be covered by
curtains or blocked by furniture. Nearby electric fires, televisions, wall or table lamps may prevent the
thermostat from working properly.
Honeywell Control Systems Ltd.
Arlington Business Park,
Bracknell
Berkshire
RG12 1EB
50047645-008 A
Technical Help Desk: 08457 678999
www.honeywelluk.com
© 2011 Honeywell International Inc.
User Guide
2
Y9420S Sundial RF
Pack 3
How to use:
ST9420C Wireless Enabled Programmer
DT92E Wireless Room Thermostat
CS92A Wireless Cylinder Thermostat
BDR91T Wireless Enabled Relay Box (if installed)
This document is to be left with the user
and forms part of a Home Information Pack
System Components
This section is to be completed by the Installer
Location
ST9420C
DT92E
(typically in living room or hallway)
CS92A
(typically next to hot water tank, in bedroom)
BDR91T
(If installed, typically next to boiler)
Energy Efficiency and the Environment
Home energy use is responsible for more than ¼ of the total UK carbon emissions
which contribute to climate change. Heating and hot water systems based on
boilers account for
of this figure, so it is important to understand how your
controls can help to maximize energy efficiency while maintaining your comfort.
Your Programmer should be used in conjunction with appropriate temperature
controls. In order to save energy the following general points should be observed:
1. Ensure your system contains a room thermostat and a hot water thermostat,
and that both are set to appropriate temperature levels: typically 20°C for the
room temperature and between 50 - 60°C for the hot water temperature.
2. Programme your heating and hot water to be off when you are not in the house. If
you are concerned about possible frost damage to any exposed pipe work, it is
advisable to fit a frost protection system – your installer can advise you about this.
3. Think about how you use your domestic hot water – if you have a storage
system, it is not necessary to have this switched on all the time, even when you
are in the house.
4. Consider the heat up times required for your central heating. Every home
responds differently when the heating is switched on. Adjust the start time so
that you are not cold when you get up in the morning. A shorter heat up time is
required for other heating periods.
5. In the evening, when the house is up to temperature, it is often possible to
switch off the heating up to an hour before you go to bed, without any noticeable
reduction in comfort.

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Summarization of Contents

Control of Your System
General Description of Controls in Your System
Explains the ST9420C programmer, DT92E thermostat, and BDR91T relay box for central heating and hot water control.
The Way to Use a Programmer
Guides on setting time periods for heating and hot water based on lifestyle and comfort preferences.
The Way to Use a Room Thermostat
Guides on setting room thermostat for comfort and energy saving, and interaction with heating systems.
Control of Your Boiler
Explains how the boiler is controlled by the ST9420C timer or BDR91T relay box.
Optimisation
Details features like Optimum Start, Delayed Start, and Optimum Stop for energy saving.
Getting Started with Your ST9420C
Step 1: Setting the Date & Time
Provides instructions for setting the date and time on the ST9420C programmer.
Step 2: Running a Built-in Programme
Explains how to use the default built-in programmes after setting date and time.
Programming Your ST9420C
The Built-in Programmes
Presents pre-set heating and hot water schedules (Profiles A, b, C) as starting points for programming.
Reviewing the Programme Times
Guides on how to check programmed ON/OFF times for hot water and heating.
Modifying the Hot Water Programme
Details the steps to adjust hot water ON/OFF times for each day.
Copying One Day's Programme to Another Day
Explains how to copy a day's programme to other days for convenience.
Programming a Different Day
Guides on setting programmes for individual days separately.
Modifying the Heating Programme
Details the steps to adjust heating ON/OFF times for each day.
Disabling or Enabling Time Periods
Explains how to disable or re-enable specific ON/OFF time periods.
Operating Your ST9420C
Choosing the Operating Mode
Describes how to select heating/hot water modes like OFF, AUTO, ONCE, CONT.
Overriding the Operation Without Changing the Programmes
Explains how to temporarily override heating or hot water ON or OFF.
The Extra Hour Function
Details how to add extra hours to heating or hot water periods.
The Holiday Function
Guides on setting a period to switch off heating/hot water while away.
Enquiry Mode
Explains how to view system information like room and water temperatures.
Fine Tuning Your ST9420C
Changing from AM/PM Time Display to the 24 Hour Clock
Instructions on switching between 12-hour and 24-hour clock formats.
Changing the Installer Parameters
Introduces how to adjust installer settings for system preferences.
Optimum Start Parameters
Explains installer parameters for Optimum Start, Delayed Start, and Optimum Stop.
Optimisation
Illustrates how Optimum Start, Optimum Stop, and Delayed Start features work.
How to Set Your Hot Water Set Temperature
Guides on setting the desired hot water temperature via Installer Mode.
Boiler Service Reminder
Countdown to Service
Explains the countdown display for upcoming boiler service.
When Service is Due
Describes actions when boiler service is overdue.
Operating Your DT92E
Inquiring about the Set Temperature
How to check the set temperature on the DT92E thermostat.
Adjusting the Set Temperature
Steps to change the set temperature on the DT92E thermostat.
Switching Off
How to put the DT92E thermostat into standby mode.
Frost Protection
Describes the frost symbol and its meaning for the heating system.
DT92E Operating Indicators
Low Battery Indicator / Battery Replacement
How to identify and replace low batteries in the DT92E.
RF Communications Indicator
Explains the RF symbol indicating communication status.
Lockout
Describes the lockout symbol and its implications for overriding controls.
DT92E Energy Saving ECO Feature
Entering ECO Mode and Setting the Energy Saving Time Period
Guides on activating ECO mode and setting its duration.
What Happens in ECO Mode?
Explains the display and functionality during ECO mode.
How to Exit ECO Mode
Instructions to deactivate ECO mode and return to normal settings.
Fine Tuning Your DT92E
Changing the DT92E Installer Parameters
Introduces adjusting DT92E settings via Installer Mode.
To Enter Installer Mode
Steps to access the DT92E Installer Mode.
To Change a Parameter
Steps to modify a parameter value in DT92E Installer Mode.
Operating Your CS92A Hot Water Thermostat
Basic Operation
Explains the function and components of the CS92A.
Battery Replacement
Instructions for replacing batteries in the CS92A.
Error Indications
How to interpret error lights on the CS92A transceiver.
Operating Your BDR91T Relay Box (If Installed)
BDR91T Controls Layout
Identifies controls and indicators on the BDR91T relay box.
Automatic Operation
Explains how the BDR91T controls the boiler based on wireless signals.
Temporary Manual Override
How to temporarily override the BDR91T's current state.
Loss of Wireless Communications
What happens and how to respond to communication loss with BDR91T.
FAQ and Troubleshooting
Setting the Time on ST9420C
Step-by-step guide to setting only the time on the ST9420C.
Automatic Clock Changes
Information on automatic clock changes and potential configuration.
Recovering from Programming Errors
Advice for recovering from programming errors on the ST9420C.
Behaviour During Power Failure
Explains behaviour during power loss and recovery.
Troubleshooting RF Communication Loss
Steps to resolve loss of RF communication between devices.
Changing CS92A Batteries
Signs and procedure for changing CS92A batteries.
Changing DT92E Batteries
Signs and procedure for changing DT92E batteries.
Thermostat Override Capabilities
Explains thermostat override capabilities based on programmer mode.
Troubleshooting Guide
A guide to diagnose and resolve common system problems.
DT92E Low Battery Indication
Addresses DT92E low battery indication.
Blank DT92E Display Troubleshooting
Troubleshooting steps for a blank DT92E display.
CS92A Low Battery Indication
Addresses CS92A low battery indication.
Troubleshooting 'NO SIGNAL' for DT92E
Troubleshooting 'NO SIGNAL' for DT92E communication.
Troubleshooting 'NO SIGNAL' for CS92A
Troubleshooting 'NO SIGNAL' for CS92A communication.
Troubleshooting 'NO SIGNAL' for BDR91T
Troubleshooting 'NO SIGNAL' for BDR91T communication.
Troubleshooting 'SENSOR FAULT' for DT92E
Troubleshooting 'SENSOR FAULT' for DT92E.
Troubleshooting 'SENSOR FAULT' for CS92A
Troubleshooting 'SENSOR FAULT' for CS92A.
Configuration & Service Data
Configuration Data (to be completed by Installer)
Tables for installer to record system configuration settings for ST9420C and DT92E.

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