DOMESTIC HEATING CONTROLS ARE EASY
PART 2 - TIMERS & PROGRAMMERS
Today’s inescapable need to improve energy efficiency in UK homes has brought installers many opportunities to
make extra earnings through the upgrading of heating and DHW controls. Often, however, misunderstandings and
technical ‘mystique’ surrounding some of these products inhibits installers from fitting the most appropriate energy
saving devices that can cut household heating bills, improve comfort levels and reduce carbon dioxide emissions
into the atmosphere.
This series aims to remove some of the doubts and show that domestic heating controls really are easy.
TIME CONTROLS
Running a domestic central heating/hot water system continuously is prohibitively expensive for most users. One
certain way of holding down a home’s heating bills is to switch the system off as often as possible. Of course, this
can be done only when room and domestic water heating are not needed.
Time controls on most domestic heating/hot water systems are among the first essentials for improving home
comfort and reducing running costs. They trigger the controls ‘chain of command’, sending automatically timed
On and Off instructions to other system components. Each user-set, timed switching programme helps maintain
desired comfort levels and prevents excessive fuel consumption by inhibiting unnecessary boiler firing.
Winter temperatures in the UK are rarely low enough to keep the heating on overnight, so we usually cut heating
costs and sleep better in a cooler room by using a time control to automatically switch off the system late evening
and on again early morning. Also, we use the same timer to set Off and On periods during the daytime for
additional benefit.
Fig.1 shows a simplified typical heating controls wiring sequence. The time control governs when the heating
system operates whilst the thermostats and valve auxiliary switch provide the electrical interlock that prevents the
boiler firing if there is no demand for heat.
TIME
CONTROL
THERMOSTATS
(ROOM OR
CYLINDER)
RELEVANT
MOTORISED
VALVES
BOILER
AND
PUMP
Motor opens valve(s),
activates auxiliary switch
to boiler/pump
Sends timed ON/OFF
signals to thermostat
If heat demand exists,
switches close and
pass signal to valve(s)
Boiler can fire only
when a demand for heat
exists
Fig.1
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