|
|
 |
|
|
|
|
|
|
This is the hints and tips page for central heating Programmers and Timeswitches.
This page describes the various types of timeswitches and programmers available, and general hints on how to change a failed one. Also documented, is how to research, and carry out a conversion from an “old style” backplate to a standard 6 terminal back-plate, that will take any standard programmer or timer.
Types of control:
There are two broad types, mechanical time-switches, and fully electronic programmers. The first type usually consists of a 250v (clock) motor driven timing disk, with movable segments, for controlling the on/off times of the hot water and radiator circuits. There are usually a couple of rocker switches for constant or timed hot-water, and central-heating. The fully electronic ones (that can properly be described as “programmers”), with control relays, and a circuit board to control them and the LCD display are more versatile, and have many more on/off times available. Once the times are set via the simple push-button sequences (similar to setting your LCD watch), they stay set unless changed. The timings will stay in the electronics even if there is a mains failure, since there is a backup battery.
General fault guide and replacement hints:
The mechanical time-clock driven programmers can deteriorate over some years, especially if they are located in the hot environment of the airing-cupboard. The typical symptom is that the clock dial will stick, so the program on/off timing will then be wrong. The hot water and heating will still be controllable via the timed/off/constant switches.
The electronic ones rarely go wrong, but the LCD display, or the circuit board electronics, or a relay can fail. If you already have a standard universal backplate behind a failed electronic one, then usually a replacement just plugs straight in its place. You may find one or two small retaining screws holding the unit on to the backplate, usually top and/or bottom edge, then it just pulls off the backplate.
A replacement will probably cost between £30 and £40.
|
|
|
 |
|
|
QE2 programmer available from THERMSAVER.
|
|
|
|
|
|
|
|
The following picture shows the INTERNAL representation of what the typical electronic programmer does in terms of its contacts, and also shows how the contacts are used.Note that the TIMER (usually an electronic one, but could be a mechanical time clock), will already be connected internally to the LIVE and NEUTRAL. The wiring in the OLD backplate will need to be reviewed so as to be compatible with that of the 6 contacts as shown. This is for controlling a typical 3 position valve controlled heating and hot water system, and the schematic will be similar to the contacts in a QE2 from THERMSAVER or the C27 from HORSTMANN. Note that THERMSAVER have an excellent page on programmer backplate replacement wiring, so that you can put in a standard backplate, or replace an older mechanical one with a new QE2. Please see the link to that page HERE: http://www.thermsaver.co.uk/heating_controls/update_or_replace.html
If you already have a universal standard backplate fitted, then the new programmer should be a plug compatible fit. However, most suppliers recommend that the new backplate that comes with the new programmer is fitted, as the backplate contacts will be in a known good condition. Please check with the table at the linked page above in case any wiring changes are needed when replacing your old model
Note that the QE2 programmer has some nice extra features, like a winter/summer switch, and day groups selection as well as individual day on/off times, with up to 28 individual selections per channel (i.e. 28 for hot water on/off times, and 28 for central heating). Logo and links by kind permission of THERMSAVER.CO.UK
|
|
|
|
|
|
Typically contact 1 (often a yellow wire) will go to the satisfied side of the cylinder thermostat, contact 3 (blue) will go to the common connection of it, and contact 4 (may be red) goes to the COMMON connection of the room thermostat.Contact 6 will not necessarily be needed,as it is an “off” position anyway. Always check with the programmer supplier before changing any wiring. Most of them have helpful technical departments, who will usually reply to a technical question if you supply your suggested connection diagram for confirmation.
|
|
|
|
|
|
|
Thermsaver Heating Solutions offer efficient, effective solutions on the supply and installation of a complete heating package, including gas boilers, oil boilers, stainless steel unvented cylinders, room thermostats, programmers and other heating controls, heat recovery ventilation and central vacuum systems.
|
|
|
|
|
©2004,2005 www.letsfixit.co.uk
|
|
