This page is still being written, and has not had any form of review or comment.
Do not rely on any information presented here.
--John Rumm 03:56, 18 November 2007 (GMT)
This article discusses some of the many and varied ways in which thermostats are wired into domestic central heating systems.
<cautionary statements about mains voltages etc>
What does a thermostat actually do?
A thermostat is a simply a temperature controlled switch. In its simplest form the switch will default to closed or "On" until the stat reaches a preset temperature. Once it is warm enough, it opens or turns "off".
The temperature at which this happens is usually selected by a user adjustable control.
Do I need one
Yes. If you dont have one, the boiler will keep cycling when the programmer switches it on, even through a hot summer, thus wasting fuel and adding wear and tear to the boiler.
TRVs alone don't maintain a fully stable temperature, so again heat will be wasted when temps rise above what's required for comfort.
Cover heating system interlock, TRVs etc.
How many should I have
Discuss cylinder stats, multiple zones, UFH etc.
Types of thermostat
diagrams and piccies of trad Honywell style stat
Cover why there are a number of variations and explain things like:
- Anticipator / Compensator heaters
- Changeover contacts
- Frost protection
- Aux switching and contacts
- Optimising stats
What does the thermostat control
- Connecting to a boiler
- Controlling a zone valve
How should I wire it
- Type of cable
- Earthing or lack of
- what to do with spare neutrals
What else can I control with a thermostat
- other apps including switching electric heating loads directly
- cooling loads
- over temperature alarms and sensors.