Thanks all. The customer has asked me to fit an thermostat / time programmer that they can set with ease. I'm not sure which one they have at the moment.
I've never wired a programmer to a combi boiler. Is there any additional wiring needed for this or is it the normal permanent live, beatral and switch live?
You don't wire a programmer to a combi.
Let me explain: A programmer is used when you have a system boiler with a hot water storage tank. The programmer tells the boiler when to heat hot water only, the radiators only or both together.
A combi boiler does not have a hot water storage tank - it heats the water for the sink / bath etc. on demand. When you turn a hot water tap on, the boiler fires & heats the water to that tap and stops heating the water when the tap is turned off.
If at the time you turn the tap on the boiler is heating the radiators, the boiler will stop heating the radiators for as long as you have the hot water tap turned on and will return to heating the radiators as soon as you turn the hot tap off.
This is all done by means of the differential valve and the diverter valve which are built into the combi boiler.
Therefore you do not need a programmer - only a timeswitch to tell the boiler when to start heating the radiators in the morning before you get out of bed and again before you come in from your days work. You also need a room thermostat to tell the boiler to turn off when the house is at the desired temperature.
One of the easiest thermostats to wire to a combi is the
Drayton RTS8, and a simple timer is the Danfoss 103 Mechanical Timeswitch as I mentioned in post #3
Personally, I prefer a Programmable room stat which is a timer and thermostat combined in the same enclosure. It is easy to install, very versatile allowing for different temperatures to be set for different times of the day, but can be too complicated for some folk to set / use. One such Programmable Room stat is the Honeywell CM900 Wireless as mentioned in post #2. This uses a wireless receiver which is wired into the terminals inside the boiler & receives instructions transmitted by radio from the thermostat which can be placed almost anywhere in the house.
The boiler manufacturers installation instructions will show where to wire a timer & thermostat to and these instructions should have been left by the installation engineer with the householder - it's a requirement to do so - but if they can't be found you can often download a copy in PDF format from the boiler manufacturers website.