Programmer and timer

1 Types of control

Vaillant's glossary describes a plug-in timer or programmer as mechanical or digital, allowing either one 24-hour pattern or each day to be set separately¹. It also describes programmable room thermostats, which combine timing with temperature and can set a separate time for a hot water cylinder². Baxi's list of boiler controls includes room thermostats, room programmers, and digital or mechanical timers⁵.

Where the timer sits varies. On Vaillant's 2023 ecoTEC plus boilers, a built-in timer is only activated and visible when a particular control is connected⁶. Viessmann's Vitodens 050-W manual says that in room temperature-dependent operation, time programmes can only be adjusted at the room controller⁷. Ideal's Logic+ guide simply refers to the programmer's own instructions⁸. Use the booklet for your control, as menus are not universal.

2 Checks if the heating does not come on

User manuals treat this as a first check before calling anyone.

1. Check the programmer is set to on or is in an on period (Worcester Bosch Greenstar 4000)³
2. Check the times are as you want them and that the room thermostat is turned up (Ideal Logic+)⁹
3. Make sure the timer is set for central heating on, and see any instructions supplied with it (Baxi Platinum)¹⁰

If those are right, the next places to look are the room thermostat and the boiler display. See reading a fault code.

3 Heating schedules

Advice on how to use a schedule is not uniform. Baxi suggests a schedule so that heating is used only when it is really needed, and Ideal says to review it when your routine changes¹¹¹². Vaillant and Ideal both prefer heating when the home feels cold to leaving it on all day¹²¹³. These are makers' opinions, and no official comparison was reached. Vaillant separately warns against leaving a system unused in winter while you are away¹³.

For leaving a house empty in cold weather, Worcester Bosch's Greenstar 4000 manual says to leave an external programmer on constant, with the thermostat at 12 °C³. See frost protection for how other manuals differ.

4 What England's rules say

Approved Document L covers time controls in England. Hot water from a store should have time control separate from the heating circuits⁴. Where hot water and heating already share one time controller, they may continue to do so after the work is complete; otherwise each should have separate time controls⁴. Replacement boilers bring further requirements, listed under boiler building regulations. Rules in Wales, Scotland and Northern Ireland are not stated here.