No heating check battery programmer

If you have a battery-operated programmer/room thermostat that’s showing a low battery symbol you will need to change the batteries.

There are various types of programmers, and the advice on how to change them varies. 

The most common types are Baxi and Danfos TP1. You will need two good quality AA batteries (e.g., Duracell, cheaper batteries will not work).

If it's a baxi remote programmer you will have to put a flat headed screwdriver in the slot underneath and twist, the front should pop off.

You will find a little groove/slot on the underside of the programmer. To remove it from the wall, insert a small flat headed screwdriver into the slot. Twist the screwdriver and the programmer should pop off, revealing the batteries. Refit the programmer into its holder on the wall once the new batteries have been fitted.

If it's a Danfos TP1 insert a flat headed screwdriver or something similar into the slot underneath, in the middle, and push upwards being careful not to drop it. The Programmer should pop out of its holder (be careful not to drop it).

Remember to put the programmer back in its holder on the wall once the new batteries have been installed.

Mains powered programmers will not have a battery low power display, but if you are not sure if it's mains powered, or battery operated do not attempt to remove it. 
Is the heating now working?