Economical Central Heating

I don’t know if there’s a general answer to this, or whether it depends on your specific circumstances.

I’ve just moved into a newly built flat with a combi boiler and radiators. Is it cheaper / greener to have the heating on a timer (coming on twice a day for 2-3 hours with the thermostat set at about 22 degrees), or to juggle the thermostat (ie mostly having it on a low temperature, say 15-18 degrees, and turning it up into the 20s if we’re cold - this would vary between 0 and 4 hours a day in winter?

Or is there another method that makes more sense?

I wouldn’t shut off the heat entirely or the place can freeze. Burst pipes being the obvious type of damage you can have.

Setting the thermostat to the lowest setting will save fuel if you only plan on heating the home warmer for a few hours.

Use a programmable thermostat.
You can set it to have the temperature warm when you get up in the morning, much colder when you are away at work, warm when you get home, and then cool at night when you are in bed.

This can save quite a bit of energy.

I don’t think I can change the thermostat as it’s a rented flat, but this sounds like what I’m doing anyway, except I do it manually. The obvious downside is that it’s a bit cold first thing and when I get home from work, but I can live with that (it doesn’t take too long to warm up).

Putting a programmable thermostat in is a very simple procedure (we did it at our last house). You could theoretically put one in, and replace it with the original one when you move out (or leave it if your landlord would like it to stay). Or you could talk to your landlord now and say you’re willing to take on the cost of putting in a programmable one; they might not mind.

ETA: Forgot to say that programmable thermostats are the cat’s pajamas - we live in Calgary where it’s been around -30ºC for the last couple of weeks, and we love ours.