Car takes a long time to heat up?

I have a ford fiesta 1.3 2003 it take a very long time to heat up. Once it does it's fine but wondering why it takes so long. Also my fan is constantly on. Comes in even when engine is stone cold. Even when I disconnect the fan it takes a long time to warm up. I checked the thermostat today and that is ok. Also. I have noticed that it loses quite a bit of coolant over a few days. So having to constantly top it up. But I can't see any obvious leaks…
I'm drawn towards a heater matrix problem. Any other ideas before I part with money…

Thanks
Andrew

Added (1). Also my car does not have A/C or a windscreen demister.

It is a 16 year old Fiesta. What do you expect?

If the fan is always running it would take longer for your coolant to heat up, which opens a thermostat, which gives you heat. I wouldn't worry about it.

You say the thermostat is OK, but it obviously isn't! Replace thermostat with a new one.

You took the thermostat out and boiled it in water to see if it opened? Anyone with a brain would have just replaced the thermostat.
If you don't have any leaks you have a bad head gasket and are burning coolant. Have a mechanic do a "block test" to verify a bad head gasket.
You are over heating the motor and don't realize it. When there's air in the cooling system the radiator fan will run and the temperature gauge will not be accurate.