Car doesn, t energise heater relay when ignition starts

There are a few possibilities.
However, more than likely this is the main relay or the fuel pump relay.
Fuel injected vehicles prime the pump when the key is put into the run position. This is so fuel pressure is ready when the key is turned to start the engine turning over. It sounds like the relay started to fail since it was clicking twice. Your owner manual might have the position of this relay. It is generally right under the dash near the steering column.
Electrical items are tough to diagnose because they can fail gradually or abruptly. It sounds like the hard starting is due to lack of fuel pressure which should be provided by the pump relay before starting it.

Nest time you go to start it check a few things;

Turn the key to run, does the rely still click at all? If so is it still twice?
If it clicks, try to listen where it is coming from to locate the relay.
Before starting the engine, but after turning the key to the run position, pull a spark plug.
Does the plug look wet from fuel? You may have to pull more than one.
Another possibility can be the momentum cut-off switch. This is part of the emergency fuel cut off which turns off the pump in a wreck. They can also fail gradually.
Has your vehicle been in a wreck recently?

Let me know how it goes and I will keep an eye on this post to help fix your problem

There are 2 likely places to look for high amp relays;
First, under the dash near steering column
Second, (Thsi is most likely where it is), there is a Fuse/Relay box under the hood of the vedicle. If you remove the cover and flip it over it should have a schematic of the Fuses and relays in the box.
I am asking around to see if anyone that works oversees is familiar with your vehicle and I will send you a message if I find out the location for sure.
I am glas things worked out and youare very welcome and please come back with any issues or car advice needed soon.

Take Care

Dr. C