Are all 433mhz transmitters equal?

I've got a central heating boiler relay unit which takes a 433mhz signal from a wireless room thermostat.

I got to thinking about this and I figured it might be nice to be able to build something using an arduino to talk to it.

So, I was thinking, what does a '433mhz transmitter actually mean - are there tons of different protocols / chips that work on 433mhz, none of which can talk to each other, or are the protocols used so simple that most 433mhz chips can talk to each other?

ie. is there some simple way of getting a not too expensive receiver / transmitter pair to connect to an arduino which might allow me to first reverse engineer the protocol used by my boiler relay and then transmit using that protocol, or do I need to know what chipset it is using before I have a chance?

I can't get into the box to see the wireless chip, but I've got a picture of the internals of the board if that might help (on here) annoyingly not quite close up enough to see the receiver chip name. http://www.tfc-group.co.uk/assets/graphics/static/ET4_Pairing.pdf

I can't see the transmitter chip inside the sender either.

cheers,

Joe

Aha, receiver is himark rx3310a. Which is an amplitude shift keying receiver, whatever that means.

Does that help at all? Any chance that a cheap 433 mhz transmitter / receiver pair off ebay will be able to talk to this system, or will I need the exact same chips?