First of all, there are two versions of the Hive receiver, and the wiring is different depending upon which version you have.
There are also several variants of TRAC timer. Yours appears to me to be a single channel timeswitch. From memory, and based on the info in your post I seem to think it is likely that:
Terminals 1 & 2 are voltage free switching contacts
Terminal 3 is the Live of the 230V supply
Terminal 4 is the Neutral of the 230V supply
Can you confirm this? The information should be in the instructions for the timer, and also usually printed on, or inside the timer somewhere.
If this is the case, things don't quite add up. If your boiler was a combi, and didn't have any stored hot water (aka a hot water cylinder) a single channel timeswitch is fine. However, if you do have stored hot water and central heating, a single channel timeswitch controlling both heating and hot water so that they are both either on or off together would be unusual, and not suitable for direct conversion to Hive without some rewiring and possible plumbing modifications.
Also, as I said before, there are two versions of the Hive.
1) The single channel version of the Hive is for combi boilers without stored hot water. If you use this to replace a single channel timeswitch that is presently controlling the heating and hot water together, the hot water won't work when the Hive room thermostat has turned the heating off, and during the summer when the house is warm.
2) The dual channel version of the Hive is for controlling central heating and hot water. If you tried to replace a single channel timeswitch with this, some significant rewiring and possibly the addition of a 3-Port motorised valve would be required.
To be more definitive, the following information is required:
Confirmation of the functions of the terminals 1 to 4 at the existing timer.
Details of what is connected to the other end of each of the 5 wires.
Details of the type of plumbing / heating system that is being controlled. (ie fully pumped, gravity hot water with pumped heating, Y-Plan, S-Plan, combi etc.,)
