Can I replace my boilers internal analogue timer with an external digital one?

Often you can. I have done this numerous times on equipment where the existing timer was obsolete / not available or a more conveniently positioned one was required. You will probably need the connection / wiring diagram for the old timer so you can connect the new one correctly. A good heating engineer or electrician should be able to supply a suitable timer and sort this for you.

Hope this helps

In most cases the answer is no. Call the company that made the timer and talk to a tech. They can answer your question and give instructions on how to do it if you can. Good luck!

No you can't. It has a probe inserted into the block to read temputure and also pressure.

without that, you loose the safty feature of the guage.