How do I remove Valiant analogue 130 timer from Turbo max combi boiler ?

The time clock is faulty and I need to remove it from boiler. I believe these are just plug in push on, but it is very tight to remove at the non clock end. I have released the catch on the right hand side which allows slight movement, but left hand side of timer is very tight. Do I just pull it or is there a simpler answer.