Potterton Prima 60F- can you start it manually?

You don't say what timer you're using or what's wrong with it. It might be possible to switch the boiler manually or even jury rig some kind of override switch IF YOU KNOW AND UNDERSTAND WHAT YOU ARE DOING but honestly just replace the timer. Assuming it's a separate wall mounting timer/programmer it'll probably just be slacken 2 screws underneath, lift the timer away, pop on a new one, tighten 2 screws and follow the manual to set it up.

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October 2022