I haven't changed the timer recently, and it's a very simple gravity fed boiler. I hadn't considered the pump, which is very old, but hasn't given me any problems. He while installation was here already when I bought the house 5 years ago. How would I be able to check the pump is the culprit?
I couldn't pin down precisely how many times it trips, but it went from intermittent to constant within 2 days. I have isolated the central heating timer and the rcd is now fine. I can't
Get to the wiring on the pump as it's underneath the cylinder! I've called a heating engineer.