Sounds like it is trying to draw a lot of current from an insufficient circuit, or even a spur circuit.
Mine did this on the last brew whilst I was working on a machine.
My circuit for the garage is only a spur and it could not handle it.
The RCD's on modern fuse boxes are pretty sensitive and it only takes 1 additional electrical item to be turned on to trip them. Even the fridge tripping in can upset them.
Up grade the particular RCD the the boiler runs on. The house will still be safe because you can only buy approved upgrade RCD's
Not entirely correct, always great to offer experience and help but best not offer electrical advice if you're not sure what you're talking about... :thumb: