'Flash' from Switch in Hot Press

Hi,
As part of the rewiring of the 30-year-old house, the immersion heater (of which the 'sink' element wasn't working), switch and the timer had been replaced.
The new timer is the type with 24-hour, 15-min 'slots', with 3 settings - OFF, TIMER and ON, and fitted on the wall immediately above the switch. It is noticed that when we flick the switch to turn on the immersion heater, a 'flash' appears behind the toggle (hard to name that part on the switch, if you get my meaning). We informed the foreman of the building contractor who engaged electricians to do the re-wiring about 'flashes', and he said that's OK - push the toggle more quickly. But the 'flash' still appears whenever the switch is set on.
Is that safe or not? Did any of you, AAMers, ever come across this?

We have not yet paid off the builders, and will hold onto the final instalment, until that is sorted out. How can we convince the foreman (or indeed the boss of the building contractor) about the 'flash' issue?
Many thanks,
Allendog

most switches produce a spark. You're just probably seeing it better as I assume the switch is in a nice dark hot press. Hence you should never smiwth on/off a socket, light switch etc. if you suspect a gass leak!

While I agree with Legend to some degree, I don't think it's as simple as all that. I would ask them to have a look at it. Also, make sure you get a sfety repot signed off before they leave. Maybe you should ask the foreman to switch the swtch on and off - if he thinks there is somehting wrong he won't be too happy to do it if there's a chance it will shock him. Cruel way I know but it's your safety at the end of the day!