Immersion Heater causing SNR drop?

[nellisere]

Our immersion heater to heat up the water turns on between 17:15 and 18:15, at those times, my noise margin drops from 3dB to nearly 0dB causing an unstable connection. Our router is plugged into the master socket at the front of the house on the ground floor, the immersion heater is upstairs at the back of the house, would you think it is the immersion heater causing this drop, if so is there any filters I can put in place to stop this?

[146Kg]

I'd try putting the immersion heater on at vastly different times of the day and not 17:15-18:15 to prove it is the cause.
Unless there is telephone extension wiring in the vicinity of the hot water cylinder (and even then) it seems unlikely to be the culprit.

[nellisere]

It's started going down at 16:40, at 2.6dB now. I'm not really sure what else it could be. We have storage heaters but they're all electric and come on between 1am-6am, our immersion heater is the only thing that is turned on at the times when the noise margin goes down? I'll try putting the immersion heater on later tonight for an hour and see what happens.

[146Kg]

It may not be self inflicted, interference from a neighbours appliance could be to blame. I'd still go with your plan of putting it on at a different time to prove/disprove it is the heater, not just an extra hour as if the water is already hot it wouldn't be doing anything in the extra hour.