I believe so. With heat, you have evaporation. I pour in enough washing soda to dec my voltage to around 12volts and when water evaporates, the volts can increase drastically if you don't watch it. If you're like many fellows here and have the cathode as close to the surface as possible, your water will evaporate to the point that your cathode wont be touching the solution anymore. Likewise, I use larger solution (4L vs 250ml-500ml) so your results may vary. I keep a close eye on my solution but it might not be necessary for you.