Hope someone can help please. I am thinking of moving the expansion tank for an immersion heater into the attic however this will require the vent pipe to go under the level of the tank before it rises up into the tank in the attic. The tank is high above the immersion heater but the track of the vent pipe would need to go downwards first. Is this possible/advisable? Are there any regulations controlling this? Any help would be appreciated. Thank you.