Good day and thanks in advance for the wisdom.

I live in a new home (3 years). During construction, I had them pre plumb for a sprinker system and put in the backflow preventer outside. The "T" for the sprinker system stems from the cold water feed almost at the same location it splits for the cold feed on the hot water heater.

I have noticed alot that many times (yes, I watch late at night in the basement) that my hot water heater cycles A LOT more on nites when the sprinklers run than on days it does not. I also notice the cold feed going into the hot water heater get really hot too when the sprinklers are running.

I have had the home builder plumbers check to make sure nothing was cross plumbed, but cold to cold and hot to hot checked out.

So my quesion, is there any potential that the sprinklers could be pulling so hard on the cold water feed to actually back suck hot water out of the hot water heater (thru its cold feed). And if so, what is best remedy, will relocating the sprinkler feed to cold water FURTHER from the hot water heater help (as the junction for both sprinker and hot water heater cold feed are at the same location)?

THanks in advance, and i would LOVE to save on my gas bills (in the summer).