Installed a new regulator, but pressure peaks overnight

[motocrossmann]

All-

I just replaced the inlet water regulator on my house with a new unit. The pressure had been as high as 90psi and now I'm generally down to about 45psi throughout the day. The only oddity is that overnight I can see that it spikes at about 80psi for some reason. What gives?

George

 

[johnjh2o]

Do you have a thermal expansion tank on your water heater?
https://www.plumbingsupply.com/hotwater.html#expans

 

[motocrossmann]

Nope! Old home so it never had one. Time to install an expansion tank! Thanks!!!