Customer called us today because they were having some alternating water pressures when running fixtures. They told it happened throughout the day but only after not running water for a while. We went ahead and tested the water pressure and my gauge read 55 psi. It did not change from this point indicating rising water pressure due to a failed prv. We then tested the thermal expansion tank and found it had failed. We replaced the thermal expansion tank and secured it to the structure with an approved mounting bracket. We set the pressure inside the tank to 60 psi. Restored water to the home and ran air from the lines. We had customer run fixtures as well to ensure the problem is resolved. They were happy with our work and our response time today. No issues when we left.