water pressure surge

I get that sometimes if the water heater has heated a batch of water, which expands slightly as it heats and so pressurizes the system a little bit more than normal.

Water swells when heated..therefore pressure can increase in system.
Air pocket at top of WH Tank is used to control pressure increases....air can be compressed/water can't

And some systems just need an 'accumulator' installed to control pressure increases form heating water

This includes cold water also?

dtappy3353 wrote:
This includes cold water also?

Depending on where any check valves are in the water heater, yes it can include cold water as well. In the simplest setup, with a three valve (or some two valve) water heater bypass or no water heater bypass, there are no check valves at all for the water heater, so the static pressure on the cold and hot lines is exactly the same. If there's a check valve at the inlet to the water heater, the pressure increase is restricted to the hot side.

(There is still some measurable increase in pressure when heating water even with an air pocket, though it's moderated considerably over having no air pocket, since the pressure of the air goes up slightly with the small decrease in volume of the air and a bit more with its increased temperature.)

dtappy3353 wrote:
At times during the day, when we turn on a faucet (hot or cold) even flushing the toilet, we get a surge of pressure in the line.

Could this be my pressure control device is failing or has failed?

Thoughts?

Read the above information, maybe just a simple matter of re-establishing the air pocket in the water heater. But yes, your water pressure regulator may be leaking and not controlling the pressure over time.

I agree you fill the tank with COLD water and heat it it gets hotter the system pressure goes up. Due to the check vlave at the inlet.

And if you use a pressure regulator device the heater also actrs like an "Accumulator" (Pressure tank) so if the device is one of those cylinder shaped things that can't pass more than about half a gallon per minute and maintain pressure you will get an initial surge being 45 PSI but the regulator can't keep up. Not a problem with mine as mine can pass several gallons per minute.

The other definition of water pressure "Surge" is what is called water hammer this happens when you turn it off (The pipes rattle). But You said when you turn it on so I won;t bother with it.

If the regulator is working, that's all it has to do. Something like a Camco hi flow regulator (which passes many gallons per minute) is NOT going to CAUSE this issue if it isn't broken.